V. DISCUSSION

It is well understood from the literature that the physical and chemical

characteristics of water in any locality exerts their influence on the occurrence and

abundance of the biological components. Although physico-chemical properties

have an effect on the biological processes, many of them are subtle and intricate,

hence cannot be clearly understood. Among the various categories of water body,

it is in the brackish water environment such as estuary, where the magnitude of

influence of physico-chemical parameters on the biological resources is

comparatively higher which makes the environment more dynamic. A proper

understanding of any biological problem in the estuary is possible only if the

physical and chemical characteristics of the environment are properly

documented.

5.1. Meteorology 5.1.1. Rainfall

During the investigation, the study area experienced 3296.10 mm total

annual rainfall (Table 1). In the pre-monsoon season, May and April month

experienced moderate rainfall of 4.68%. During the monsoon season (June and

September months), study area received high rainfall of 89.52%. Whereas in the

post-monsoon season, (October and November) experienced a moderate rainfall of

5.99%. No rainfall was observed during the month of January, February and

March.

5.1.2. Air temperature The air temperature recorded during the period from January to December

2005 fluctuated from 25.64°C to 34.22°C (Table 2). The seasonal variation in the

air temperature revealed that the region exhibited three distinct temperature

regimes. The higher regime during pre-monsoon season and the lower regime

during south west monsoon season and third moderate regime in post-monsoon

season. Therefore from the data observed, it is revealed that air temperature

exhibited a trimodal seasonal oscillation. Similar seasonal fluctuation was

documented by Sahu (1981), Reddy (1982), Patil (1987), Puranik (1990), Ronald

(2001), Vijay Kumar (2002) and Chandrashekara (2004) while working on the

various brackish water environments along the coast of Dakshina Kannada and

Udupi district. In the present study, a trimodal seasonal oscillation could be due to

the observations made even during monsoon season. From the data, it is believed

that the intensity and the duration of south west monsoon winds by and large

control the air temperature in this region. However, the small drop in the air

temperature during the north east monsoon is also common.

5.2. Hydrography

5.2.1. Water temperature

The water temperature during the present study fluctuated from 23.30oC to

33.2oC with an annual range of 9.90oC (Table 3). Ansari et al. (1986) recorded an

annual range of 8.40oC in Mandovi-Zuari estuary. In the same estuary,

Krishnakumari et al. (2002) observed 29.78oC as a mean surface water

temperature. However, the highest range of 13.0oC was observed by Prabha Devi

(1994) in Coleroon estuary. Menon et al. (1977) recorded a range of 7.0oC

between highest and lowest water temperature in Mangalore waters. Patil (1987)

observed a range of 6.8oC between highest and lowest in Nethravati-Gurupur

estuary. In the same estuary, Vijay Kumar (2002) and Tripathi (2002) documented

an annual range of 5.50oC. Chandrashekara (2004) observed an annual range of

5.40oC in Sita-Swarna estuary. While comparing the annual ranges recorded by

various authors, it became evident that the water temperature fluctuated between

the maximum and minimum was high in Haladi-Chakra estuary. This increased

range could be due to the higher quantity of freshwater drainage from rivers to the

estuary or the intrusion of up welled waters in the estuarine basins from the

adjoining coastal waters. The other climatiological parameters in this region might

also have contributed for the high annual range of water temperature between

lowest and highest in the present study.

The seasonal variation of water temperature in Haladi-Chakra estuary

revealed a gradual increase in trend from February and reached a maximum in

May. The onset of monsoon brought down the water temperature to a very low

level during September. Gradual increase in water temperature during post-

monsoon season was observed at all the stations with a small drop in the month of

December. Thus from Figure 2, it is evident that the water temperature exhibited a

clear cut bimodal seasonal oscillation with two highs and two lows. Similar

seasonal variation observed by Bhat (1979), Patil (1987), Puranik (1990), Vijay

Kumar (2002) and Chandrashekara (2004) in various brackish water environment

of west coast of India.

5.2.2. Water pH

In the present investigation, the surface water pH exhibited a seasonal and

spatial variation. During pre-monsoon season, pH varied from 7.13 to 8.12 and in

monsoon season from 6.61 to 7.61. While during post-monsoon season, the

surface water pH fluctuated from 7.51 to 7.99. From the Table 4 and Figure 3, it is

clear that pH was high in May at all the stations. Similar high pH values were

observed by Puranik (1990), Ronald (2001) and Tripathi (2002) in Nethravati-

Gurupur estuary. The lower values of pH at all stations coincided with south west

monsoon season and the presence of freshwater throughout the estuarine basin due

to monsoon season. Kaliyamurthy (1976) observed minimum pH values during

south west monsoon season and opined that reduction in values were due to

presence of freshwater in the estuaries.

Several workers have been reported the lower values of pH during south

west monsoon season in the Nethravati-Gurupur estuary. Bhat (1979), Reddy

(1982) recorded a lowest pH of 6.4 during August. While Nagrajaiah (1981)

observed a low pH value of 7.01 during July. The lower values recorded in the

month of July during the present study is in agreement with the works carried by

various authors in the estuaries of Dakshina Kannada. A gradual increase in trend

during the post-monsoon season was observed in the present study. This increase

in trend could be due to the presence of seawater in the estuary. Similar

explanation was put forwarded by Patil (1987) and Puranik (1990). The spatial

distribution of surface water pH revealed generally higher values at stations

located in confluence region. While stations located away from the confluence

registered lower pH throughout the period of study. From the data gathered, the

pH values of surface water were not only found to be dependent on the season, but

also to the proximity to the sea.

5.2.3. Water dissolved oxygen

The composition of water along with temperature significantly influence

dissolution of atmospheric gases and its holding capacity. The situation gets

further complicated in estuarine environment, which is subjected to diel and tidal

variations. In the present investigation the surface dissolved oxygen content in this

estuary ranged from 0.0 to 7.81 mg/l with an annual range between highest and

lowest to be 7.81 (Table 5). Menon et al. (1977) and Bhat (1979) recorded an

annual range of 4.8 ml/l and 3.9 ml/l respectively in Nethravati-Gurupur estuary.

Puranik (1990) and Vijay Kumar (2002) have reported an annual range of 2.2 ml/l

and 5.97 ml/l respectively in the same estuary. Reddy (1982) observed a

difference of 2.69 ml/l between two extreme values in Mulki estuary. However,

Chandraskekara (2004) have registered an annual range of 3.70 mg/l in the Sita-

Swarna estuary, Udupi.

In the present study, the lowest dissolved oxygen of 0.0 mg/l was recorded

at two stations. While in other three stations was between 0.41 to 2.05 mg/l. This

low dissolved oxygen values have affected the annual range at a great extent. This

lower value of dissolved oxygen is perhaps being due to intrusion of up welled

waters. In the present study, dissolved oxygen of 0.0 to 0.41 mg/l was recorded at

station 1 located at the confluence and at station 3 and 5 located nearer to the

confluence. Whereas, stations located away from the confluence registered

comparatively higher values of dissolved oxygen. Manoj kumar (1988) observed

low oxygenated water in the Malpe estuary and opined that the low oxygenated

condition could be due to intrusion of up welled water. Reddy et al. (2005)

recorded dissolved oxygen content as low as 2.19 mg/l in the coastal waters of

Mangalore. The authors have related this low dissolved oxygen due to the

occurrence of Tsunami in Bay of Bengal in December 2004.

Except the low dissolved oxygen in the month of September the surface

water dissolved oxygen exhibited normal spatial and seasonal variation. During

the pre-monsoon season, the dissolved oxygen content was found to reduce

gradually reaching the lowest in the month of May. This is found to be quite

contradictory to the observations made by De’souza (1977), Patil (1987), Puranik

(1990) and Vijay Kumar (2002). This change in the present study could be

directly related to the disturbances found in the Arabian Sea due to Tsunami

effect.

With the onset of monsoon there was a sudden rise in the dissolved oxygen

content reaching its peak in June and July. There after the dissolved oxygen

content decreased at all stations. Varma et al. (1975) have observed the maximum

dissolved oxygen content during the south west monsoon season in Mandovi

estuary. Qasim and Gupta (1981) observed a large changes in dissolved oxygen

content during south west monsoon season in Mandovi-Zuari estuary and opined

that oxygen cycle is closely related to seasonal changes. Bhat (1979) and Reddy

(1982) recorded higher values of dissolved oxygen during the monsoon season in

Nethravati-Gurupur estuary. However, Patil (1987) and Puranik (1990)

documented moderate values of dissolved oxygen during monsoon season in the

same environment.

The gradual increase in the dissolved oxygen content was observed from

October to January, forming a secondary peak. The seasonal fluctuation of

dissolved oxygen from the data revealed it exibit by and large bimodal seasonal

oscillation with two maxima in June and December and two minima in May and

September (Figure: 4).While Puranik (1990) and Vijay Kumar (2002) observed

secondary maxima during post-monsoon season and opined that this could be due

to increased incursion of distinct water mass flowing along the coast and

biological status of the environment with intense photosynthetic activity.

Chandrashekara (2004) observed one pre-monsoon peak and a major monsoon

peak followed by two small peaks in post-monsoon season in Sita-Swarna estuary,

Udupi.

The spatial variation of dissolved oxygen indicated that the stations located

at and nearer to the confluence registered larger variations between the months.

Whereas, stations located away from the confluence registered a narrow range of

variations between the months. Patil (1987), Puranik (1990) and Tripathi (2002)

observed a similar type of spatial variation in Cochin backwaters and in

Nethravati-Gurupur estuary respectively. Chandrashekar (2004) observed that the

stations located away from the bar mouth had registered relatively higher

dissolved oxygen than the stations located nearer to the bar mouth.

5.2.4. Water salinity

The perusal of the literature indicated that among various hydrographical

parameters, salinity variation in the estuary exerts a distinct influence on the

occurrence and distribution of organisms. Further, it is also known that salinity in

any estuary gets influenced by rainfall, evaporation, run off from the land drainage

and the degree of dilution of sea water by the freshwater. It is understood that the

influx of freshwater in an estuary will bring down the concentration of sodium

(Na) and chloride (Cl) ions, but bivalent ions like calcium, magnesium, potassium,

sulphate and carbonate ions increase in their concentration. Since these difference

in absolute concentration and their ratios will influence the movement of bivalent

cations between the organisms and environment affecting the osmotic property.

Therefore the selection and distribution of species in an estuary is influenced both

by total salt content and ionic concentrations.

In the present investigation, the salinity of surface water fluctuated from 0.21 to

34.49 ppt registering an annual range of 34.28 ppt between the two estuaries

(Table 6). Reddy (1982) and Patil (1987) registered an annual range of 35.90

ppt and 34.46 ppt respectively in Nethravati-Gurupur estuary. In Mandovi

estuary, Varma et al. (1975) recorded an annual range of 34.00 ppt. However,

lower annual range of 32.00 ppt was recorded by several authors in Hoogly-

Matlah estuary. Puranik (1990) recorded an annual range of 35.28 between the

two extreme values of salinity and Vijay Kumar (2002) recorded a range of

30.50 ppt in Nethravati-Gurupur estuary. From the data, (Table 6) it is evident

that both Haladi and Chakra estuary showed an Holohelinicum condition

(Kinne, 1971) during the study period.

Based on the seasonal variation of salinity, it is clear from the Figure 5,

that the estuary can be divided into three distinct salinity regimes, a higher saline

regime in pre-monsoon season, extremely lower salinity regime in monsoon

season and gradual increasing trend during post-monsoon season. The seasonal

distribution of salinity in various estuaries and brackish water was studied by

Menon et al. (1977), Bhat (1979), Reddy (1982), Patil (1987), Puranik (1990),

Tripathi (2002) and Chandrashekara (2004) along south west coast of India.

The higher saline conditions during the pre-monsoon season could be due

to low freshwater drainage and higher rate of evaporation. The extremely low

saline condition and pulsating regime during monsoon season between June and

August is obviously due to influence of freshwater during south west monsoon

season. It is interesting to note that there was sudden increase in salinity values

from less than 1.00 ppt in August to almost 22.0 to 24.0 ppt in September at

station 1, 3 and 5, which were located at and nearer to the confluence. Whereas

degrees of salinity increase is comparatively lesser at station 2 and 4 located away

from the confluence in Haladi-Chakra estuary respectively. This sudden increase

at the end of monsoon season indicates the intrusion of up welled high saline

water from the adjoining sea and coupled with reduced strength of riverine flow.

Similar observations were made by Chandrashekara (2004) in Sita-Swarna estuary

of Udupi district.

During the post-monsoon season, salinity values exhibited a pulsating

variation with peaks and troughs in every alternate months. However, it is

interesting to note that these conditions were within the brackish water conditions.

A critical look at the distribution of salinity at different stations during pre-

monsoon season indicated that the region underwent a clear mixoeuhaline

conditions (Venice classification). In June, July and August except at confluence

water the remaining stations exhibited a clear limnetic condition. However, the

study carried out by Puranik (1990), Tripathi (2002) and Chandrashekara (2004)

observed limnetic condition throughout the Nethravati-Gurupur and Sita-Swarna

estuary respectively. From September to January at all the stations exhibited a

clear mixoeuhaline condition, where salinity fluctuated between 5.0 ppt to 30.0

ppt. Thus, it can be stated that the whole estuary during the period of study

underwent three distinct types of brackish water conditions such as mixoeuhaline,

limnetic and mesohaline conditions. Such detailed classification of brackish

waters like Nethravati-Gurupur and Sita-Swarna estuary was documented by Patil

(1987), Puranik (1990) and Chandrashekara (2004) respectively.

5.3. Nutrients 5.3.1. Nitrogenous nutrients

5.3.1.1. Ammonia-nitrogen

Ammonia is one of the important nutrients often that regulates production

in aquatic environment. Generally ammonia is available in low concentrations in

natural waters and in turn gets regulated by certain important hydrographical

parameters such as pH, temperature etc. Being an intermediately compound in

nitrogen cycle its concentration is subjected to regular fluctuation during the

process of nitrification and denitrification. It is understood that ammonia is

preferred as a nitrogenous nutrient by many phytoplankton species.

In the present study, the ammonia concentration fluctuated from 0.10 µg-

at/l to 17.99 µg-at/l (Table 7) in the surface water. Nagarajaiah and Gupta (1983)

recorded from traces to 20.86 µg-at/l in the brackish water ponds of Nethravati

estuary. In the same environment, Suresh (1987) recorded values from traces to

29.17 µg-at/l. While Bhattacharjaya (1991) in Gurupur estuary recorded as high as

28.73 µg-at/l. Chandrashekara (2004) recorded the ammonia value which is

fluctuated between 0.95 and 16.51 µg-at/l in Sita-Swarna estuary.

In the present study, the ammonia value was found to be less when

compared with Nethravati-Gurupur estuary values, but was almost similar with

that of the values of Sita-Swarna estuary. This lower value could be due to lower

amount of domestic sewage discharge coupled with low quantity of offal in

Haladi-Chakra estuary. In Porto Novo waters along the east cost of India,

Ramadhas et al. (1976) recorded ammonia concentration which ranged from 0.76

to 1.5 µg-at/l in the brackish water. Raghothaman and Patil (1995) while working

in Narmada estuary, observed low levels of ammonia that ranged from 0.25 to

9.15 µg-at/l. During the present study, the seasonal fluctuation of this nutrient

gradually exhibited a trend and recorded the first peak in May at all the stations.

During monsoon season, a distinct peak was observed in July at all the stations

except at station 4 situated at Chakra estuary. There after a pulsating trend was

observed at all the stations in post-monsoon season, although the values were

lower but exhibited an almost increase in trend except in the month of December

where the concentration was very low at all the stations. From the Figure 6, it is

evident that the ammonia exhibited peaks in pre-monsoon and monsoon and

gradual stepping up trend in post-monsoon season. The pre-monsoon peak could

be attributed to intense biological activity, while the monsoon peak to the

increased freshwater drainage.

Nagarajaiah and Gupta (1983) observed monsoon and post-monsoon peaks

in the brackish water ponds of Nethravati estuary. Pradeep and Gupta (1988)

documented the peak values during June, November and April in brackish water

ponds of Mulki estuary. Tripathi (2002) documented pre and post-monsoon peaks

with varying intensity in the surface water of Nethravati-Gurupur estuary.

Whereas Chandrashekara (2004) observed trimodal seasonal oscillation in Sita

Swarna estuary. However, in the present study only two peaks were observed

which coincided with the pre-monsoon and post-monsoon season.

5.3.1.2. Nitrite- nitrogen

Among the three forms of nitrogenous nutrients, nitrite is considered to be

a very unstable form being an intermediately stage in nitrogen cycle. Nitrite gets

converted into a nitrate by nitrification or changes to ammonia or ammonium form

by denitrificaton process. In the natural waters, nitrite is generally available in

trace quantity.

In the present study, nitrite concentration varied from 0.20 to 4.23 µg-at/l

in the surface waters (Table 8). De’Souza (1977) while working on the monitoring

of some environmental parameters reported the values ranging from traces to

8.33µg-at/l at Zuari estuary. Sahu (1981) in Nethravati Gurupur estuary

documented the values varied from 0.02 to 2.01 µg-at/l. Nagarajaiah and Gupta

(1983), Suresh (1987), Pradeep and Gupta (1988), Sudhir (1990), Bhattacharjaya

(1991), Mathew (1994), Tripathi (2002) and Chandrashekara (2004) recorded

value ranged from 0.87 to 2.02, 0.35 to 8.72, traces to 23.15, 0.04 to 7.84, 0.04 to

5.85, traces to 3.5, 0.23 to 4.64 and 0.02 to 5.83 µg-at/l respectively, in the various

brackish water of Dakshina Kannada and Udupi districts. In Porto Novo waters of

east coast of India, Ramadhas et al. (1976) reported the nitrite values ranged from

0.64 to 2.61 µg-at/l in backwaters and estuarine regions. Santhanam et al. (1994)

recorded the range from 0.5 to 698.0 µg-at/l in Narmada estuary, east coast of

India. The present value is in agreement with the values recorded by Tripathi

(2002) in Nethravati-Gurupur estuary. In present study, the seasonal distribution

of this nutrient exhibited higher values in February at all the stations and there

after with a dip in the month of March. The values progressively increased and

reached a peak in July/September in almost all stations. In the post-monsoon

season with lower values in October and the nitrite concentration progressively

increased and reached to another peak in January. Therefore from the Figure 7, it

is evident that nitrite by and large exhibited trimodal seasonal oscillation.

Nagarajaiah (1980) recorded a primary peak in March in a semi-enclosed

brackish water pond of Nethravati estuary. Pradeep and Gupta (1988) recorded a

distinct primary peak during July in brackish water pond of Mulki estuary. Sudhir

(1990) documented a trimodal seasonal oscillation in the Nethravati-Gurupur

estuary. While Mathew (1994) documented a primary peak during January and

secondary peak in September in a semi-enclosed brackish water pond of

Nethravati estuary. Recently, Tripathi (2002) and Chandrashekara (2004)

observed trimodal oscillation of this nutrient in Nethravati-Gurupur and Sita-

Swarna estuary respectively. This spatial distribution of this nutrient revealed

lower values at stations located at and near to the confluence when compared to

those located away from it.

5.3.1.3. Nitrate-nitrogen

Nitrate is the end product of nitrification and is the most stable nitrogenous

nutrient. In recent years more attention has been given to nitrogenous nutrient

which is considered to be most potential limiting nutrient in the aquatic

environment in general and being particular in brackish water and estuarine water.

Goldman (1976) pointed out that in coastal phytoplankton species ratio of

nitrogen to phosphorus by atom is between 10:1 to 20:1. While in water it is only

5:1 therefore, enrichment of water with nitrogen enhanced algal growth which

proves that the nitrogen exerts its influence on primary productivity more than that

of other nutrients.

The present study showed nitrate concentration varied from 1.40 to 20.97

µg-at/l (Table 9). In Nethravati-Gurupur estuary, Sahu (1981) reported a values

ranging from 0.02 to 0.87 µg-at/l. Suresh (1987), Sudhir (1990), Vedamurthy

(1992), Mathew (1994), Gowda et al. (2001a), Tripathi (2002) and

Chandrashekara (2004) documented the values ranging from traces to 9.86, 0.10

to 6.85, 0.04 to 5.58, 0.02 to 3.08, traces to 7.28, 0.94 to 79.84 and 0.43 to 65.95

µg-at/l in Nethravati-Gurupur and Sita-Swarna estuary respectively.

Devassy (1983) and Devassy and Goes (1989) observed nitrate values,

which fluctuated from 0.23 to 0.92 µg-at/l. and traces to 3.76 µg-at/l in the

estuarine environments of Goa. In the same environment, Verlencar (1987) and

De’Souza (1999) recorded the values ranging from traces to 2.4 µ mol/l and traces

to 3.3 µ mol/l respectively. Krishna Kumari et al. (2002) in Mandovi estuary

recorded the values between 1.17 to 5.67 µ mol/l.

Along the east coast of India, Kannan and Krishnamurthy (1985) in the

Porto Novo aquatic biotope have recorded nitrate values ranging from 4.75 to

30.50 µg-at/l. Santhanam et al. (1994) in the Tuticorin Bay recorded values as

low as 0.2 to 0.7 µg-at/l. Gouda and Panigrahy (1995) in Rushikulya estuary

observed the nitrate values, which ranged from 0.37 to 18.4 µg-at/l. While

Ragothaman and Patil (1995) in Narmada estuary, documented the nitrate values

ranged from 0.5 to 775.00 mu. g/l.

The value recorded in Haladi-Chakra estuary is in agreement with the

values recorded by many authors worked along the west coast of India. It is

evident from the Figure 8, that the first peak was recoded in April/May at all the

stations. The second peak values were observed during monsoon season. The third

high values were observed in January at all the stations. Therefore, it is clear from

the data that this nutrient exhibited by and large trimodal seasonal oscillation.

The higher peak of nitrate during monsoon season was recorded by Gupta

et al. (1980) in Nethravati-Gurupur estuary. Nagarajaiah and Gupta (1983)

recorded the bimodal pattern of seasonal distribution with primary peak in June

and secondary peak in April in the brackish water ponds of Nethravati estuary.

Pradeep and Gupta (1988) observed two peaks one in June/July and the other in

December in the brackish water ponds of Mulki estuary. Suresh (1987) observed

the dominant peak in June, smaller peaks during September/December and April

in Nethravati-Gurupur estuary. Sudhir (1990) documented three peaks, one in

March/April, other during June/July and the third in November/December.

Mathew (1994) recorded two major peaks in June/July, October and smaller peaks

in March/April in the same estuary. Tripathi (2002) recorded a primary peak in

April and two smaller peaks in post-monsoon season in Nethravati-Gurupur

estuary. Recently Chandrashekara (2004) observed a primary peak in June/July

and two peaks in post-monsoon season with maximum peak in October month in

Sita-Swarna estuary.

In the present study, although triple oscillation of seasonal variation was

observed at all the stations the primary and secondary peaks varied from one

station to the other. A primary peak of pre-monsoon season was observed at

station 1, 3 and 4. Whereas, the primary peak at station 2 and 5 was observed in

monsoon season.

5.3.2. Phosphate-phosphorous

Dissolved phosphate occurs mainly has inorganic ortho phosphate. This is

one of the major nutrients for primary production in the aquatic environment.

Often phosphate is identified as the nutrient responsible for eutrophication in

confined water. In the present study, the concentration of phosphate in the surface

water ranged from 0.24 to 9.34 µg-at/l (Table 10). In the Nethravati-Gurupur

estuary, Reddy (1982), Suresh (1987), Vedamurthy (1992), Mathew (1994),

Gowda et al. (2001b) and Tripathi (2002) reported values as high as 2.97, 3.50,

2.35, 4.82, 4.32 and 6.31 g-at/l respectively. Chandrashekara (2004) has

recorded phosphate-phosphorous concentration ranging from 0.15 to 9.10 g-at/l

in the Sita-Swarna estuary of west coast of India.

Verlencar (1987) recorded values as high as 2.4 g-at/l, along the estuarine

waters of Goa. The lower phosphate value of 0.11 to 0.56 µ mol/l in Mandovi

estuary was recorded during pre-monsoon season by De’Souza (1999) and the

author has attributed this low concentration to discharge of mining rejects.

Krishna Kumari et al. (2002) recorded phosphate values as high as 8.06 µ mol/l in

Mandovi-Zuari estuary.

Along the east coast, Gouda and Panigrahy (1995) in Rushikulya estuary

documented the values of phosphate in surface water, which range from 0.09 to

1.86 g-at/l. The phosphate concentration in the surface waters of Haladi-Chakra

estuary was found to be slightly higher than that of the values recorded by many

authors in Nethravati-Gurupur estuary, Mulki estuary and Mandovi-Zuari

estuarine complex respectively. However, the present higher value is almost

similar to the higher values obtained by Krishna Kumari et al. (2002) in Mandovi-

Zuari estuary and Chandrashekara (2004) in the Sita-Swarna estuary.

From the Figure 9, it is revealed that the surface water phosphate

concentration exhibited first peak in February at all the stations. The monsoon

primary peak was observed in July at all the stations. During post-monsoon season

phosphate values gradually decreased and reached to a minimum in January. Thus

it can be stated that this nutrient exhibited bimodal seasonal oscillation. However,

Nair et al. (1975) reported the primary peak during late pre-monsoon and early

monsoon and smaller peaks during September and October in Cochin backwaters.

However, Devassy and Goes (1989) recorded the peak phosphate concentration in

October in Mandovi-Zuari estuary of Goa. The present observation is in

agreement with the works of Suresh (1987), Sudhir (1990), Gowda et al. (2001b)

and Tripathi (2002) reported bimodal seasonal oscillation in Nethravati-Gurupur

estuary. However, Chandrashekara (2004) observed higher values of phosphate

concentration but could not get clear-cut seasonal oscillation. The spatial

distribution of this nutrient has revealed higher values at stations situated away

from the confluence region.

5.3.3. Silicate-silicon

Silicate a terregenous nutrient that is generally available in higher

quantities in estuarine environment. In comparison to other nutrients, it is always

present in higher quantity than the absolute requirement of phytoplankton.

However, the silicate might become a limiting factor immediately after the diatom

blooms.

In the present study, silicate in the surface water varied from 0.19 to 91.14

g-at/l (Table 11). In Mulki estuary, Reddy et al. (1985) recorded peak silicate

value of 37.08 g-at/l. While Suresh (1987) and Vedamurthy (1992) in

Nethravati-Gurupur estuary recorded values as high as 134.99 and 157.82 g-at/l

respectively. Teleng et al. (1983) documented the values as high as 57.4 g-at/l in

Kanasgeri backwater along the east coast of India. In the backwater and estuarine

environment of Porto Novo, Ramadhas et al. (1976) recorded a peak value of 71.0

g-at/l and 86.0 g-at/l respectively. Ragothaman and Patil (1995) observed

silicate values in Narmada estuary, which varied from 0.04 to 1.7 g-at/l. Mathew

(1994) recorded 126.0 g-at/l in brackish water ponds of Nethravati estuary. In

the Mandovi estuary, Goa, De’Souza (1999) observed silicate values ranging from

1.25 to 130 µ mol/l .Tripathi (2002) documented silicate concentration, which

varied from 3.84 to 136.44 g-at/l in Nethravati-Gurupur estuary. Chandrashekara

(2004) while working in Sita-Swarna estuary documented the silicate

concentration varying from 0.85 to 136.44 g-at/l. In the present study, the silicate

concentration is lesser than that of the authors worked in various estuaries of west

coast of India. However, the present values were almost nearer to the values

recorded by Ramdhas et al. (1976), Teleng et al. (1983), and Ragothaman and

Patil (1995).

It is evident from the Figure 10, that the silicate concentration exhibited

peaks and trough at every alternate month throughout the period of study.

Therefore, it can be stated that this nutrient did not exhibit any clear cut seasonal

variation. Suresh (1987), Sudhir (1990), Vedhamurthy (1992), De’Souza (1999),

Krishna Kumari et al. (2002) and Chandrashekara (2004) have recorded bimodal

seasonal oscillation in Nethravati-Gurupur, Mandovi-Zuari and Sita Swarna

estuarine complex respectively. From the data, it is evident that the stations

located at and near confluence registered comparatively higher concentration of

silicate than that of the station located away from it.

5.4. Phytoplankton pigments

The micro and macro algae synthesize organic matter through the process

of photosynthesis. In this process, conversion of radiant energy into chemical

energy is intimately dependent upon chlorophyll pigments, which are embedded

in thalakoids of each chromatophore. In great majority of algae accessory

pigments such as caroteins, xanthophylls and phycobilins play a major role in

transferring required wavelength of light to chlorophyll. Many investigators

related chlorophyll of phytoplankton to total organic matter synthesized at any

given time {(Riley et al. (1949) and Ryther (1956)}. It is well known that

chlorophyll contains fat-soluble compounds in the pigment with magnesium at the

center (Yentsch and Scagel 1958). A pigment without magnesium looses the

phyto linkage from the chlorophyll resulting in the formation of phaeophytin. The

caroteins are one of the accessory plant pigments with long hydrocarbon chain

ending in the ring structure (Raymont, 1980). Among the three chlorophyll

pigments (a, b, c) the estimation of active chlorophyll-a directly provides the total

standing crop of any aquatic environment.

5.4.1. Chlorophyll-a

In the present investigation, chlorophyll-a concentration varied from 0.54

to 50.21 mg/m3 (Table 12). Bhattathiri (1976) observed chlorophyll values ranging

from 2.2 to 12.6 mg/m3 in the estuarine waters of Goa. Verlencar (1984) in

Mandovi estuary documented chlorophyll values as high as 11.3 mg/m3. While

Desai et al. (1984) in different estuaries of Gujarat documented chlorophyll-a

values as high as 33.45 mg/m3. In Cochin estuary, Sivadasan and Joseph (1995)

observed chlorophyll-a as high as 70.35 mg/m3. In polluted Bombay harbour

Thana-Bassein creek estuarine complex, Ramaiah and Nair (1998) recorded 3.5

mg/m3of chlorophyll-a. In lower reaches of Vashista estuary, Vijayalakshmi et al.

(1998) documented 3.1 mg/m3 of chlorophyll-a. Krishna Kumari et al. (2002) in

Mandovi-Zuari estuary, observed the chlorophyll-a content which ranged from

0.01 to 4.33 mg/m3. Selvaraj et al. (2003) observed chlorophyll-a values, which

varying from 0.93 to 8.85 mg/m3 in Cochin backwaters.

In Nethravati-Gurupur estuary, Suresh (1987) observed chlorophyll-a

values ranging from trace to 24.63 mg/m3. Mathew (1994) documented values

ranging from 0.12 to 33.1 mg/m3. However, Manjappa (1987) documented

chlorophyll-a value as high as 24.56 mg/m3. In Nethravati-Gurupur estuary,

Gowda et al. (2001b) observed chlorophyll-a values varied between 1.18 and

11.35 mg/m3. Whereas Gupta et al. (2002) recorded value as high as 17.62 mg/m3

in Hangarkatte estuary. Tripathi (2002) observed chlorophyll-a content, which

varied between 0.53 and 20.29 mg/m3. Chandrashekara (2004) while working in

the distribution of phytoplankton in Sita-Swarna estuary observed chlorophyll-a

value in the range of 0.65 to 14.01 mg/l. In the present investigation, the values of

chlorophyll-a are slightly higher than that of the values recorded by earlier

authors.

In Narmada estuary, Gaibhiye et al. (1981) documented chlorophyll values

ranging from 7.8 to 31. 84 mg/m3. In Vellar estuary, Kawabata et al. (1993)

observed chlorophyll-a ranging from 3.6 to 6.5 mg/m3. Santhanam et al. (1994)

while working on the impact of Trichodesmium bloom on the phytoplankton and

productivity, in Tuticorin Bay recorded chlorophyll-a value as high as 535.26

mg/m3.

In the present investigation, higher chlorophyll-a values were observed in

the month of March at all the stations. The second maxima were recorded in

July/August at all the stations. While the post-monsoon peak was observed in

October/November at all the stations. Therefore from the Figure 11, it is evident

that the chlorophyll-a in this region exhibited trimodal seasonal oscillation. The

post-monsoon season was higher than that of monsoon at all stations except at

station 2 where monsoon peak was higher.

In the Cochin backwater, Joseph and Pillai (1975) recorded highest

chlorophyll-a value during post-monsoon season and moderate during monsoon

season. Whereas Gopinathan et al. (1994) observed a single dominant peak during

monsoon in the same environment. Devassy and Goes (1989) observed a

dominant post-monsoon peak in Camburjua and Zuari system of Goa. Suresh

(1987) documented two peak values of chlorophyll-a in June/July and December

in Nethravati estuary. Manjappa (1987) in the coastal waters of Mangalore

recorded dominant peak in pre-monsoon season and smaller peak during post-

monsoon season. Nair (1990) observed a peak value of chlorophyll-a during April

in Edaiyur Sandras estuarine systems at Kalpakam. Mathew (1994) in brackish

water ponds of Nethravati estuary recorded peak value of chlorophyll-a during

monsoon and post-monsoon season.

Gowda et al. (2001b) documented pre and post-monsoon peaks of

chlorophyll-a in Nethravati estuary. Tripathi (2002) observed pre and post-

monsoon peaks of chlorophyll-a in Netharavati-Gurupur estuary. The post-

monsoon peak was more dominant than that of pre-monsoon peak.

Chandrashekara (2004) observed dominant peak in post-monsoon season. In the

present study, the seasonal variation of chlorophyll-a is in agreement with a

variation recorded by Joseph and Pillai (1975), Devassy and Goes (1989),

Manjappa (1987) and Tripathi (2002).

While comparing chlorophyll-a with that of salinity variation it is evident

that the period of high chlorophyll-a content coincided with the period when

mixoeuhaline conditions of water existed in the estuary.

5.4.2. Phaeophytin Appreciable quantities of phaeophytin pigments, a degraded product of

chlorophyll in the present study fluctuated between 0.92 to 61.74 mg/m3 (Table

13). The information on the variation of phaeopigments in space and time in

brackish water environment along both the coast of India is scanty. Sundararaj and

Krishnamurthy (1975) have reported the distribution of phaeopigments in

backwaters and reported increase in phaeopigment levels corresponding to

increase of chlorophyll-a.

In Edaiyur Sandras estuarine system, Nair (1990) observed the same

pattern of relationship between chlorophyll and phaeopigments. Suresh (1987)

and Manjappa (1987) while working in the Nethravati estuary and coastal waters

off Mangalore, have not observed a clear relationship between chlorophyll-a and

phaeopigments in their seasonal variation. Mathew (1994) while working in semi-

enclosed pond of Nethravati estuary observed monsoon, post-monsoon and pre-

monsoon peaks and peak values were as high as 224.28 mg/m3. However, Nayar

and Gowda (1999) documented phaeopigment values to range from 3.02 to 30.52

mg/m3 in Talapady lagoon. Gowda et al. (2001b) recorded phaeopigment values,

which varying between 0.11 and 32.04 mg/m3 in Nethravati estuary. Gupta et al.

(2002) recorded a high value of 24.83 mg/m3in Nethravati estuary, 30.44 mg/m3 in

Pavanje estuary and 28.04 mg/ m3 in Kollur estuary of Dakshina Kannada and

Udupi District.Tripathi (2002) recorded the value as high as 36.56 mg/m3 in

Nethravati-Gurupur estuary. Chandrashekara (2004) observed the values as high

as 27.78 mg/m3 in Sita-Swarna estuary.

In the present study, the seasonal variation of this parameter indicated that

distinct three peaks one during pre-monsoon, the second in monsoon and the last

peak in post-monsoon season. Therefore from the Figure 12, it can be stated that

phaeopigments exhibited trimodal seasonal oscillation. Among the three peaks

post-monsoon peak was predominant at all the stations except at station 2, where

it was in monsoon season. The present values are in agreement with the values

recorded by Mathew (1994) observed monsoon, post-monsoon and pre-monsoon

peaks. However, Tripathi (2002) and Chandrashekara (2004) did not observe

clear cut seasonal variation although they establish a close relationship between

chlorophyll-a and phaeophytin pigments.

5.5. Sediment analysis 5.5.1. Sediment temperature

Sediment temperature is known to influence the chemical characteristics of

interstitial waters, there by determining the occurrence, abundance and

distribution of benthic organisms. Therefore, the sediment temperature in the

present study was recorded as a related parameter of macrobenthos. During the

study period the sediment temperature fluctuated from minimum of 25.5oC to a

maximum of 32.9oC (Table 14).

The minimum and maximum sediment temperature was slightly more than

that of surface water temperature. This kind of sediment temperature distribution

along the Mangalore coast was observed by Reddy (1983), Sahoo (1985), Prabhu

(1992) and Mohan Kumar (1999). Varshney et al. (1983) documented increased

sediment temperature from inshore to offshore region along the coastal waters of

Versova, Bombay. Similarly, increased sediment temperature was observed by

Shanthanagouda (2001) in Nethravati-Gurupur estuary, Nagendra Babu (2004) in

Sita-Swarna estuary and Shiva Kumar (2005) in Mulki-Pavanje estuary

respectively along south west cost of India.

The seasonal distribution of sediment temperature revealed a gradual

decrease in the values during south west monsoon season. In post-monsoon

season, the temperature showing peak in October. While in pre-monsoon season,

it exhibited an increasing trend with peak in May. Thus it is clear from the Figure

13, the sediment temperature in Haladi-Chakra estuarine complex exhibited by

and large bimodal seasonal oscillation. Bhat (1979) and Shanthanagouda (2001)

recorded unimodal seasonal oscillation of sediment temperature in Nethravati-

Gurupur estuary. Whereas Nagendra Babu (2004) observed bimodal seasonal

oscillation with a primary peak in April during pre-monsoon season and

secondary peak in October/November during post-monsoon season. Shiva Kumar

(2005) recorded a trimodal seasonal oscillation of sediment temperature in Mulki-

Pavanje estuary.

The spatial distribution of sediment temperature revealed slightly higher

values at station 1 (confluence) compared to other stations, which are situated in

Haladi-Chakra estuary. However, Shanthanagouda (2001), Nagendra Babu (2004)

and Shiva Kumar (2005) observed greater spatial variation in Nethravati-Gurupur,

Sita-Swarna estuary and Mulki-Pavanje estuary respectively.

5.5.2. Sediment pH

It is well known that pH is single parameter in the interstitial habitat that

can change the form of many chemical parameters, which influence the benthic

organisms. During the present study, sediment pH varied from a lowest of 6.18 to

a highest of 9.19 (Table 15). Jayaraj (1982) and Reddy (1983) while working on

the benthos of South Canara coast documented slightly higher range of pH which

fluctuated from 7.60 to 8.00. Whereas Sahoo (1985) recorded a low of 6.05 and

high of 8.45. Shanthanagouda (2001) documented the sediment pH which ranged

from 6.80 to 8.00 in Nethravati-Gurupur estuary. However, Rajesh et al. (2004)

recorded the mean value of the sediment pH, where values ranged from 5.43 to

6.06 in brackish water impoundments along Nethravati estuary, Dakshina

Kannada. Nagendra Babu (2004) observed the sediment pH, which fluctuated

from 6.70 to 7.90 in Sita-Swarna estuary Udupi. Shiva Kumar (2005) recorded the

sediment pH of 5.6 to 8.26 in Mulki-Pavanje estuarine complex, Dakshina

Kannada. Varshney et al. (1983) documented gradual increase of sediment pH

from inshore to offshore regions in the coastal waters of Versova, Bombay.

Nasnolkar et al. (1996) documented sediment pH in Mandovi-Zuari estuary, Goa,

which ranged from 7.13 to 7.79. Along the east coast of India, Chandran et al.

(1982) recorded mud pH, which ranged from 6.74 to 8.10 in Vellar estuary. The

sediment pH recorded in the present study is in agreement with the studies carried

out in estuaries and bays along both the coast of India except with the

observations of Rajesh et al. (2004).

The seasonal distribution of sediment pH revealed higher values in the pre-

monsoon and post-monsoon season compared to lower values during the monsoon

season. This indicated that the increased freshwater flow during monsoon could

have been the possible factor to bring down pH values to almost slight acidic

condition. Whereas during the non-monsoon season the building up of the salinity

due to increased incursion of saline water could be the causative factor for

maintaining alkaline condition during post and pre-monsoon season. Therefore

from the Figure 14, it could be stated that the sediment pH exhibited lower values

in monsoon and higher values in post and pre-monsoon season.

Reddy (1983) and Sahoo (1985) observed a unimodal seasonal fluctuation

in the Nethravati-Gurupur estuary and Talapadi lagoon respectively. Nasnolkar et

al. (1996) observed slightly alkaline condition of sediment during monsoon and

post-monsoon season in Mandovi estuary, Goa. Mohan Kumar (1999)

documented unimodal seasonal oscillation in the coastal waters off Chitrapur,

Dakshina Kannada. However, Shanthanagouda (2001) observed bimodal seasonal

oscillation in Nethravati-Gurupur estuary. Nagendra Babu (2004) observed

unimodal seasonal oscillation in Sita-Swarna estuary, Udupi. Shiva Kumar (2005)

observed no distinct seasonal clear-cut peaks of sediment pH in Mulki-Pavenje

estuarine complex, Dakshina Kannada.

The spatial variation in the sediment pH during the present study indicated

by and large the uniform variation at all the stations. The higher values are

recorded at confluence (station 1) and lower values at Haladi estuary (station 2

and 3) and moderate values in Chakra estuary (station 4 and 5). The lower values

recorded in monsoon season.

5.5.3. Sediment texture

From the perusal of the literature, it is evident that textural characteristics

of sediment are the important parameters, which influence the quality and quantity

of benthos. Moreover, with meiofaunal species being smaller in size might be

expected to be more sensitive to changes in textural characteristics of the sediment

(Parsons et al. 1977). Further, the type of sediment will also determine

concentration of nutrients.

During the present investigation, the sand fraction dominated at all the

stations in all the months except in December at station 3 in Haladi estuary with

only 42.70% contribution of sand, followed by silt and the clay and it varied in

space and time (Table 16). However, silt fraction was found to be dominating at

almost all the stations during monsoon season. However, in pre-monsoon and

post-monsoon season the clay percentage was found to be lesser than silt

percentage and sand percentage. Since the sediment texture in the environment

depends on the topography of the location, the strength of riverine and tidal flow.

The composition of sediment indicated that the sediment of Haladi-Chakra

estuarine complex is greatly dominated by Sand > Silt > Clay. This could be due

to the lesser riverine strength, which is responsible for clay settlement and more

the tidal strength from seaward tide is more that could be the reason for the greater

percentage of sand in all most all the stations.

Ansari et al. (1986) while investigating on macrobenthos of central west

coast of India observed higher percentage of sand with little or no clay in the

Malpe Bay and Mangalore coast. Reddy (1983) reported dominance of sand

followed by silt and clay in Nethravati-Gurupur estuary. Ramachandra et al.

(1984) documented the greater dominance of sand and equal contribution of silt

and clay in the sediments of Mulki estuary. Seralathan (1993) in the Cochin

harbour observed higher percentage of sand, but silt and clay had equal

dominance in the sediment. Nair et al. (1993) while studying the sediment

characteristics of Cochin estuary stated that sediment texture in the estuary gets

influenced by the monsoon and mixing process in the environment. Prabhu et al.

(1993) observed dominance of sand, which gradually changes to clayey silt as the

distance, increased from the shore along the coast of Gangoli, Dakshina Kannada.

Varying characteristics of sand, silt and clay of sediments of Marmagoa harbour,

Goa were documented by Ansari et al. (1994).

Nasnolkar et al. (1996) although observed dominance of sand in the

sediment during monsoon and post-monsoon season they have documented higher

percentage of silt and clay at some stations during monsoon and post-monsoon

season in Mandovi estuary, Goa. Badarudeen et al. (1998) observed highest

percentage of sand in the sediment of Kannur mangrove region south west coast

of India. Prabhu et al. (1997) observed clayey nature of sediment of Honnavara,

North Karnataka district. Shanthanagouda (2001) while working in Nethravati-

Gurupur estuary documented sediment texture, which varied between stations and

seasons.

Mohan (2000) while working on sediment transport mechanism in Vellar

estuary observed predominance of sand at the head of the estuary with silt and

clay as subordinate constituents. Greater percentage of sand followed by silt and

clay was observed by Kailasam and Siva Kami (2004) in the sediment collected

from Tuticorin Bay, east coast of India. Nagendra Babu (2004) observed the sand

faction dominated at all the stations in all the months followed by silt and clay.

Shiva Kumar (2005) reported higher percentage of sand followed by clay and silt

in Mulki-Pavenje estuarine complex.

The present data on sediment texture, while comparing with that of the

other study, it becomes evident that every estuary exhibit different types of

sediment texture in different seasons. This is because the texture of the sediment

not only depends on season, proximity to the sea, magnitude of mixing and

activity at the adjoining coasts but also on terrigenous and anthrapogenic input.

From the data gathered on sediment characteristics and benthic population, it

becomes clear that the contribution of silt to the total sand fractions throughout the

study period at station 4 could be the favorable environment for supporting higher

density of benthic organisms.

5.5.4. Sediment organic carbon

Organic carbon in sediment is basically derived from within the ecosystem

and also by transportation of leaf and eroded materials (Likens, 1972). Sediments

rich in organic content with an active microbial flora form an important food

source for a majority of benthic organisms. Further, it is well known that sediment

texture will determine the total organic matter and inturn influence the abundance

and occurrence of benthic organisms.

Organic carbon in the sediment during the study period varied from 0.03 to

1.67% (Table 17). Ramachandra (1981) documented organic carbon in Mulki

estuary, which varied from 0.01 to 1.65 %. Similar range of organic carbon was

recorded by Bhat (1979), Reddy (1983) and Shanthanagouda (2001) in

Nethravati-Gurupur estuary, Nair et al. (1983) in Ashtamudi estuary and

Alagarsamy (1991) in Mandovi estuary, Goa. However, Nasnolkar (1996)

recorded sediment organic carbon as high as 32.77 mg C/g in Mandovi estuary,

Goa. Bijoy Nandan and Azis (1996) documented 137.09 mg C/g in the retting

areas of Kadinamkulam estuary.

Total organic carbon of sediment of Beypoor estuary (south west coast of

India) was observed by Nair and Ramachandran (2002) that varied from 0.10 to

6.54%. Along the east coast Chandran et al. (1982) documented sediment organic

carbon as high as 14.88 mg C/g in Vellar estuary. While Sasamal et al. (1986)

documented sediment organic carbon percentage, which varied between 0.59 and

4.12%. However, Prabha Devi (1994) observed as high as 27.8 mg C/g in

Coleroon estuary during post-monsoon season. Kumary et al. (2001) documented

sediment organic carbon, which varied between 2.4 and 83.3 mg C/g in Poonthura

estuary.

The seasonal variation of organic carbon revealed primary peak in March

and it reaches maximum of 1.67% in July with very low values in April of 0.03%.

The values gradually increased and reached the peak in July during monsoon

season and further the values exhibited slight increase up to 1.5% during post-

monsoon season of October. Therefore from the Figure 18, it becomes evident that

the sediment organic carbon in this estuary exhibited a trimodal seasonal

oscillation with one pre-dominant peak in monsoon and two smaller peaks in pre

and post-monsoon season. Nasnolkar et al. (1996) while working in Mandovi

estuary, Goa, observed peak values of sediment organic carbon from July to

September during monsoon season. However, in Nethravati-Gurupur estuary

higher values during April/November/December was observed by

Shanthanagouda (2001). Nagendra Babu (2004) observed the organic carbon in

the range of 0.01% to 1.84% exhibited a trimodal seasonal oscillation with one

pre-dominant peak in monsoon season and two smaller peaks in pre and post-

monsoon season. Shiva Kumar (2005) reported the organic carbon in the range of

0.06% to 1.05% in Mulki- Pavenje estuarine complex, Dakshina Kannada.

The spatial distribution of organic carbon during the study revealed

comparatively higher percentage at station 5 and station 4 in Chakra estuary than

that of station 1 at confluence and station 3 and station 2 located in Haladi estuary.

From the data gathered, it becomes clear that at all the stations during the

period of study the organic carbon was well bellow 3%. Therefore, it could be

stated that this estuarine sediment does not fall under the category of polluted

environment. This perhaps is due to existence of vigorous oxidation activity in the

sediment.

5.6. Phytoplankton 5.6.1. Qualitative distribution

In the present investigation the total number of phytoplankton cells varied

from 14524 to 20355607 cells/m3 (Table 18 to 22).

Perumal et al. (1999) observed high populatation density of phytoplankton

to the extent of 1,99,600 cells/l in Vellar estuary. Tripathi (2002) observed more

than 1,19,00,000 cells/m3 in Nethravati-Gurupur estuary. In Cochin backwaters,

Selvaraj (2003) documented 2,35,000 cells/l. Whereas Chandrashekara (2004) has

documented more than 1,16,00,000 cells/m3 in Sita-Swarna estuary. However in

the present investigation, the total number of phytoplankton cells accounted was

2,03,55,607 cells/m3, which were almost similar to that of the values recorded by

Perumal et al. (1999) and Selvaraj (2003).

The peak abundance of phytoplankton was observed both in pre-monsoon

season and post-monsoon season with a small rise at the end of pre-monsoon and

monsoon season. However, during monsoon and early post-monsoon the number

of cells were minimum. From the Figure 19, it is evident that the total

phytoplankton cells exhibited by and large bimodal seasonal oscillation. However,

Tripathi (2002) and Chandrashekara (2004) observed multimodal seasonal

oscillation in Nethravati-Gurupur and Sita-Swarna estuary respectively.

5.6.1.1. Cyanophyceae

Investigations on the occurrence and distribution of blue green algae have

been carried out by many scientists. Many of the species of blue green algae are

known to fix atmospheric nitrogen and exert influence on nutrient budget of the

water body. Trichodesmium sp., Oscillatoria sp. and Lyngbya sp. are the dominant

forms of cyanophycea in marine and estuarine environment. Instances of

discoloured water phenomenon due to Trichodesmium sp. in Indian waters have

been studied by Bhimachar and George (1950), Prabhu et al. (1965) and Devassy

et al. (1978) Ramesha et al. (1992) and Ronald (2001).

In the present investigation, the Cyanophyceae consisted of various species

belonging to the genera Anabaena, Lyngbya, Merismopedia, Microcystis, Nostoc,

Osillatoria, Spirulina and Trichodesmium. Among blue green algae

Trichodesmium, Osillatoria and Merismopedia occurred frequently with greater

numbers, whereas other forms occurred less frequently with low numbers.

Kumar (1984) while working on the seasonal distribution on the plankton

in the coastal waters of Mangalore documented only one species of blue green

algae, namely Trichodesmium erythraeum with the greater abundance. Further, the

author documented its greater influence on the total biomass of phytoplankton.

Pradeep (1980) observed the dominance of Merismopedia in brackish water ponds

of Mulki estuary, Dakshina Kannada. Mathew and Nair (1980) observed the

dominance of Cyanophyceae in Ashtamudi estuary, Kerala. Reddy (1982)

recorded Anabaena, Pharmidium, Microcystis and Oscillatoria in the water of

Mulki estuary. Whereas Perumal et al. (1999) observed the dominance of

Trichodesmium erytherium in Vellar estuary. Tripathi (2002) and Chandrashekara

(2004) observed the dominance of Trichodesmium, Oscillatoria and

Merismopedia in Nethravati-Gurupur estuary and Sita-Swarna estuary of

Dakshina Kannada and Udupi districts respectively.

In the present study, the blue green algae consisted of Oscillatoria,

Trichodesmium and Merismopedia which were abundant during pre-monsoon

season at all the stations except at station 3 (Table 18 to 22 and Figure: 20 to 22).

During monsoon season, stations located at and near the confluence recorded

moderate numbers of Oscillatoria, Trichodesmium and Merismopedia. In addition

to these Nostoc, Spirulina were present in low numbers. During post-monsoon

season, Oscillatoria along with Merismopedia formed the bulk of the blue green

algae. From the data collected, it becomes clear that the greater abundance of blue

green algae was observed only when salinity was higher during pre and post-

monsoon season. During low saline regime the species of Spirulina and Lyngbya

were found along with oscillatoria in low numbers.

Kumar (1984) observed the presence of Trichodesmium sp. almost

throughout the year in coastal water of Mangalore. Devassy and Goes (1988)

observed the abundance of Trichodesmium during pre and post-monsoon season in

Mandovi-Zuari estuarine complex. While Puranik (1990) documented higher

abundance of Trichodesmium during later half of pre-monsoon season in

Nethravati-Gurupur estuary, Mangalore. In the same area, Ronald (2001)

documented the greater abundance of Trichodesmium during post-monsoon

season and Gupta et al. (2002) recorded the dominance of Trichodesmium only

during the pre-monsoon in the same environment. Eswari and Ramani Bai (2002)

observed the dominance of Trichodesmium and Oscillatoria during non-monsoon

months in Adyar estuary. Tripathi (2002) observed the abundance of

Trichodesmium when the salinity was high and the presence of Lyngbya and

Merismopedia when salinity was low in Nethravati-Gurupur estuary. The

dominance of Microcystis, Nostoc and spirulina during the monsoon months and

the pre-ponderance of Trichodesmium and Oscillatoria were observed by

Chandrashekara (2004) in Sita-Swarna estuary.

In the present study, the occurrence and seasonal distribution of blue green

algae was found to be similar to that of the observation made by Pradeep and

Gupta (1988) in brackish water ponds of Mulki estuary and Chandrashekara

(2004) in Sita-Swarna estuary.

5.6.1.2. Chlorophyceae In the present investigation, several species of green algae belonging to 16

genera were recorded. Among them the Ulothrix, Mougeotia, Closterium,

Pediastrum, Staurastrum, Sphaerocystis, Dinobryon and Zygnema occurred more

frequently with fairly good numbers (Table 18 to 22).

Mathew and Nair (1980) recorded the abundance of Spirogyra, Desmidium

and Pediastrum during monsoon and early post-monsoon season in Ashtamudi

estuary, Kerala. Reddy (1982) documented presence of Mougeotia, Pediastrum

and Spirogyra during the early part of monsoon season in Mulki estuary,

Dakshina Kannada. However, Patil (1987) documented the presence of

Agmerellum during pre-monsoon season and Pediastrum during post-monsoon

season in Nethravati-Gurupur estuary. Joseph and Pillai (1975) and Patnaik and

Sarkar (1976) have observed higher number of green algae during the monsoon

season in different estuaries of India. Puranik (1990) has recorded the dominance

of Spirogyra, Pediastrum, Eudorina and Volvax during monsoon season in

Nethravati estuary, Dakshina Kannada. Gowda et al. (2001c) observed the

dominance of Spirogyra, Ulothrix, Zygnema and Mougeotia during monsoon and

early part of post-monsoon season in Nethravati and Gurupur estuary. Eswari and

Ramani Bai (2002) documented 8 species of green algae in Adyar estuary and 4

species in Cooum estuary. Chandrashekara (2004) observed the dominance of

Closterium, Zygnema, Desmidium, Spirogyra, and Microspora in Sita-Swarna

estuary, Udupi.

In the present study except at station located at the confluence (station 1),

in remaining four stations Ulothrix was not only found in greater abundance but

also occurred more frequently, followed by Mougeotia, Pediastrum, Closterium,

Staurastrum and Zygnema.

The seasonal variation of total Chlorophyceae in the present study revealed

a dominant peak during monsoon season followed by secondary peaks in post-

monsoon season and a small rise in pre-monsoon season. It is only at station 1,

located at the confluence recorded a primary dominant peak in pre-monsoon

season followed by a small rise in monsoon and post-monsoon season. Therefore

from the data collected (Figure: 23 to 25), it can be stated that in Haladi-Chakra

estuary the abundance of green algae occurred more during monsoon season

followed by post-monsoon season. The seasonal variation observed in present

study is in agreement with the studies carried out by Mathew and Nair (1980),

Gowda et al. (2001c), Tripathi (2002) and Chandrashekara (2004).

5.6.1.3. Bacillariophyceae

In the present investigation, several species of Bacillariophyceae belonging to

26 genera were identified and numerical estimation have been made. The list of

26 genera of diatoms was presented in Table (18 to 22). Further the forms,

which occurred more frequently with greater abundance, have been depicted

graphically (Figure: 26 to 30). It is clear from the data that Chlorophyceae,

Cyanophyceae and Dinophyceae formed the bulk of phytoplankton community

next to Bacillariophyceae.

Mohanty (1975a) in Chilka lake and Joseph and pillai (1975) in Vellar

estuary have recorded the dominance of diatom during non-monsoon season.

Chandran (1985) and Mani et al. (1986) also observed greater abundance of

diatom in Vellar estuary. Mishra and Panigrahy (1995) in Bahuda estuary,

documented greater numbers of cell count of diatoms. Perumal et al. (1999)

observed greater abundance of diatoms in Vellar estuary. Similar dominance of

diatoms was also observed by Eswari and Ramani Bai (2002) in Adyar and

Cooum estuary.

Gopinathan (1975), Joseph and Pillai (1975), Mathew and Nair (1980),

Jayalakshmy et al. (1986) and Selvaraj et al. (2003) recorded dominance of

diatom during non-monsoon season in estuaries and backwaters of Kerala. In the

brackish water and estuarine environment of Dakshina Kannada, Nagarajaiah

(1980), Reddy (1982), Patil (1987), Puranik (1990), Bhattacharjaya (1991),

Gowda et al. (2001c), and Tripathi (2002) and Chandrashekara (2004) observed

the dominance of Bacillariophyceae in their investigation. While studying the

plankton distribution of Kali estuary, Karwar, Kusuma et al. (1988) recorded the

dominance of diatoms during pre and post-monsoon season.

A similar dominance of diatoms was observed by Devassy and Bhargava

(1978), Devassy (1983), Devassy and Goes (1988) and Redekar and Wagh (2000)

in Mandovi-Zuari estuary. Ramaiah et al. (1998) recorded the dominance of

diatoms in Thana-Bassein creek estuarine complex. Further, Krishnakumari et al.

(2002) while studying the primary productivity of Mandovi Zuari estuary of Goa,

recorded the dominance of diatoms.

In the present investigation at station 1 located in the confluence, species

of diatom belonging to 24 genera such as Biddulphia, Nitzschia, Coscinodiscus,

Ditylum, Rhizosolenia, Melosira, Chaetoceros, Campylodiscus, Pleurosigma,

Streptothecae and Fragillaria occurred more frequently with greater dominance.

During pre-monsoon season, the bulk of diatoms mainly consisted of Biddulphia,

Nitzschia, Coscinodiscus, Chaetoceros and Ditylum and these were responsible

for forming a primary peak in March. A smaller peak in May was formed mainly

due to higher numbers of Coscinodiscus, Biddulphia and Ditylum. In the monsoon

season, the diatoms such as Coscinodiscus, Rhizosolenia and Melosira formed the

monsoon peak. While during post-monsoon season, the Coscinodiscus,

Chaetoceros, Nitzschia, Ditylum, Fragillaria, Rhizosolenia and Melosira formed

the post-monsoon peak in November/December. From the data gathered (Table 18

to 22, and Figure: 26), it is evident that the diatoms exhibited by and large a

trimodal seasonal oscillation. The pre-monsoon peak was dominant than that of

the other peaks not only from the point of view of numerical abundance but also

richness of the diversity. A similar trimodal seasonal oscillation was observed at

stations located at confluence of Nethravati-Gurupur estuary and Sita-Swarna

estuary by Tripathi (2002) and Chandrashekara (2004) respectively.

At station 2 and 3, located in Haladi-Chakra estuary exhibited a primary

peak of diatoms in the month of February and March and species like Biddulphia,

Coscinodiscus, Cyclotella, Ditylum, Nitzschia, Pleurosigma along with

Rhizosolenia and Thalassiothrix, formed the bulk of this group. During monsoon

season, the diatoms such as Coscinodiscus, Melosira and Nitzschia were present

in moderate numbers especially from June to August and exhibited a monsoon

spurt along with Biddulphia and Pleurosigma in the month of September. During

post-monsoon season, they occurred with low to very low values during October

and November, the diatoms of this region exhibited post-monsoon peak during

December/January (Figure: 27 and 28). The peak was found to be consisting of

mainly Biddulphia, Coscinodiscus, Chaetoceros, Nitzschia, Pleurosigma along

with Rhizosolenia and Thalassiothrix. It is interesting to note that smaller cells of

Chaetoceros and Rhizosolenia were abundant in station 3 than that of station 2. So

this variation could be due to the impact of tides on small cells of diatoms.

Tripathi (2002) and Chandrashekara (2004) in the Nethravati-Gurupur

estuary and Sita-Swarna estuary observed bimodal seasonal oscillation

respectively. Further, they also recorded relatively greater number of diatoms at

stations situated away from the confluence. Similar spatial distribution was

observed in Haladi estuary.

At station 4 and 5, located in Chakra estuary exhibited pre-monsoon peak

in March and May. The bulk of the diatoms consisted of mainly Biddulphia,

Coscinodiscus, Chaetoceros, Ditylum, Melosira, Nitzschia and Pleurosigma.

During monsoon season especially between June and August the

composition of diatoms formed mainly of Biddulphia, Coscinodiscus, Ditylum,

Nitzschia, Pleurosigma and Campylodiscus with low to moderate numbers.

However, these diatoms along with Asterionella, Melosira, Cyclotella and

Streptotheca formed a monsoon peak in September. The post-monsoon peak in

Chakra estuary was observed in the month of December and January. This peak

was mainly consisted of Biddulphia, Chaetoceros, Coscinodiscus, Ditylum,

Pleurosigma, Nitzschia along with Fragillaria and Thalassiothrix. Therefore from

the data (Figure: 29 to 30), it is evident that the diatoms exhibited by and large a

trimodal seasonal oscillation by ignoring small peak, which was observed in May.

The numerical abundance in whole study region revealed greater

abundance and richness of diatoms in Haladi estuary followed by confluence and

Chakra estuary. This variation could be due to greater number of sand bars and

small mangrove islands in the Haladi riverine stretches. However, Tripathi (2002)

and Chandrashekara (2004) recorded an abundance of diatoms at stations located

near the confluence.

Nagarajaiah (1980), Reddy (1982), Puranik (1990), Gowda et al. (2001c)

and Tripathi (2002) observed bimodal seasonal oscillation of diatoms in

Nethravati-Gurupur estuary. However, Devassy and Bhargava (1978) in Mandovi-

Zuari estuary and Patil (1987) in Nethravati-Gurupur estuary observed trimodal

seasonal oscillation. It is interesting to note that Chandrashekara (2004) observed

trimodal oscillation of diatoms in Sita estuary and bimodal oscillation in Swarna

estuary.

In Kali estuary, Kusuma et al. (1988) observed bimodal cycle of yearly

abundance one during the pre and the other during post-monsoon periods.

Ramaiah and Nair (1998) in Bombay harbour-Thana and Bassein creek estuarine

complex observed greater abundance of diatoms during non-monsoon season.

However, Mathew and Nair (1980) observed primary peaks of phytoplankton

during monsoon season in Asthamudi estuary, Kerala. It is interesting to note that

a species of diatom belonging to genus Campylodiscus was recorded most of the

time at all the stations during pre-monsoon, monsoon and post-monsoon season

with smaller numbers. This species of diatom was first time recorded by Puranik

(1990) in Nethravati-Gurupur estuary, west coast of India.

5.6.1.4. Dinophyceae Studies on the occurrence and distribution of dinoflagellates are of great

value in fishery research, as several of these species are known to react to the

changes of the properties of water and hence used as indicator of water masses

and their movement. Further, various dinoflagellates are known to cause

discoloration of water towards red, green and yellow. While we have not much

information on the distribution of dinoflagellates in Indian waters, the systematic

studies on the seasonal and temporal distribution of dinoflagellates in estuarine

environment are scanty. In the present investigation, several species of

Dinophyceae belonging to 5 genera such as Ceratium, Peridinium,

Periperidinium, Noctiluca and Dinophysis were recorded (Table 18 to 22). Among

them Ceratium, Peridinium and Periperidinium were common and abundant.

Joseph and Pillai (1975), Santhanam et al. (1975) and Sundararaj and

Krishnamurthy (1975) have investigated the occurrence and distribution of

Dinophyceae in estuarine and coastal waters of India. The seasonal and temporal

variations of Dinophyceae in the estuaries of Dakshina Kannada coast were

observed by Nagarajaiah (1980), Pradeep (1980), Reddy (1982), Patil (1987),

Katti et al. (1988), Puranik (1990), Tripathi (2002) and Chandrashekara (2004).

The seasonal variation of Dinophyceae in station 1 located at confluence

indicated two peaks in March and May, which were mainly constituted by

Ceratium, Peridinium and Periperidinium. Ceratium occurred smaller numbers

formed a smaller monsoon peak from August. While post-monsoon peak was

observed in November/January, which mainly constituted by Ceratium and

Peridinium. Therefore from the data (Figure: 31 to 33), it is evident that

dinophyceae at this station exhibited by and large a tetra modal oscillation.

At station 2, located in Haladi estuary which is away from confluence

registered dominant peak in March consisting of Peridinium and Periperidinium

only and small peak in May which was mainly constituted of Ceratium,

Peridinium and Periperidinium. During monsoon season, the dinoflagellates were

present in meager numbers without exhibiting any peak. Noctiluca occur in

moderate number in September month. While in post monsoon season, a small

peak was observed in January, which consisted of only Peridinium. Therefore, it

can be stated that Dinophyceae at this station exhibited trimodal seasonal

oscillation.

At station 3, which is located nearer to the confluence, Dinophyceae

consisting of Ceratium, Peridinium and Periperidinium exhibited a clear cut

trimodal seasonal oscillation with peaks in March, May and January. Noctiluca

occur in higher number in September month.

At station 4, which is located in Chakra estuary the Dinophyceae

consisting of Ceratium and Peridinium exhibited a dominant peak in May. The

monsoon peak consisted of Ceratium, Noctiluca, Peridinium and Periperidinium,

which formed the peak in September. A predominant peak of Ceratium and

Peridinium formed in the month of December/January. Therefore, it can be stated

that the dinoflagellates at this station exhibited by and large a trimodal seasonal

oscillation.

At station 5, dinoflagellates consisting of Ceratium and Peridinium formed

the peaks of pre-monsoon, whereas only Ceratium was present in September

month in small numbers, while Ceratium and Peridinium formed the peak of post-

monsoon season in December.

The seasonal distribution of Dinophyceae in the region of study by and

large exhibited trimodal seasonal oscillation with two peaks in pre-monsoon

season and small peak in monsoon and post-monsoon season. The spatial

distribution revealed greater diversity richness at the confluence and stations

situated in Haladi estuary when compared to that of Chakra estuary.

While comparing the distribution of Dinophyceae with salinity and

temperature, it is evident that the population abundance of this group coincided

with the higher temperature and salinity regime of the year. Joseph and Pillai

(1975) stated that high temperature and salinity are favorable for better growth

and sustainance of dinoflagellates. Several workers such as Mathew and Nair

(1980), Reddy (1982), Kumar (1984), Patil (1987), Puranik (1990), Gowda et al.

(2001c) and Selvaraj et al. (2003) have recorded high concentration of

dinoflagellates in the estuaries and backwaters of Karnataka and Kerala during

pre-monsoon season. The present observation is in agreement with the above. The

smaller and secondary peak during post-monsoon season coincided with the

stepping up trend in salinity.

Kumar (1984), Patil (1987), Ramesh (1989), Puranik (1990) and Tripathi

(2002) observed the dominance Ceratium furca, C. tripos and C. extensum in the

estuarine and coastal waters of Dakshina Kannada. Same species were also

observed in the present investigation. Among them Ceratium furca dominated

through out the pre-monsoon season. A detailed study was carried out by

Ilangovan (1987) on the diversity and distribution of Dinophyceae in Vellar

estuary, which revealed the dominance Ceratium furca, C. tripos and C. extensum.

In the present study the bulk of dinoflagellates consisted of Ceratium,

Periperidinium, Peridinium and Noctiluca. Among the three species of Ceratium,

Ceratium furca was dominant followed by C. tripos and C. extensum. Similar

dominance of Ceratium furca was observed by Tripathi (2002) in Nethravati-

Gurupur estuary and Chandrashekara (2004) in Sita-Swarna estuary.

The relationship between salinity and total phytoplankton counts revealed

greater abundance of phytoplankton in mixoeuhaline condition of water during

pre-monsoon season. During post-monsoon season, the abundance with moderate

numbers coincided with polyhaline condition. The spatial distribution revealed a

greater abundance of total phytoplankton at station 2 in Haladi estuary and station

1 at confluence region during both pre and post-monsoon season (Figure: 60).

During pre-monsoon season, the higher density of phytoplankton was

found to be coincided with mixoeuhaline condition of water, where the salinity

was more than 30 ppt and less than the adjacent seawater. Whereas during post-

monsoon season, the peaks during December and January was found to be

coincided with holohaline condition, where salinity ranged between 11 ppt and 30

ppt (Figure: 60). In the present study most of the forms, which have exhibited

peak abundance during pre-monsoon season were also found to be exhibiting

another peak during post-monsoon season. Therefore, it is clear that mixoeuhaline

condition is optimum for the vigorous growth of phytoplankton in this estuary.

However, few forms were found to tolerate polyhaline condition which existed

during later half of monsoon season and post-monsoon season. Qasim (1980)

observed higher density of diatoms in the salinity ranges of 10-20 ppt in Cochin

backwater. Patil (1987) and Puranik (1990) documented abundance of diatom

cells in mixoeuhaline condition in Nethravati-Gurupur estuary.

The relationship between Phosphate-phosphorus and total phytoplankton

cells and Nitrate-nitrogen and total phytoplankton cells revealed inverse

relationship (Figure: 61 and 62).

The lower concentration of phosphate, which also coincided with greater

abundance of phytoplankton (Figure: 61), suggests that the low values of

phosphate during the pre-monsoon season could also be due to greater utilisation

of this plant nutrient.

The lower concentration of nitrate, which coincided with greater abundance of

phytoplankton, suggests that the low values of nitrate during the pre-monsoon

season could be due to greater utilisation of this plant nutrient. During

monsoon season, nitrate concentration was high compared to total

phytoplankton cells because lower numbers of phytoplankton cells were unable

to utilize the higher concentration of nitrate nutrient. However, higher

concentration of nitrate and moderate density of phytoplankton during post-

monsoon season could be due to poor utilization of nitrate and high input of

nitrate (Figure: 62).

Similar relationship between phosphate and diatom cell numbers were

observed by Puranik (1990), Gowda et al. (2001c) and Tripathi (2002) in

Nethravati-Gurupur estuary. In the present investigation, relationship between

chlorophyll-a and total phytoplankton cells could not be established. Suresh

(1987), Mathew (1994), Tripathi (2002), and Chandrashekara (2004) did not

observe any relationship between chlorophyll-a and phytoplankton.

5.7. Zooplankton Zooplankton forms an important and integral component of ecosystem by

virtue of its special position in the food chain. The qualitative and quantitative

distribution of zooplankton in space and time are often used as an index for

predicting the fishery potentiality of an environment. According to Shetty et al.

(1961) and Madhupratap (1981) there exists a relationship between zooplankton

and fisheries. The distribution of zooplankton is always patchy and dynamic.

This dynamic nature gets further complicated in an environment like estuaries due

to the influence of tide. Further, the changes in the community structure and

quality of zooplankton reflect the quality of the estuarine waters.

5.7.1. Qualitative distribution 5.7.1.1. Medusae and siphonophores

Hydromedusae form an important ecological category in the plankton

ecosystem because of their specialized position as exclusively carnivores

component in the marine food chain. The hydromedusae greatly contribute to the

volume and biomass of the total plankton.

In the present investigation, only few forms of medusae belonging to

genera Philadilium sp., Eutiama sp. and Erene sp. along with medusoid stages,

benthic hydroids such as Obelia sp. and Cordilophora sp. were observed. The

siphonophores were found to species belonging to the genera Lensia sp. The

number of medusae varied from 01 to 1663 No/m3 and siphonophores from 01

No/m3. From the Table 23 and Figure 34, it is evident that the abundance of

medusae were more in post-monsoon season followed by pre-monsoon and

monsoon season. The higher number was recorded in August at confluence region

(station 1). Whereas siphonophores occurred in meagre numbers only in May.

The abundance of hydromedusae at confluence region dominants the stations

located in Haladi and Chakra estuary. The dominant of medusae at confluence is

due to the greater abundance of these groups in the adjoining coastal waters.

Further, they could easily get transported through the bar mouth during high tide

and entered in the estuarine basin.

Vanucci (1977) while working on the hydromedusae in the Cochin

backwaters observed rich and varied population of hydromedusae during pre-

monsoon season when salinity was relatively higher. However, Bhat (1979)

recorded fairly good number of hydromedusae in December and January in

Gurupur estuary of Dakshina Kannada. Patil (1987) documented higher

abundance of medusae during post-monsoon season in Nethravati estuary and

during pre-monsoon season in Gurupur estuary. While working on zooplankton

ecology, Padmavathi and Goswami (1996) observed higher number of

hydromedusae during pre-monsoon season when temperature and salinity were

higher. Sujatha and Panighray (1999) recorded abundance of medusae during

post-monsoon season in Bahuda estuary (Orissa). The present observation is in

agreement with the observation made by Bhat (1979), Patil (1987) in Nethravati-

Gurupur estuary and Sujatha and Panighray (1999) in Bahuda estuary (Orissa).

However, the study carried out by Santhakumari et al. (1999) revealed abundance

of hydromedusae during post-monsoon season in Dharmatara estuarine system.

Vijay Kumar (2002) observed the abundance of hydromedusae during pre-

monsoon season and moderate number in post-monsoon season in Nethravati-

Gurupur estuary. Vikas (2004) recorded the meager number of hydromedusae in

pre-monsoon season in Sita-Swarna estuary, Udupi.

While comparing the abundance of hydromedusae in present study with

that of Nethravati-Gurupur estuary and Mulki estuary, revealed that the abundance

and distribution of this group along with siphonophores is much lower. This low

density could be due to lesser intensity of transportation from the adjoining coastal

waters or in ability to colonise due to shallowness and high turbidity in this

estuary.

5.7.1.2. Ctenophores Not much data is available on the seasonal distribution of ctenophores in

brackish water environment. However, instance of occurrence have been reported

by several planktonologist working in different brackish waters of India. In the

present study, Pleurobranchia sp. and Mnemiopsis sp. were the sole

representatives of this group. While the Mnemiopsis sp. occurred only in

April/May, the number of which varied from 01 to 02 No/m3 nearer to the bar

mouth, while Pleurobranchia sp. varied from 01 to 02 No/m3 with sporadic

occurance in pre-monsoon season. In post-monsoon season, it occur in December/

January month. It is clear from the Figure 35 and Table 24, that the abundance of

Pleurobranchia sp. was observed maximum during monsoon season. It is

interesting to note that the greater abundance of Pleruobranchia sp. was found in

stations located near to the Haladi estuary and the stations located near the

confluence. The numerical abundance in Chakra estuary was lower when

compared to Haladi estuary. Further, it was observed that the Pleurobranchia sp.

were abundant during monsoon season suggesting that the Pleurobranchia sp.

breed in the adjoining coastal waters immediately after the monsoon season, when

salinity was at moderate levels. Further, the Pleurobranchia sp. occurred in

March/April were all adults with mature gonads.

In Cochin backwaters, Rao et al. (1975) and Madhupratap and Haridas

(1975) recorded higher number of ctenophores. During pre-monsoon season, Bhat

(1979) observed higher number of planktonic carnivore forms during February

and March in Nethravati-Gurupur estuary. However, Patil (1987) recorded fairly a

good number of Pleurobranchia sp. in October and December in the same estuary.

Puranik (1990) documented higher abundance of ctenophores during pre-monsoon

season and were totally absent during post-monsoon season. Peak abundance of

Pleurobranchia sp. in Mandovi-Zuari estuary was observed by Padmavathi and

Goswami (1996) in April. Sujatha and Panigrahy (1999) recorded the occurrence

of ctenophore in April in Bahuda estuary (Orissa). Vijay Kumar (2002) while

studying the distribution of zooplankton in relation to selected hydrographical

parameters in Nethravati-Gurupur estuary observed the greater abundance of

ctenophores in pre-monsoon and post-monsoon season. Vikas (2004) recorded

sporadic numbers of ctenophores throughout the study period and observed

maximum abundance during post-monsoon season in Sita-Swarna estuary, Udupi.

In the present investigation, the period of occurrence and seasonal distribution of

ctenophores was dominated in pre-monsoon and monsoon season found to be

slightly different from that of the study made by different workers in Nethravati-

Gurupur and Mulki estuaries.

5.7.1.3. Chaetognaths and chaetognath larvae

Chaetognaths form an important constituent of marine and brackish water

zooplankton community. Its predatory habit, totally isolated group from main

stream and as an indicator species of water masses has been made it a subject of

intense research.

In the present study, the number of chaetognaths varied from 01 to 51

No/m3 and chaetognath larvae varied from 01 to 1104 No/m3 (Table 25). The

qualitative composition of this group revealed the presence of Sagitta beloti, S.

setosa, S. enflata, S. polchra and Eokonia sp. Among them, most dominant were

S. beloti and S. pulchra. Similar observation was made by Padmavathi and

Goswami (1996) in Mandovi-Zuari estuary, Goa, Sujatha and Panigrahy (1999) in

Bahuda estuary, Orissa, Pattanaik and Sarma (1997) in Chilka lake, Vijay Kumar

(2002) in Nethravati-Gurupur estuary and Vikas (2004) in Sita-Swarna estuary

respectively.

In the present study, chaetognaths were present most of months during

post-monsoon season and were totally absent in April month of pre-monsoon

season except at station 4. In monsoon season, it occur in August and September.

The pre-monsoon peak observed in March except at station 4 and the post-

monsoon peak was noted in October at near confluence and Haladi estuary. The

pre-monsoon peak was more dominant than that of post-monsoon peak in Haladi

estuary. Whereas at confluence and Chakra estuary, the post-monsoon peak was

dominant (Figure: 36). The frequency of occurrence and the numerical abundance

was more at the confluence and Haladi estuary compared to Chakra estuary. In the

Chakra estuary the stations which are located away from the confluence registered

were low numbers of chaetognaths with less frequency.

The chaetognath larvae in the present study occurred almost all the months

accept in April month of pre-monsoon season. The pre-monsoon peak was

observed in February/March, monsoon peak in August (station 1, 3 and 4) and

September month (station 2 and 5), and the post monsoon peak was recorded in

October except at station 1 (Figure: 37). The post-monsoon peak was more

dominant than that of pre-monsoon peak in Haladi-Chakra estuary, but station

near the confluence the monsoon peak was dominant the pre-monsoon and post-

monsoon peaks. From the data gathered, it is known that the stations at the

confluence and the Chakra estuary exhibited higher frequency of occurrence of

chaetognath larvae than that of Haladi estuary. The spatial distribution of

chaetognath and chaetognath larvae in the present study is influenced by

topography of the estuarine basin, which could possible make free flow of tidal

waters to the estuarine region.

Patil (1987) recorded higher number of chaetognaths in Gurupur estuary

than that of Nethravati. Working on the ecology of chaetognaths, Nair and Selva

Kumar (1979) reported presence of more number of species in Zuari estuary than

that of Mandovi-Zuari estuary.

Abundance of chaetognaths during pre and post-monsoon season were

observed by Bhat (1979), Patil (1987), Puranik (1990) and Vijay Kumar (2002) in

Nethravati-Gurupur estuary and Vikas (2004) in Sita-Swarna estuary respectively.

Padmavathi and Goswami (1996) recorded higher abundance of chaetognaths

during pre-monsoon and post-monsoon season in Mandovi-Zuari estuary, Goa.

However in the estuaries along east coast of India, Sarkar et al. (1985) observed

greater abundance during June/July, while Pattanaik and Sarma (1997)

documented greater abundance during July/August. While comparing the

occurrence and distribution of chaetognaths and salinity conditions, it becomes

evident that occurrence and distribution of chaetognaths in these estuaries were

mainly controlled by the intrusion of saline water in to the estuarine region.

Similar observations were made by earlier workers along both the coast of India.

The present observation is in agreement with the works carried out by earlier

authors.

The pre-monsoon abundance of larval forms of chaetognaths suggests the

presence of larval forms in greater numbers in the adjoining coastal waters.

Similar type of larval distribution was observed by Menon et al. (1977) in the

coastal waters of Mangalore, Vijay Kumar (2002) in Nethravati Gurupur estuary

and Vikas (2004) in Sita-Swarna estuary, Udupi respectively.

5.7.1.4. Polychaetes and polychaete larvae

Polychaetes and polychaete larvae forms an important component in

plankton samples of estuarine and coastal waters. Therefore, almost all the

workers documented the occurrence and seasonal distribution while working on

the ecology of estuaries, backwaters and coastal environment.

In the present study, the number of polychaetes fluctuated varied from 01

to 16 No/m3 and polycheate larvae from 01 to 19253 No/m3 (Table 26). The

works carried out by Pillai and Pillai (1975), Madhupratap (1978), Rao et al.

(1985) and Nair et al. (1984) revealed a greater abundance of polychaete larvae

formed an important component in the zooplankton samples collected from

various brackish water environment of Kerala coast. Similar kind of observations

were made by Reddy (1977), Bhat (1979), Nagarajaiah (1980), Reddy (1982),

Patil (1987), Puranik (1990), Vijay Kumar (2002) and Vikas (2004) in various

brackish waters of Dakshina Kannada and Sita-Swarna estuary, Udupi

respectively. The occurrence and distribution of polychaete larvae in Mandovi-

Zuari estuary was studied by Goswami et al. (1979). In Kali estuary, Kusuma et

al. (1988) recorded the occurrence of polychaete larvae. Padmavathi et al. (1997)

recorded small numbers of polycheate larvae in Mandovi-Zuari estuary, Goa.

Srikrishnadas and Ram Moorthi (1982) reported the dominance of polychaete

larvae in Porto Novo waters. While studying on the zooplankton ecology of

Rushikuliya estuary, Gouda and Panigrahy (1995) documented the greater

abundance of polychaete larvae. Mishra and Panigrahy (1999) observed the

presence of polychaete larvae except during flooding season in Bahuda estuary.

In the present study, the seasonal distribution of polychaetes revealed

lesser number in pre-monsoon season. They were completely absent in the month

of June, July and August month of monsoon season. The monsoon peak was

observed in September month at confluence region (station 1). The polychaete

were totally absent during post-monsoon season at station 5. The post-monsoon

peak was observed in the month of October in station 1 and 2 and November in

station 3, but the moderate peak was observed in station 4. The polychaetes in the

present study revealed more numbers at confluence than Haladi and Chakra

estuary. The post monsoon peak was more dominant than pre-monsoon and

monsoon peak except at station 4 (Figure: 38).

In the present study, the polychaete larvae occurred almost throughout the study

except station 4 in July month. The seasonal fluctuation of the larvae revealed

presence of higher numbers during pre-monsoon season with a peak in February at

all stations. The monsoon peak was observed in gradual increase in the month of

June/July and occurred its maximum in August forming the secondary peak. The

post-monsoon peak was observed in January month at all the stations. From the

Figure 39, it is evident that the polychaete larvae exhibited trimodal seasonal

oscillation. The pre-monsoon peak dominant the post-monsoon peak and monsoon

peak in almost all the stations.

It was observed that most of this polychaetes and polychaete larvae are

benthic forms but occurred in the plankton sample because of the shallow nature.

The presence of polychaete larvae throughout the study period suggests the

polychaete of this region breed continuously. Therefore, it could be stated that the

salinity is the prime factor in influencing the breeding periodicity of the

polychaete and polychaete larvae. The maxima during the pre-monsoon season

was observed with the con-comitant (simultaneously) increase in the salinity.

Bimodal seasonal oscillation was recorded by Menon et al. (1977), Eknath

(1978), Patil (1987), Puranik (1990) and Bhat (1979) in the coastal waters and

Nethravati-Gurupur estuary, Mangalore. However, Reddy (1982) in Mulki

estuary could not observe clear-cut seasonal fluctuation of this larvae. Vijay

Kumar (2002) observed higher abundance of this larvae during pre and post-

monsoon season and opined that the salinity is the major factor influencing the

breeding of polychaetes in the coastal waters and Nethravati-Gurupur estuary.

Vikas (2004) documented the seasonal distribution of polychaetes revealed higher

numbers in April exhibiting a single dominant peak during pre-monsoon season.

Similar opinion was drawn by Madhupratap and Haridhas (1975) in Cochin

backwaters and Patil (1987) and Puranik (1990) in Nethravati-Gurupur estuary.

Quality composition of polychaete and polychaete larvae revealed that

most of them were belong to family Neridae, Nepthidae, Glyceridae,

Sabellaridae, Arenicola and Maladanidae. Among them, larvae of Nepthidae,

Neridae and Glyceridae form the bulk of the polychaete larvae throughout the

period of investigation. In the present study, the polychaete and polychaete larvae

were more dominant in stations at and near to the confluence than away from it.

However, Vijay Kumar (2002) observed greater abundance of larvae in Nethravati

than that of Gurupur estuary. Vikas (2004) could not observe any spatial variation

in the Sita-Swarna estuary, Udupi.

5.7.1.5. Cladocera

Cladocerans attracted the attention of many marine biologist and fishery

scientist because of an intimate relationship with pelagic fisheries (Selva Kumar,

1970) and its high reproductive potentiality through parthenogenesis resulting in

spurt at times and total absence at other times (Dellacroce and Venugopal, 1972).

This group was mainly represented by Penilia avirosteris and Evadne tergestina.

In the present study, Penilia sp. number varied from 133 to 28858 No/m3

(Table 27), but they were absent in June/ July month except at station 2. The pre-

monsoon peak was observed in April except at station 5 (March) and station 1

(February). The monsoon peak was observed in August at station 1 and station 2

and September in station 4. At station 3 and 5, it occurs in meager numbers. In

post-monsoon season, the dominant peak was observed in the month of October at

station 1 and 2 and December in station 3, 4 and 5 (Figure: 40). The post-

monsoon peak dominant the pre-monsoon peak. The confluence region registered

the more numbers than Haladi-Chakra estuary.

The Evadne sp. during the present study fluctuated from 133 to 6412

No/m3 (Table 27). The pre-monsoon peak was observed in February at almost all

the stations except at station 2 (April). The monsoon peak was not clearly

exhibited (Figure: 41), but it attains maximum in August (station 1, 2 and 5) and

September (station 3 and 4). The post-monsoon peak was noted in October

(station 1 and 2) where has it attains maximum peak in December (station 3, 4

and 5). During the present study, the Evadne sp. dominant in pre-monsoon and

post-monsoon season. The frequency of occurrence and the numerical abundance

shown at confluence and Chakra estuary were more dominate than that of Haladi

estuary.

Both the species exhibited almost similar trends of occurrence and

abundance, but variation in their dominant peaks. However, the investigations

made by Patil (1987), Puranik (1990) and Vijay Kumar (2002) indicated the

dominance of Penilia avirosteris at salinity values of 3.50 to 31.20 ppt in

Nethravati-Gurupur estuary. Vikas (2004) observed the dominance of Penilia

avirosteris and Evadnae tergestina in Sita-Swarna estuary, Udupi.

Goswami (1992) documented few cladocerans in mangrove ecosystems of

Goa. Gouda and Panigrahy (1995) observed few numbers of cladocerans in

Rushikulya estuary, Orissa. Pattanaik and Sarma (1997) documented sporadic

occuranceof cladocerans in Chilka lake. Chandramohan and Sreenivas (1998)

did not observe cladocerans in the mangrove areas of Gaderu canal south east

coast of India. Mishra and Panigrahy (1999) observed the abundance of

cladocerans in Bahuda estuary, Orissa.

A critical look at the seasonal variation of this group revealed a gradual

increase in number from February to April and total absence in June and July.

Further, the population exhibited second increase in August/September which

gradually increased during later half of post-monsoon season and attain maximum

peak in October/December. From Figure 40 and 41, it is evident that the

cladocerans exhibited bimodal seasonal oscillation. It is interesting to note that

cladocerans were abundant in high saline of waters (February/April) and also

when the salinity was moderate during September/October and December.

Goswami and Selvakumar (1977) reported the dominance of Evadne

tergestina in the salinity range of 0.21 to 1.67, while Penilia avirosteris in the

range of 19.31 to 33.95 ppt. In the present study, Evadne tergestina were

observed in the salinity range of 0.14 to 32.69 ppt and Penilia avirosteris in the

salinity range of 9.49 to 33.00 ppt. The seasonal variation of this group and the

water temperature revealed that the pre-monsoon abundance coincided with

highest water temperature. While post-monsoon abundance coincided with

gradual increase of surface waters. Goswami and Devassy (1991) observed a

wide range of salinity tolerance by cladocerans in Mandovi-Zuari estuary.

Padmavathi and Goswami (1996) reported the abundance of cladocerans at lower

temperature and salinity values in Mandovi-Zuari estuary. In the present study, the

period of occurrence and seasonal distribution of Cladocerans was found to be

similar observation made by Vijay Kumar (2002) and Vikas (2004) in Nethravati-

Gurupur estuary and Sita-Swarna estuary respectively.

5.7.1.6. Cirripede larvae The occurrence of cirripede larvae (nauplius and cypris) would give an

idea about the breeding of barnacle present in the environment. In the present

study, barnacle nauplii varied from 22 to 1657 No/m3 and barnacle cypris ranged

from 01 to 08 No/m3. Cypris larvae were present at two instances one in August

(station 1) and September (station 4). The greater abundance of barnacle nauplii

were present almost all the stations during the pre and post-monsoon season. The

greater abundance of barnacle nauplii were observed in pre-monsoon and post-

monsoon season (Table 28). It is evident from the Figure 42, that the pre-monsoon

peak abundance is different in different months. It shows peaks in February month

(confluence and Haladi estuary) and March month (Chakra estuary). The monsoon

peaks was observed in August month. Whereas the post-monsoon peak was

noticed in October (station 1, 3 and 4) and November (station 2 and 5). Therefore,

it could be stated that the barnacle nauplii exhibited a trimodal seasonal

oscillation. The spatial distribution revealed greater abundance in Haladi estuary

than that of Chakra estuary and confluence region during post-monsoon season.

While during pre-monsoon and monsoon season, the stations at Chakra estuary

exhibited greater abundance than Haladi estuary and confluence region. The low

number in monsoon season was due to low saline conditions.

Patil (1987) recorded a few barnacle nauplii during later part of monsoon

season at station located near the bar mouth in Nethravati-Gurupur estuary.

Similar kind of observation was made by Puranik (1990) in the same environment.

Vijay Kumar (2002) while studying the distribution of zooplankton observed less

number of barnacle nauplii in October/November, when the salinity of water was

very low. Vikas (2004) observed the trimodal seasonal oscillation in Sita-Swarna

estuary, Udupi. The presence of cirripede larvae of greater numbers was observed

in Sita estuary than that of Swarna and confluence during pre-monsoon season.

Bimodal seasonal oscillation of barnacle nauplii was reported by Bhat

(1979), Nagarajaiah (1980), Reddy (1982), Patil (1987), Puranik (1990) and Vijay

Kumar (2002) in the Nethravati-Gurupur estuary and brackish water environment

of Dakshina Kannada.

In the present study, three maxima of barnacle nauplii in pre and post-

monsoon season coincided with high salinity conditions which suggest that the

breeding of barnacles in the area is controlled by salinity conditions of the

environment. From the Figure 42, it is evident that the nauplii were totally absent

in the month of June/July at confluence, due to the dominant of freshwater inflow

from estuary to the confluence region in monsoon season. The rich abundance of

barnacle nauplii throughout the season is influenced by availability of right type of

food for the nauplii and recruitment to the estuary from adjoining coastal waters.

5.7.1.7. Copepods

In the present investigation, copepods formed the bulk of the total

zooplankton and also present throughout the period of study at all the stations. A

greater abundance of copepods in the plankton sample collected from various

estuaries along east coast of India was reported by Mohan (1977), Baidya and

Choudhury (1984), Mohamed and Rahaman (1987), Sarkar et al. (1986) Sarkar

and Choudhury (1988), Gouda and Panigrahy (1995), Chandra Mohan and

Sreenivas (1998) and Misra and Panigrahy (1999).

Along the west coast, Goswami (1982), Bhat and Gupta (1983),

Nagarajaiah and Gupta (1985), Nair and Azis (1987), Thompson (1991), Nandan

and Azis (1994), Neelam-Ramiaha and Nair (1997), Padmavathi et al. (1997),

Vijay Kumar (2002) and Vikas (2004) recorded the dominance of copepods in the

plankton sample collected from various estuaries.

During the present study, the copepod ranged from 3867 to 180632 No/m3.

It is clear from the Figure 43 and Table 29 that the abundance of copepods in this

estuary was in the month of February/May of pre-monsoon season. During

monsoon season, population density of copepods declined at all the stations and

gradually increased in September. An increasing trend was observed during post-

monsoon season with two small peaks during November/January except at station

1 (October/ January).

A general decline during the period of intense rainfall has been reported in

several estuaries and backwaters of east coast of India. [Sundararaj and Krishna

Murthy (1975), Shanmugham et al. (1986), Sujata and Panigrahy (1996),

Pattanaik and Sarma (1997) and Misra and Panigrahy (1999)]. A similar decline

was observed by mainly workers while studying the distribution of plankton in

various brackish waters environment of Kerala, Dakshina Kannada and Goa. [Rao

et al. (1975), Madhupratap et al. (1977), Nair et al. (1984), Bhat (1979),

Nagarajaiah (1980), Reddy (1982), Patil (1987), Goswami (1983), Puranik (1990),

Tiwari and Nair (1993), Padmavathi and Goswami (1996) and Musthafa (1999)].

The pre-monsoon and post-monsoon abundance is found to be more than

monsoon peaks at almost all the stations during the present study. The September

month dominant the monsoon season.

Silas and Pillai (1975) documented greater abundance of copepods during

pre-monsoon in backwaters of Kerala. Patil (1987) in Nethravati-Gurupur estuary

observed greater abundance during pre-monsoon and moderate abundance in post-

monsoon season. However, Bhat (1979) observed variation in magnitude in pre

and post-monsoon at different stations. Puranik (1990) and Vijay Kumar (2002)

observed greater abundance during pre-monsoon season in the same estuary.

Vikas (2004) observed the pre-monsoon abundance was found to be more than

that of post-monsoon at all most all the stations. In Mandovi-Zuari estuary,

Padmavathi and Goswami (1996) reported greater abundance of copepods during

pre-monsoon season.

In the present investigation, the spatial variation of copepods showed

higher density at stations located away from the confluence. The occurrence and

abundance of copepods in Haladi estuary is more than that of Chakra estuary.

Based on salinity tolerance, copepods can be categorised into three distinct types;

one booming in mixoeuhaline conditions prevailed during pre-monsoon, the

second group thriving in limnetic condition during monsoon season and the third

category affluent polyhaline condition of the water prevailed during post-monsoon

season (Table 29).

Patil (1987), Puranik (1990) and Vijay Kumar (2002) have observed the

two types of copepods; one booming mixoeuhaline condition and the other in

polyhaline conditions in Nethravati-Gurupur estuary.

The quality composition of copepod community revealed the presence of

various species belonging to genera Acartia, Paracalanus, Pseudodiaptomous,

Centrophages, Microsetella and Euterpina. The group Cyclopoidae consisted of

species belonging to Oithona, Corycaeus, Oncae, Cyclops and Diaptomous.

Among the three different forms of copepods, Cyclopoidae and Herpecticoidae

dominated the samples collected during monsoon season. While pre-monsoon

samples contained copepods belong to group calanoidae and cyclopoidae. By and

large, similar composition of copepod population was observed by Patil (1987),

Puranik (1990) and Vijay Kumar (2002) in Nethravati-Gurupur estuary and Vikas

(2004) in Sita-Swarna estuary respectively. Neelam-Ramaiaha and Nair (1997)

recorded dominance of calanoid copepods in Bombay harbour-Thana and Bassein

creek west coast of India. Similar dominance of calanoid copepods in Bahuda

estuary was observed by Mishra and Panigrahy (1996). Mohamed and Rahman

(1987) observed greater abundance of Oithona sp. throughout the year in Agniar

estuary Tamilnadu. Gaughan and Potter (1995) observed dominance of Oithona

and Acartia in a shallow, seasonally closed estuary in temperate Australia.

However, Pattanaik and Sarma (1997) documented the presence of calanoid and

cyclopoid copepods throughout the sampling period. Whereas the herpecticoids

were present during October and December in Chilka lake.

5.7.1.8. Copepod larvae In the present investigation, copepod larvae comprised of various nauplius

stages and copepodite stages and their numbers ranged from 552 to 44335 No/m3

(Table 30). The presence of fairly good number of larvae during pre- and post-

monsoon suggests that the copepods in this area breed in both the seasons.

However, seasonal distribution of this larvae revealed greater abundance in March

(Haladi-Chakra estuary) and February (confluence). A gradual decreasing trend

was observed in the monsoon season and increasing trend was noticed in

September month formed the secondary peak. In post-monsoon season, the greater

abundance was noticed in January form the third peak. Therefore from the Figure

44, it is evident that this larvae exhibit trimodal seasonal oscillation. The seasonal

variation in population density of this larvae exhibited pre-monsoon and post-

monsoon season dominant the monsoon season. The peak density of adult

copepods during pre and post-monsoon seasons almost coincides with abundance

of copepod larvae, a similar type of observation was made by Vijay Kumar (2002)

in Nethravati-Gurupur estuary and Vikas (2004) in Sita-Swarna estuary.

High abundance of copepod larvae during pre-monsoon season in the

coastal waters of Mangalore was observed by Menon et al. (1977), Benakappa et

al. (1979) and Ramesha (1989). In Nethravati-Gurupur estuary greater numbers

of these larvae during pre-monsoon season was observed by Bhat (1979),

Nagarajaiah (1980), Patil (1987) and Puranik (1990). While comparing the

seasonal variation of larvae with that of salinity, it becomes clear that copepods

exhibit intense breeding in specific salinity region such as mixoeuhaline during

pre-monsoon season and moderate breeding in polyhauline condition prevailed

during post-monsoon season.

5.7.1.9. Luciferidae

Luciferidae is chiefly represented by Lucifer hanseni, a common sergisted

occurring in the estuarine system of both the coast of India. According to Omare

(1977), this group forms a major component of the diet of fishes and shrimps.

Thus, it plays an important role in the food web of estuaries and coastal waters.

In the present study, the number of adult lucifers dominant the lucifer

larvae. These decapods were present sporadically with small numbers varying

from 01 to 61 No/m3 (Table 31). The seasonal distribution revealed the presence

of higher numbers in May of pre-monsoon season and were completely absent in

April month. In monsoon season, they were dominant in September month, but

they were not found in June and July. In Post-monsoon season, they were occur

only in two instances in October (station1 and 4). They were completely absent in

remaining months. From the Figure 45 and 46, it is clear that pre-monsoon

abundance was more dominant than the post-monsoon season. Further, it is

revealed that the more number of lucifers were present at stations situated away

from the confluence.

Menon et al. (1977), Goswami and Selva kumar (1977), Suresh and Reddy

(1975), Benakappa et al. (1979) and Patil (1987) observed a bimodal seasonal

oscillation in nearshore waters of Goa and Dakshina Kannada. Padmavathi and

Goswami (1996) documented maximum number of lucifer in April in Mandovi-

Zuari estuary. Pattanaik and Sarma (1997) recorded a greater number of lucifers in

April in Chilka lake. The present observation of greater numbers of lucifers in

May is in agreement with the works of above authors. However, Patil (1987) and

Puranik (1990) observed greater number of lucifers during October/ November

and the authors have opined that the greater number during this season was due to

the presence of higher numbers of these larval forms. Vijay Kumar (2002)

observed low density of lucifers in Nethravati-Gurupur estuary. In the present

study, lucifers with high numbers during pre-monsoon and very low to negligible

numbers during post-monsoon is found to be in agreement with the investigation

made by Vijay Kumar (2002) in Nethravati-Gurupur estuary. Very few numbers

of lucifer larvae were observed in March/April and were totally absent during

remaining part of the year. Vikas (2004) observed the greater numbers of lucifers

in April and May and were totally absent in July/August. Very few numbers were

recorded in November /January in Sita-Swarna estuary.

5.7.1.10. Decapod larvae Decapod forms an important fishery along both the coast of India. As a

result, a great deal of information is available on the occurrence, distribution and

biology of various decapods. However, the seasonal and spatial distribution of

decapod larvae as separate group among the total zooplankton community is

found to be scanty. In the present investigation, different types of decapod larvae

such as shrimp nauplii, protozoea, post larvae of shrimp, zoea, mysis, megalopa

and elima have been observed and documented in Table 32. Among the 7 larval

groups observed 4 groups such as post larvae of shrimp, protozoea, zoea, and

mysis and have been depicted graphically in Figure 47 to 50. Large number of

decapod larvae were observed by Silas and Pillai (1975), Kuttyamma (1975), Nair

et al. (1984) in Cochin backwaters. Menon et al. (1977), Bhat (1979),

Nagarajaiah (1980), Reddy (1982), Kumar (1984), Patil (1987), Puranik (1990),

Ronald (2001) and Vijay Kumar (2002) documented the occurrence and

distribution of decapod larvae in the nearshore waters in Nethravati-Gurupur

estuary, Dakshina Kannada and Vikas (2004) in Sita-Swarna estuary respectively.

Occurrence and distribution of penaeid larvae in estuarine waters of Goa

was reported by Goswami and George (1978), Achuthankutty (1987), Goswami

and Goswami (1992). In the same environment, Padmavati and Goswami (1996)

observed higher abundance of decapod larvae next to copepods. In the estuaries

along east coast of India, Gajbhiye (1981), James (1987), Pattanaik and Sarma

(1997) and Misra and Panigrahy (1999) documented higher numbers of decapods.

In the present study, shrimp nauplii varied from 01 to 02 No/m3 (Table

32). They were completely absent in station 1 (confluence region). They were

occurring in meager numbers in May/July in station 2. Lesser number of shrimp

nauplii were observed during March/ September in station 3. At station 4, they

were occurred in February/March and May. At station 5, it is occur in one

instances in May month and absent in remaining months at all stations. However,

Vijay Kumar (2002) observed abundance of shrimp nauplii in the high tide phase

during March in Nethravati-Gurupur estuary. Goswami and Goswami (1992)

observed lesser number of shrimp nauplii in the Mandovi-Zuari estuary. Ronald

(2001) recorded moderate number of shrimp nauplii during pre-monsoon season at

the confluence region of Nethravati-Gurupur estuary. Vikas (2004) recorded lesser

number of shimp nauplii during pre-monsoon and post-monsoon season in some

stations in Sita-Swarna estuary.

The post larvae of shrimp were present at all station and the number varied

from 01 to 10 No/m3 (Table 32). The seasonal distribution revealed presence of

higher number in February (station 3) and October/ November (station 2). The

larvae were observed during monsoon season at all the months at confluence

(station 1). They were occur in lower numbers in other stations. A small post-

monsoon peak was observed at October/November. From the Figure 47, it is

evident that the larvae were dominant in post-monsoon season. The spatial

variation revealed stations at confluence and Haladi estuary exhibit more numbers

than that of Chakra estuary. The pre-monsoon abundance coincided with

mixoeuhaline condition and the post-monsoon occurance coincided with

polyhauline condition. Between the two brackish water conditions, this larvae

preferred mixoeuhaline condition than that of polyhaline condition. Similar

observations were made by Goswami and Goswami (1992) in Mandovi-Zuari

estuary, Ronald (2001) and Vijay Kumar (2002) in Nethravati-Gurupur estuary

and Vikas (2004) in Sita-Swarna estuary respectively.

Protozoea stages were mainly belonging to lucifers and shrimps. The

seasonal distribution revealed the presence of this larvae in February and

September at all the stations (Figure: 48). The numbers of larvae varied between

01 to 801 No/m3. During the other stations they were totally absent in the

April/June and July month in this environment. In the Nethravati-Gurupur estuary,

Patil (1987) and Vijay Kumar (2002) recorded trimodal seasonal oscillation with

two peaks in pre-monsoon and one peak in post-monsoon season. However,

Puranik (1990) observed the presence of protozoea in March/April at station

located in the confluence of Nethravati-Gurupur estuary. Vikas (2004) observed

the protozoea in March/April at Sita-Swarna estuary, Udupi.

In the present study, zoea varied from 01 to 1640 No/m3 (Table 32). They

were present in all the months accept June/July and January at station 1

(confluence region). They were dominant in October month at station 2 in Haladi

estuary, it was not found in June/July of monsoon season. The abundance was

more in December month. At station 3, it was dominant in pre-monsoon and post-

monsoon season. It is only recorded in September month of monsoon season. The

maximum number was observed in May month of pre-monsoon season. At

station 4, in Chakra estuary they were not found in March/April and August

month. The numbers were more in September month of monsoon season. At

station 5, it was not found in April of pre-monsoon season and June/July and

August of monsoon season, but they were present in remaining months. From the

Figure 49, it becomes clear that the zoea larvae were abundant during post-

monsoon season to that of pre-monsoon and monsoon season. The spatial

distribution revealed the maximum density was occurred in Haladi estuary and

confluence region. The lower density was observed in Chakra estuary. Similar

seasonal trend was observed by Patil (1987), Puranik (1990), Ronald (2001) and

Vijay Kumar (2002) in Nethravati-Gurupur estuary and Vikas (2004) in Sita-

Swarna estuary respectively.

Achuthankutty (1987) documented the abundance of these larvae in

Mandovi-Zuari estuary. In the present study, zoea larvae were found to be

belonging to developmental stages of various types of crabs and shrimps. While

comparing the distribution of protozoea and zoea with the salinity variation, it is

evident that zoea preferred mixoeuhaline and polyhaline conditions, whereas

protozoea prefers only mixoeuhaline conditions.

In the present study, mysis larvae occurred sporadically with low numbers

and varied from 01 to 705 No/m3. The seasonal distribution revealed the presence

of moderate numbers in February/March in all stations of pre-monsoon season.

Whereas during monsoon season, mysis larvae were absent in July month in all

the station. The higher abundance was found in September month. In post-

monsoon season, they were occurred maximum number in November/December.

The seasonal variation of mysis larvae revealed that it was dominant in post-

monsoon season. The spatial distribution exhibit that mysis larvae were dominant

in Haladi estuary than that of confluence and Chakra estuary (Figure: 50). Few

number of mysis larvae without clear-cut seasonal variation were recorded by

Patil (1987), Ronald (2001), Vijay Kumar (2002) and Vikas (2004) in Nethravati-

Gurupur estuary and Sita-Swarna estuary respectively.

5.7.1.11. Molluscan larvae In the present investigation, molluscan larvae comprising of spats of

gastropods, bivalves and echinoderm larvae. The gastropod larvae varied from

133 to 1870 No/m3 (Table 33). The seasonal distribution of gastropod larvae

revealed greater abundance in March, September and October month, whereas

moderate to low numbers are present in February, April, July and November

(Figure: 51). The gastropod larvae exhibited dominant in all the seasons. The

spatial variation revealed that the station located at and near to the confluence

have more numbers than away from it.

The bivalve larvae consisted of spats of various clams and oysters. The

number of bivalve larvae varied from 133 to 2209 No/m3 (Table 34). The

seasonal distribution revealed greater abundance during monsoon season and

moderate numbers in March, April, May, September and October in almost all

stations. However, these larvae were not observed in February (station 2 and 5)

in pre-monsoon season and July in monsoon season (station 1). It is dominant in

September month except at station 5. In post-monsoon season, it is not found in

November (station 1) and November/ December (station 4) respectively. The

spatial variation revealed that the Haladi estuary and confluence dominant by

these larvae and moderate number in Chakra estuary (Figure: 52). It is

interesting to note that the larvae were present in monsoon season, when salinity

ranged between 0.21 and 23.56 ppt. The larvae were exhibited decreasing trend in

post-monsoon season, when salinity showed increasing trend.

The number of echinoderm larvae fluctuated between 02 to 801 No/m3

(Table 34). The spatial variation revealed the larvae were occured more in pre-

monsoon season and post-monsoon season (Figure: 53). The maximum number

was observed in May, September and January month. The echinoderm larvae

exhibit dominance in confluence region and Haladi estuary.

Achuthan Kutty et al. (1981) and Gajbhiye et al. (1981) observed

molluscan larvae during pre-monsoon and at the beginning of monsoon in Kajvi

and Narmada estuary respectively. Kumar (1984) recorded the abundance of

molluscan larvae during pre and post-monsoon season along the south west coast

of India. However, Habib and Rahaman (1987) documented the abundance of

molluscan larvae during monsoon season in Agnair estuary. Pattanaik and Sarma

(1997) observed sporadic occurrence of molluscan larvae in Rambha Bay, Chilka

lake. While good number of molluscan larvae were observed by Sujata and

Panigrahy (1999) in Bahuda estuary, Orissa.

In Nethravati-Gurupur estuary, Bhat (1979) recorded greater number of

these spats during late post-monsoon and early pre-monsoon. Similar observation

were made by Patil (1987), Puranik (1990), Ronald (2001) and Vijay Kumar

(2002) in the same estuary. The present observation by and large is in agreement

with the observation made by the above authors. Vikas (2004) recorded the

dominance of molluscan larvae in pre-monsoon season and moderate number in

post-monsoon season in Sita-Swarna estuary, Udupi.

5.7.1.12. Planktonic protochordates

In the present study, Oikopleura sp., doliolids and salpids were the sole

representative of planktonic protochordates (Table 35). Doliolids were present in

January (station 1) at confluence region and in May (station 2) in Haladi estuary

and were absent throughout the study period. Similarly, salpids were observed at

all stations in May (pre-monsoon) and lesser number in February/ December and

January (station 1) at confluence region. They were absent in most of the stations

during all the months in study period.

In the present study, Oikopleura sp. varied from 02 to 6681 No/m3 (Table

35). The abundance of Oikopleura sp. during pre-monsoon season was observed

in February at all the stations. This protochordate were absent in July month

throughout the study period except in station 1. The abundance of Oikopleura sp.

during monsoon season is different in different stations. The monsoon abundance

was noted in June month at station 1 and 2, September month at station 3 and in

August month in station 4 and 5. The post-monsoon peak was observed in

December/January at all the stations except at station 5. The maximum peak was

noted in November. From the Figure 54, it could be stated that this protochordates

exhibited a bimodal seasonal oscillation with peak in pre-monsoon and post-

monsoon. Pillai et al. (1975) recorded the occurrence of Oikopleura sp. from

November to April in Vembanad lake. Reddy (1977) and Eknath (1978)

encountered high numbers of Oikopleura sp. in the inshore waters of Mangalore.

Santanam et al. (1975) noted conspicuous difference in the period of occurrence

and abundance in the sea, estuarine, backwater and mangrove areas station along

the east coast. They recorded the two distinct peaks of abundance one in March

and other in October at the estuarine stations.

Sujatha and Panigrahy (1999) observed the abundance of Oikopleura sp.

during pre and post-monsoon season in Bahuda estuary, Orissa. The bimodal

oscillation in seasonal variation was documented by Bhat (1979), Nagarajaiah

(1980), Patil (1987), Puranik (1990) and Vijay Kumar (2002) in Nethravati-

Gurupur estuary in Dakshina Kannada and Vikas (2004) in Sita-Swarna estuary

respectively.

In the present study, the seasonal variation of this group is in conformity

with works carried out by above authors. The abundance of Oikopleura sp.

coincided with salinity range between highest 34.49 and lowest 0.21 ppt. The low

salinity prevailed at August month restricted the distribution in monsoon season.

Whereas at stations having salinity range between 30.05 and 11.12 ppt were

represented good number of Oikopleura sp. coinciding with the high and low

salinity regime. Similar observation was observed by Vijay Kumar (2002) in

Nethravati-Gurupur estuary and Vikas (2004) in Sita-Swarna estuary. However,

Patil (1987) and Puranik (1990) have observed greater abundance during high

saline regime (pre-monsoon).

5.7.1.13. Fish eggs and larvae

In the present study, the fish eggs were observed at all the stations during

most of the months except July. The number of fish eggs varied from 01 to 552

No/m3 (Table 36). Whereas fish larvae varied from 01 to 2762 No/m3 (Table 37).

The seasonal distribution of fish eggs revealed greater abundance in April/

May at all the stations (Figure: 55) except at station 4 and 5. The second peak was

observed in June (station 1, 2 and 3), September (station 4 and 5) and third peak

was in October (station 1 and 2) and November (station 2, 3 and 5). Therefore, it

could be stated that a clear-cut seasonal distribution could not be recognised. The

spatial distribution revealed greater frequency of occurrence at station 1, 2 and 3

compared to 4 and 5.

The examination of the fish eggs revealed the presence of different types

of eggs belonging to Carangidae, Engraulidae, Clupeidae and Scombridae. Among

them, Engraulidae dominated in September of monsoon season and Carangidae

dominant in pre-monsoon season. Whereas Engraulidae, Scombridae and

Clupeidae observed in post-monsoon season.

The seasonal distribution of fish larvae revealed greater frequency of

occurrence and abundance during post-monsoon season compared to pre-monsoon

and monsoon season (Figure: 56). During post-monsoon season, the fish larval

population consisted of Engraulidae, Scombridae, Clupeidae and Sillaginidae.

While in pre-monsoon season, fish larval population consisted of Carangidae and

Soleidae. The spatial distribution revealed greater number at the confluence. In

the pre-monsoon season, the maximum abundance was recorded in May month in

all the stations. Whereas in monsoon season, it is June (station 2 and 5), August

(station 1 and 3) and July (station 4) respectively. The post-monsoon peak was

noticed in November except station 2 (December).

Along east coast of India, Nagarajan et al. (1979) studied the fishes of

Vellar estuary in Porto Novo. Nammalwar et al. (1991) observed two peaks of

fish larvae during pre and post-monsoon season in Adyar estuary and Koralam

backwaters. Pattanaik and Sarma (1997) while working on the zooplankton

community of Rambha Bay, Chilka lake observed peak abundance of eggs and

larvae during March to September. Mishra and Panigrahy (1999) in Bahuda

estuary observed two peaks of fish eggs and larvae during November/December

and May/June. Along the coastal waters of Mangalore, Menon et al. (1977) and

Reddy (1982) recorded a good number of fish eggs and larvae during January to

April and October to December. However, Bhat (1979), Patil (1987), Puranik

(1990), Ronald (2001) and Vijay Kumar (2002) observed fairly good number of

fish larvae during post-monsoon and early pre-monsoon in Nethravati-Gurupur

estuary. Vikas (2004) documented the greater frequency of occurrence and

abundance of fish eggs in pre-monsoon season and fish larvae in post-monsoon

season at Sita-Swarna estuary. Padmavathi and Goswami (1996) while working

on zooplankton ecology in the Mandovi-Zuari estuarine system, documented

greater abundance of larvae during pre and post-monsoon season. While

comparing the distribution of fish larvae with that of salinity variation, it becomes

very clear that the larvae were more abundant, when the salinity was higher and

minimum during monsoon, when the salinity was extremely low. However, the

larvae present during monsoon season were found to be mostly belonging to

Clupeidae.

Among the various hydrographical parameters, the salinity of water was

found to exert greater influence on occurrence, abundance and distribution of

zooplankton. The relationship between total zooplankton and salinity revealed

greater abundance in mixoeuhaline condition during pre-monsoon season and

polyhauline condition during post-monsoon season. In the monsoon season, the

lesser abundance coincided with limentic condition due to south west monsoon

season. The spatial distribution revealed a greater abundance of zooplankton at

station 2 located in Haladi estuary and station 1 located in confluence region

during both pre and post-monsoon season (Figure: 63).

5.8. Macrobenthos

The qualitative and quantitative distribution of benthic organisms both in

space and time were carried out in the estuarine limbs of Haladi-Chakra estuarine

complex.

5.8.1. Qualitative composition During the present investigation different groups of benthic organisms

were recognised and they are belonging to class: Polychaeta, Crustacea, Mollusca

and along with other group of egg cases, sand tubes, annelida tube and fish. The

numerical abundance of these varied between stations and months.

The percentage contribution of polychaetes in the study period fluctuated

between 0.56 and 50.63% to the total benthos. Whereas crustaceans varied from

0.37 to 76.50%. The molluscans were dominanted throughout the period of study

and their percentage contribution to the total benthos varied from 13.89 to

97.62%. The percentage contribution of egg cases, sand tubes, annelida tube and

fish together varied from 0.0 to 34.66% to the total benthos (Table 38 to 42;

Figure: 57 to 59).

5.8.1.1. Polychaeta

During the study the species of polychaetes belongs to 7 different families

such as Nephtydae, Nereidae, Onuphidae, Glyceridae, Arenicola, Maladanidae

and Sabellaridae have been recorded. The percentage of polychaetes to the total

benthos ranged from 0.56 to 50.63%. It is evident that at station 1 located in

confluence registered higher number of Nereidae followed by Nephtydae and

Glyceridae. The percentage contribution of polychaetes to the total benthos at

confluence region varied from 0.56 to 8.42%. Whereas in the Haladi estuary

(station 2 and 3), the polychaete population was dominated by Nereidae,

Nephtydae followed by Maladanidae, Glyceridae and Arenicola. The percentage

contribution varied from 1.88 to 50.63%. Further, Nereidae at both the stations

were present almost throughout the study period. While others were not so

common and formed the bulk of the polychaete population. In Chakra estuary, the

contribution of polychaetes to the total benthos varied from 1.22 to 53.6%. At

station 4, Nereidae, Glyceridae and Nephtydae dominated the polychaete

population followed by Maladanidae. Whereas at station 5, the Nereidae

dominated in the polychaete population followed by Glyceridae and Nephtydae

located in chakra estuary. The other polychaetes belonging to Arenicola and

Sabellaridae were sporadically present with very low density in the study period.

The seasonal distribution of Polychaetes revealed greater abundance during the

monsoon season followed by pre-monsoon and post-monsoon season.

In the backwaters and estuaries of Cochin and Vembanad lake along the

west coast of India, Kurian et al. (1975), Kurian (1977), Pillai (1977), Ansari

(1977), Saraladevi and Venugopal (1989), Sunil Kumar (1995), Kumar, (1997),

Sunil Kumar, (2002a) and Sunil Kumar (2002b) observed the dominance of

polychaetes in the benthic community. Ramachandra et al. (1984) recorded higher

number of Dendronereis arborifera and Sabellaria cementarium in the polychaete

community of Mulki estuary, west coast of India.

Ansari et al. (1986) while working on the macrobenthos of Mandovi-Zuari

estuary observed 11 species of polychaetes of which Glycera alba was dominant.

Dominance of polychaetes in silty sand substratum was documented by Bhat and

Neelakantan (1988) in Kali estuary, Uttara Kannada.

Prabhu et al. (1993) observed 66 to 100% contribution of polychaetes to

the total benthos in the nearshore sediments off Gangoli, Dakshina Kannada.

Chakraborty and Choudhury (1997) observed six families of polychaetes with

Captellidae representing higher density and diversity in Hoogly estuary, West

Bengal. Sunil Kumar (2002a) in Cochin estuarine mangrove habitat observed 8

families of polychaetes with dominance of Nereidae, Eunicidae and Captellidae.

Along the east coast of India, the dominance of polychaetes both in species

and abundance at all the stations in the Vellar estuary was reported by Chandran et

al. (1982). Among the polychaetes, Nepthys sp., Polybranchia sp., Ancistrosyllis

sp., Lumbriconereis sp., Cossura sp., Glycera sp., Laonema sp. and Heteromastus

sp. were the common. Vijayakumar et al. (1991) while investigating on benthic

fauna of Kakinada Bay and backwaters recorded the dominance of polychaetes

with an average of 44.30%. While working on ecology of benthic macrofauna in

Cuddalore-Uppanar backwaters, Murugan and Ayyakkannu (1991) observed

higher contribution of polychaetes to the total macrobenthos and they have

identified 28 different species of polychaetes in the backwater system. The study

of Jagadeesan and Ayyakkannu (1992) revealed the dominance of polychaetes

followed by Crustacea in the Coleroon estuary and inshore waters of south east

coast of India and recognised more than 20 species of polychaetes and opined that

the bottom sediment and organic carbon were favorable for higher density of

fauna. Prabha Devi (1994) while studying on benthic fauna of Coleroon estuary

observed dominance of polychaetes in the benthic population, which formed

67.02% of the total fauna. The author reported 10 different species of polychaetes

with varying number in space and time. Chakraborty and Choudhury (1997)

identified 14 species of polychaetes belonging to 6 families and observed

variation of polychaetes in time and space.

In the present investigation, the seasonal distribution of polychaetes

revealed greater abundance during monsoon season followed by pre-monsoon

season and post-monsoon season. The spatial distribution indicated increased

abundance with increased distance from the confluence. While comparing the

abundance of polychaetes with that of the sediment texture, it becomes clear that

wherever the percentage of silt has increased in those stations and months

polychaete population exhibited a greater abundance, although sediment

dominated by sand throughout the period of study. The higher polychaetes

population coincided with increased silt percentage in the sediment. However,

Pillai (1977) observed greater contribution of polychaetes in sandy substratum

during the post-monsoon season. The spatial distribution indicated increased

abundance with increased distance from the confluence.

Similar relationship was observed by Chandran et al. (1982) in Vellar

estuary. Ramachandra et al. (1984) in Mulki estuary and Prabhu et al. (1993) in

the nearshore waters of Gangoli observed the dominance of polychaetes in sandy

substratum and clayey-silt substratum respectively. Sunil Kumar (2002a) observed

the relationship between sandy-silt substratums with greater abundance of

polychaetes in Cochin estuarine mangrove habitat. Nagendra Babu (2004) while

comparing the abundance of polychaetes with that of sediment texture, it becomes

clear that wherever the percentage of silt increased in those stations and months

the polychaetes dominants in Sita-Swarna estuary. Shiva Kumar (2005) observed

the abundance of polychaetes increased with percentage of silt with clay increased

in the sediments in Mulki-Pavanji estuary. In the present study, the observed

relationship between variation of polychaete population and sediment texture is in

agreement with the works of the above authors. However, Shanthanagouda (2001)

in Nethravati-Gurupur estuary could not observe any clear relationship between

polychaetes and type of sediment.

5.8.1.2. Crustacea In the present study, few individuals of crustaceans such as crabs,

juveniles of shrimps, barnacles and amphipods formed the bulk of the crustaceans.

The percentage variation of crustaceans to the total benthos varied from 0.37 to

76.50%. The class amphipods were represented family such as Gammaridae,

Caprellidae and Orechastredae. Whereas barnacles were represented by only one

species that is Balanus balanoid. In the present study, the crabs and shrimps

occurred less frequently with low to very low numbers (Table 45 to 49). It

becomes evident that the barnacles occurs more frequently than that of crabs and

shrimps. Barnacles in the present study occurs more frequently with greater

abundance. Most of the barnacles observed during the period were found settled

on small pebbles, shells of molluscs, leaves and twigs. The abundance of

barnacles in the benthic samples were observed by Bhat (1979), Ramachandra et

al. (1984), Sahoo (1985) and Shanthanagouda (2001) in Mulki and Nethravati

estuaries and Nagendra Babu (2004) in Sita-Swarna estuary respectively.

The percentage contribution of crustaceans to the total benthos at

confluence region varied from 0.44 to 6.15%. Among the crustaceans, Balanidae

(thoracica) was found to be dominated at station 1 followed by Caprellidae and

Orechastredae. In Haladi estuary, the percentage contribution of crustaceans

varied from 5.0 to 76.5%. Among the amphipods the Gammaridae and Caprellidae

occurred more frequently with higher numbers whereas, other classes were

present in lower numbers. However, Balanidae (thoracica) were observed in dead

form during pre-monsoon, monsoon and post-monsoon season and formed the

bulk of the crustaceans. In Chakra estuary, the contribution of crustaceans to the

total benthos varied from 0.37 to 62.98%. Balanidae (thoracica) and amphipoda

were observed more frequently and formed the bulk of the crustacean community.

The seasonal distribution of crustaceans revealed greater abundance of

families like Caprellidae, Gammaridae and Orechastredae of amphipoda and

Balanidae of thoracica during the monsoon season at confluence region. In post

and pre-monsoon season, these crustaceans were found in lesser numbers. Crabs

and shrimps were absent throughout the study period.

In Haladi estuary (station 2 and 3), amphipods along with barnacles were

present. At the later half of the monsoon with concomitant increase in salinity

higher numbers of Gammaridae, Caprellidae were formed the bulk of the

crustacean during monsoon season. During the post-monsoon season, the class

crustacean was represented by Gammaridae, Caprellidae and along with higher

dominance of barnacles. During pre-monsoon season, the class Gammaridae,

Caprellidae and Orechastredae along with barnacles formed the peaks with few

numbers of shrimps.

In Chakra estuary (station 4 and 5), Balanidae of thoracica and amphipods

(Gammaride/Caprellidae) formed the bulk of crustaceans during monsoon season.

During post-monsoon season, a prominent peak found to be constituted by

Balanidae of thoracica, Caprellidae, Gammaridae and Orechastredae of

amphipods along with few numbers of Squillidae of Stomatopoda and shrimps.

During pre-monsoon season, the class crustaceans were constituted of few

numbers of portunids of decapods, shrimps and large number of barnacles. The

amphipods such as Gammaridae, Caprellidae and Orechastredae formed the bulk

of crustaceans. The seasonal variation revealed that crustacean populations were

abundant in monsoon season followed by post and pre-monsoon season.

Ansari (1977) in Cochin backwater, Ansari et al. (1994) in Marmagoa

harbour, Goa recorded fairly good numbers of Gammaridae and Caprellidae in the

benthic samples. Prabha Devi (1994) observed common amphipods such as

Grandierella sp., Gileri sp. and Corophilum sp. in Coleroon estuary.

Further, the contribution of amphipods to the total bulk of crustaceans is

more than that of the other forms. The seasonal distribution of amphipods

revealed greater abundance during monsoon season followed by post-monsoon

and pre-monsoon season. It is interesting to note that during monsoon the

abundance of amphipods were responsible for bringing down the population of

polychaetes and gastropods. This relationship is more evident at stations in

Haladi estuary (station 2 and 3).

The spatial distribution revealed greater diversity of crustaceans in Chakra

estuary than that of Haladi estuary and confluence region. Ansari et al. (1986)

recognised significant contribution of crustacean to the total bulk of macrobenthos

in Mandovi-Zuari estuary, Goa. Along the east coast of India, Prabha Devi (1994)

observed fairly good numbers of amphipods in Coleroon estuary and documented

higher population in post-monsoon and lower during summer season. Ingole

(2002) recorded moderate number of amphipods in the coastal waters of Dhabhol,

west coast of India.

However, Prabhu et al. (1993), Gopalakrishnan and Nair (1998), Mohan

Kumar (1999) and Shanthanagouda (2001) could not observe significant

contribution of crustaceans in general and amphipods in particular to the total

macrobenthos in the Gangoli, Mangalore coastal waters and Nethravati-Gurupur

estuaries respectively. Nagendra Babu (2004) recorded the greater abundance of

Gammaridae and Caprellidae belonging to the class amphipods draw a significant

contribution to crustaceans, which ranged from 0.0 to 66.25% to the total macro

benthos in the Sita-Swarna estuary, Udupi. Shiva Kumar (2005) while studying on

macrobenthos observed the crustaceans percentage of 0.0 to 75.76% with

dominance of amphipods was represented by Ampithoidae, Corophiidae,

Caperillidae, Gammaridae and Hyalidae in Mulki-Pavanje estuary, Dakshina

Kannada.

5.8.1.3. Mollusca

In the present investigation, the Phylum Mollusca was represented by class

Gastropoda, Bivalvia, and Scaphopoda. In both Haladi and Chakra estuary,

molluscs were dominant in the total macrobenthic population throughout the

period of study. The percentage variation of molluscs during the study period

varied from 13.89 to 97.62%. Ansari (1977) observed the dominance of molluscs

in the Cochin backwaters. Studies of Ramachandra et al. (1984) in Mulki estuary

revealed the greater contribution of molluscs to the bulk of macrofauna. The

dominance of molluscs in the coastal waters of Mangalore was observed by

Devassy et al. (1987) and Gopalakrishnan and Nair (1998). Nagendra Babu

(2004) recorded the 12.5 to 100% of molluscs population dominating the total

macrobenthic population through out the study period in Sita-Swarna estuary.

Shiva Kumar (2005) observed the variation of molluscs to the total macrobenthos

contributed in the range of 2.27 to 94.44% in the Mulki Pavanje estuary, Dakshina

Kannada.

During the study period, the percentage contribution of molluscs to the

total benthos varied from 43.50 to 97.62% at the confluence (station 1). Among

the Phylum Mollusca, Bivalvia was more abundant followed by Gastropoda and

Scaphopoda. The Scaphopoda was represented by Dentallium. The percentage

contribution of molluscs in the Haladi estuary (station 2 and 3) varied from 13.89

to 67.29%. The percentage of gastropods was lesser than bivalves. While

Scaphopoda was reported in the month of April/May. Among the Gastropoda;

Littorinidae was abundant followed by Telescopium to the total benthos followed

by Cerithidae. Among the bivalves the percentage contribution of Meretrix sp. and

Katalysia sp. followed by Donacidae was found to be more dominated. While in

Chakra estuary (station 4 and 5), the percentage of molluscs values ranged

between 19.6 to 92.10%. The percentage contribution of gastropods was more

than bivalves. While Scaphopoda were recorded in sporadic numbers throughout

the study period. Therefore, it becomes clear that the confluence estuary supports

higher density of molluscs than that of Chakra and the Haladi estuary.

Ramachandra et al. (1984), Gopalakrishna and Nair (1998), Mohan Kumar

(1999), Shanthanagouda (2001) could not observed clear cut spatial variation of

molluscs in the coastal waters of Mangalore and Nethravati-Gurupur estuary

respectively. However, Harkantra and Parulekar (1981) in the coastal zone of Goa,

Divakaran et al. (1981) in the inshore water of Vizhinjam, Murugan and

Ayyakkannu (1991) in Cuddalore-Uppanaru backwaters and Prabha Devi (1994)

in Coleroon estuary did not observe the dominance of molluscs.

The seasonal distribution of molluscs at the confluence region revealed the

dominance of Umbonidae, Cerithidae, Turritellidae, and Conidae followed by

Olividae of the class Gastropoda. Littorinidae and Babilonia occurred in lesser

numbers. Whereas the bulk of the Bivalvia was mainly contributed by Arcidae,

Donacidae, Katalysia sp., Meretrix sp. and Perna sp. of the family Mytilidae. In

addition, Dentalidae also contributed to the bulk of the molluscan population.

During pre-monsoon season, Conidae, Umbonidae, Turritellidae and Telescopium

were abundant followed by Olividae sp., Littorinidae sp. and Babilonia sp.

Whereas the class Bivalvia was represented by Donacidae, Arcidae and spats in

large numbers along with Katalysia sp. of the family Mytilidae, thus forming the

bulk of Bivalvia. Dentallidae were present throughout the season with higher

number in pre-monsoon. During post-monsoon season, Umbonidae, Turritellidae,

Conidae and Telescopium with Cerithidae formed the bulk of gastropods followed

by Trochidae and Olividae, Archidae, Meretrix sp. and Donacidae mainly

contributed the bivalve population. The abundance and diversity of bivalves

during monsoon season is more than that of gastropods. Whereas the higher

abundance and diversity of gastropods than that of bivalves were observed during

pre and post-monsoon season. However, Dentallidae were present in large

numbers in pre and post-monsoon season. The total population of molluscs

reported to be high in February of pre-monsoon season.

In Haladi estuary at station 2, the Littorinidae formed the bulk of

gastropod population followed by Telescopium and Cerithidae. Whereas, Meretrix

sp. constituted Bivalvia. Dentallidae were reported in lesser numbers throughout

all the season. At station 3, Littorinidae of gastropods and Meretrix sp. of bivalves

were found to be abundant. Dentillidae was recorded in April/May. The species

diversity and abundance of Bivalvia is higher than gastropods. Again the total

populations of Mollusca were more in pre-monsoon season followed by the post-

monsoon and monsoon season.

In Chakra estuary (station 4 and 5), the dominance of Littorinidae,

Cerithidae followed by Telescopium of the class Gastropoda was observed. The

bivalve population consisted of katlaysia sp. of family Mytilidae followed by

Meretrix sp. Dentillidae was observed in megere numbers throughout the study

period. In post-monsoon season, the population of gastropods dominated by

Cerithidae, Turritellidae and Littorinidae. The dominance of Katlaysia sp. and

Meritrix sp. of Mytilidae was observed in the bivalve population.

In pre-monsoon season, Littorinidae and Cerithidae formed the bulk of

gastropods. While Katalysia sp. and Meretrix sp. of Mytilidae contributed to the

bulk of bivalve population. The population of Bivalvia is more than that of

gastropods in monsoon season. Whereas during post and pre-monsoon season, the

diversity of bivalves was found to be more than that of gastropods.

The seasonal distribution of molluscs in the present study revealed the

presence of high numbers during post-monsoon season followed by pre-monsoon

season. The lower numbers during monsoon season.

The spatial distribution revealed the greater numbers or diversity of

molluscs dominated in the confluence region followed by Chakra and Haladi

estuaries. So this variation was found to be due to higher percentage of sand in

sediment at confluence region followed by Chakra and Haladi estuary. In addition,

proximity to the sea and transportation of forms in to the estuarine basin could

also be the factor responsible for high population of molluscs in confluence and

Chakra estuary.

Harkantra (1975) documented the abundance of Meritrix casta from

January to July and low numbers during peak monsoon in Kali estuary.

Ramachandra et al. (1984) documented low number of molluscs during monsoon

and high population during post and pre-monsoon season in Mulki estuary.

Devassy et al. (1987) and Gopalakrishnan and Nair (1998) and Mohan Kumar

(1999) observed the peak abundance of molluscs during post-monsoon season.

Shantanagouda (2001) could not observe clear spatial variation of molluscs in the

coastal waters of Mangalore and Nethravati-Gurupur estuary respectively.

Nagendra Babu (2004) and Shiva Kumar (2005) observed the dominance of

mollusca in post and pre-monsoon season through out the study period in Sita-

Swarna estuary and Mulki-Pavanje estuary along the west coast of India.

5.8.1.4. Others

Sand tubes, egg cases, dead annelids tubes, and fishes formed the

bulk of miscellaneous forms. The percentage contribution of this group

varied from 0.0 to 34.66%. The seasonal distribution revealed the

greater numbers or diversity of miscellaneous forms dominant in the

Chakra estuary than that of Haladi estuary and confluence region

No fish was reported at confluence throughout the study period.

Whereas, egg cases dominant in monsoon season and sand tubes

occurred frequently in sporadic numbers throughout the study period.

The percentage contribution of this group varied from 0.84 to 30.4%.

In confluence, the abundance of egg cases was found to be more than

sand tubes and dead annelids tubes.

In Haladi estuary (station 2 and 3), the contribution of egg cases, sand

tubes, fish and annelida tubes were varied from 0.52 to 28.79% found to be higher

in pre and post-monsoon season, compared to monsoon season. The egg cases and

sand tubes were dominated in this group.

In Chakra estuary (station 4 and 5), sand tubes were common during pre

and post-monsoon season and found lesser numbers in monsoon season. While

egg cases and annelida were found to be higher in monsoon season followed by

pre and post-monsoon season. Fish was reported in pre-monsoon season. The

contribution of this group varied from 0.43 to 34.66%.

The seasonal variation of miscellaneous group revealed greater abundance

in pre-monsoon, monsoon season and followed by post-monsoon season.

Neelakantan et al. (1988) observed juveniles of eels in the benthic samples

collected from Kali estuary. Frequent occurrence of egg cases and sand tubes in

the Nethravati-Gurupur estuary was observed by Shanthanagouda (2001).

However, he could not observe any fishes in the benthos of same estuary.

Nagendra Babu (2004) observed the fish belonging to Engralidae were present in

the benthos collected during monsoon season at Sita-Swarna estuary, udupi.

Shiva Kumar (2005) reported the Hydroidae, sand tubes, mud tubes and egg cases

formed the bulk of miscellaneous forms. They were dominated in pre and post-

monsoon season.

The total percentage of polychaetes and miscellaneous forms contribution

to the macrobenthos in the present study were more at station 2 in Haladi estuary

with the maximum of 29.52418% and 34.91716% respectively. The greater

percentage of total crustaceans was observed in station 3, attening maximum of

38.51061%. Whereas the total percentage of molluscans was higher in station 1 at

confluence registering 28.37877%. From the Figure 64 and 65, it is evident that

the greater percentage of total polycheates, miscellaneous forms, crustaceans and

molluscans were dominant in stations at Haladi estuary and confluence region

respectively. The percentage of total crustaceans dominant the total macrobenthos

in the present investigation.