J. mar. biol. Ass. India, 46 (1) : 10 - 20, Jan. - June, 2004

Estuarine copepod abundance and diversity in relation to environmental variables, southeast coast of India

Y.N.K. Eswari and R. Ramanibai

Department of Zoology, Biomonitoring and Management Lab, University of Madras, Guindy Campus, Chennai - 600 025. India, Email: eswariyalavarthi@y-ahoo.com

Abstract

Species composition and monthly abundance of copepods in relation to environmental vari- ables were studied in Cooum and Adyar estuaries of Chennai metropolis from April 1998 to March 1999. Copepods were the dominant group contributing to 55 - 60% df the total zoop- lankton. A total of 27 taxa of copepods were recorded. Paracalanus parvus and Stenocaris-minor were the abundant species in Adyar and Acartia major and Diaptomus similis in Cooum. Among copepods, Cyclopoida constituted 46%, followed, by Calanoida (34%) and Harpacticoida (19%) respectively. The maximum (10,500 ind/m3) and minimum (300 ind/m3) abundance were noticed in August and October 1998 at Adyar and Cooum estuaries respectively. The total abundance of copepods occurred at high salinities (>30 %o) and over a high temperature range (29OC to 30°C) at Cooum Estuary as against wide salinities (>I0 to 35 %o) and narrow tempera-

ture range (>26O C to 32" C) at Adyar Estuary.

Key words : Estuarine copepods, abundance diversity

Introduction Estuaries are dynamic environments

characterized by strong vertical and lat- eral gradients in salinity, pH, suspended particulate matter, oxygen consumption and current velocities (Nolting et al., 1999). The highly productive estuarine regions play important role as nursery grounds for many commercially important fishes, especially shrimps. The environmental characteristics of tropical estuaries un- dergo short as well as long-term varia- tions in terms of nutrients caused by tidal rhythm and monsoonal cycles (Hubertz and Cahoon, 1999). Copepods occupy a strategic position in the pelagic food web because of their sheer abundance and

diversity. Moreover, they play a major role in the energy transfer of any aquatic ecosystems. Much work has been done relating to the systematics and ecology of the copepods in estuaries of India (Pillai et al., 1973; Bhat and Gupta, 1983; Mitra and Patra, 1990; Ramaiah and Vijayalakshmi, 1997; Godhantaraman, 2001) and elsewhere (Gauhan and Potter, 1994; Wooldridge and Callahan, 2000).

Cooum and Adyar estuaries are two small urban tropical estuaries situated at central zone of Chennai City, southeast coast of India, with a complexity of envi- ronmental conditions. These two are shal- low tidal estuaries flooded during mon- soonal season, like other estuaries in tropi-

Estuarine copepod abundance and diversity 11

cal region. Because of the shallow condi- tion (average depth 1.5 m) the water tem- perature and salinity are influenced by the degree of maximum tidal inflow due to ebb and flow (Godhantaraman, 2001). Studies on copepod diversity from these estuaries are meager; there is no previous account on the species composition and abundance of copepods in relation to water quality variables. Hence; the present investigation is an attempt to understand the copepod diversity in relation to physico-chemical variables from the es- tuarine water of Chennai.

The senior author is thankful to the Council of Scientific and Industrial Re- search (CSIR), Government of India, New Delhi for financial support.

with Merck Mercury thermometer of + O.l°C accuracy and pH was measured in pH mcter (Elico) with reference to a stan- dard buffer solution. For the analysis of dissolved oxygen, water samples were fixed with manganese sulphate and alka- line iodide in 250 ml BOD bottles in the field sampling sites. The unfiltered sur- face water samples were transported to the laboratory in an ice box for further analysis of physico-chemical variables by adopting standard methods given in APHA (1992). Zooplankton samples were collected by filtering 100 1 of surface water in conical plankton net with 64 pm mesh

Material and methods

Cooum (13"10f N and 80'16' E) and Adyar (13O01' N and 80°17' E) estuaries are bar built estuaries with little freshwa- ter drainage. These two estuaries are lo- cated in the central zone of Chennai City by the confluence of river Cooum and Adyar with the Bay of Bengal (Fig. l).Samples for the study were collected during April 1998 to March 1999. For the analysis of water quality characteris- tics, two stations were fixed in both the estuaries. Station 1 was selected at Cooum Estuary approximately 1 km away from the shore at a depth of about 1 m. Station 2 was in Adayar, approximately 1 km away from the shore at a depth of 1.5 m. Surface water samples were collected in one liter pre-cleaned polypropylene con- tainers. Temperature was measured in siiu Fig. 1 Location map of the study area

12 Y. N. K. Eswari and R. Ramanibai

size. Approximately 100 ml concentrate tuation was noticed in the dissolved oxy- was preserved in 5% formalin. The enu- gen concentration at both stations. The meration and counting was done by us- mean dissolved oxygen concentration at ing inverted microscope (NIKON) with station 1 (from 0 to 12.1 mg/l; mean value 100 X magnification. For each sample, 2.1 + 3.4 mg/l) was lower than at station plankton counting was made five times 2 (from 0 to 8.8 mg/l; mean value 2.2 + and the mean value was taken and ex- 2.7 mg/l). Maximum value (12.1 mg/l) pressed as number of individuals per m3. was recorded during northeast monsoon Sedgewick Rafter counting cell was used period at station 1. Hardness at station 1 for counting and standard keys ranged from 482 to 6460 mg/l and at (Kasturirangan, 1963; Rangareddy and station 2 it was 2930 to 5400 mg/l. Radhakrtishan, 1984) were used for iden- Maximum hardness (6040 mg/l) was tification of copepods. The relationships recorded at station 2 'during March and between the environmental variables and minimum (482 mg/l) was at station 1 copepod species as well as abundance during August. Annual mean hardness were analyzed by simple correlation co- was more (4796 + 1120 mg/l) at station efficients (Zar, 1987). Taxonomic diversity . 2 than at station 1 (3663 + 2537 mg/l. The of copepod community was calculated average concentration of calcium was 49.8 with the Shannon-Weaver Index (HI) 20.2 mg/l at station 1 and 39.6 + 25.5 (Shannon-Weaver, 1949). mg/l at station 2. Maximum concentra-

Results tion of chloride (70540 mg/l) was recorded in October at station 2 and minimum

En vimnmental variables (1079 mg/l) i n December at station 1.

The monthly variations of physico- Chloride showed a significant positive chemical parameters in the estuarine correlation with salinity (p < 0.001) and waters of Chennai are given in Figure 2. sulphate (p < 0.01) at station 1. The av-

The surface water temperature 26°C was erage salinity value was 22.3 * 11.3 %o

lowest in September and highest 32°C in and 27.9 + 6.8 %o at station 1 and station August and March at station 1 (Coourn 2 respectively. The lowest (3.9 %o) was

Estuary) and 26.s0C in September to 31°C recorded during northeast monsoon (De-

in April at station 2 in Adyar Estuary. The cember) at station 1. In contrast, salinity

annual mean water temperature was 28.8 was n-mximum (35.9 %o) in Marchl when

+ 2.1°C and 27.9 + 5.90C at station 1 and the rainfall was least. Sulphate ranged

station 2 respectively. PH was mostly al- from 6.2 to 26.8 mg/l at station 1 and 5.5

kaline and the minimum value was re- to 27.1 mg/l at station 2 respectively. An-

corded during November at station 1. nual mean of sulphate concentration was Annual mean pH value was recorded at 16.2 + 6.7 mg/l and 18.3 + 5.5 at station

station 1 and 2, the values being 7.6 + 0.3 1 and station 2 respectively. Phosphate and 7.7 0.3 respectively. Marked flue- concentration varied from 0.002 mg/l

Estuarine copepod abundance and diversity 13

20 =L A p M y Jun Jul A w S.p Ocl N a D r Jan F.b Mar

Ip t h y Jun Jul A w S q M N a 0- Jmn Feb Uu

" 1

I p r M y Jun Jul l u g 6.p .pal Nov Dee Jan Feb M r

. . . . . . . . . . . . 0 4

Ipr M y Jun Jul Aup SqI Ocr Nov D.0 Jm Fsb M r

I p r Way Jun Jul #ug S q .pl Nov Dec Jan F.b MI

1w4 . . . . . . . . . . . . 0 4 . . . . . . . . . . . * Ip M y Jun Jul Aug 8.p Oa Nor 0.c Jmn F.b M u Ipr M y Jun Jul l ug SqI Oct Nov h c Jan Feb M r

+ Cooum Estuary -m- Adyar Estuary I

Ip M y Jun Jul Aug 8.p 0( N a 0.c Jan F.b Mw

Month* (1998.1999)

(June) to 2.5 mg/l (February) at station 1 and 0.04 mg/l (De- cember) to 0.68 mg/ 1 (October) at station 2 respectively. The annual mean phos- phate in station 2 (0.9 + 0.7 mg/l) was higher compared to station 1 (0.3 rt 0.3 mg/l) (Table 1). Ma- jor peaks coincided with a decrease of sa- linity and an increase in the rainfall. Sig- nificant negative cor- relation was found with salinity (p < 0.05) at station 1 and station 2 (p < 0.01).

Species composition and abundance of copepods

The copepods dominated forming 55 to 60% of the zooplankton. A total of 27 taxa were re- corded during the present study (Table 2). Cyclopoids were the most diverse group accounting for 46 %, followed by calanoids (34 %) and

Fig. 2 Monthly variation of physico-chemical variables in estuarine waters of ha~acticoids (I9 %)- Chennai The maximum num-

14 Y. N. K. Eswari and R. Ramanibai

Table 1. Annual mean (, S.D.) of the physical and chemical parameters examined at the Cooum Es tuay (station 1 ) and Adyar E s f u a y (station 2) during April 1998 to March 1999

Parameters Cooum Adyar Estuary Estuary

Temperature ("C) 28.8 + 2.1 27.9 r 5.9

pH 7.6 + 0.3 7.7 + 0.3

Dissolved oxygen (mg/l) 2.1 +- 3.4 2.2 + 2.7

Hardness (mg/l) 3663 +- 2537 4796 + 1120

Calcium (mg/l) 49.8 20.2 39.6 , 25.5

Chloride (mg/l) 15750 , 12141 23985 , 22414

Salinity (ppt) 22.3 + 11.3 27.9 + 6.8

Sulphate (mg/l) 16.2 , 6.7 18.3 5 5.5

Phosphate (mg/l) 0.9 , 0.7 0.3 & 0.3

Copepod abundance ( ~ o . / m ~ ) 1613 , 139 4838 +. 250

ber of species recorded was in May at station 1, whereas it was in November at station 2. Among calanoida Acartia major, Acrocalanus gracilis, D. similis and P. aurivilli were dominant at both sta- tions. Whereas Diaptomus dorsalis and Pseudodiaptomus kiefer occurred occasion- ally at station 1 and Calanus sp., Paracalanus parvus and Rhincalanus sp. at station 2. Most cyclopoid species occurred occasionally during the study period. Mesocyclops meridianus, M. leuckarfi, Tropocyclops parcinus, Metacyclops subequlis and Paracyclops pilosus occurred once only at station 2. Few harpacticoid species such as Bryocamptus hiemalis, Microcetella rosea, Parasteneocaris sp. and Stenocaris minor were found commonly and abundantly over the entire ,period of study at station 1 and 2.

Most copepod taxa showed a distinct

seasonal pattern. D. dorsalis, P. kiefer (calanoida) M. leuckarti, M. meridianus, M. subequalis, P.vagus, T. parcinus (cyclopoida), B. hiemalis, M. rosea and S. minor (harpacticoida) were found during summer at station 1. Typical species in the postmonsoon include A. gracilis, Halycyclops spinifer and P. aurivilli. They were found in summer and southwest monsoon period. D. similis and A, major were found in all the four seasons. Over- all, the speiies number is less and un- evenly distributed. Whereas at station 2, D. similis, P. parvus and S. minor were found commonly and abundantly over the entire period of study. Typical species of southwest monsoon include M. meridionus and M. subequalis, P. vagus and Paracyclops longifurca. Cyclops scutifer, M. meridianus and Stenocaris sp. were found during summer and southwest monsoon period and H. spinifer and B. hiemalis occurred during summer, southwest and northeast monsoon. In general, the spe- cies composition and abundance de- creased from summer to monsoon.

Monthly variation of total copepod abundance is given in Figure 3. The re- sults showed that the abundance of cope- pods was higher in Adyar Estuary (sta- tion 2) with an annual mean value of 4839/m3 than in Cooum Estuary (station 1) (annual mean value 1613/m3) (Table 2). Seasonally, the abundance was the highest at station 1 during summer (mean 3800/m3) followed by southwest monsoon (1300/m3), post-monsoon (900/m3) and northeast monsoon (450/m3) respectively. Whereas at station 2, the highest seasonal

Estuarine copepod abundance and diversity 15

12000 longifurca, P. vagus, B. hiemalis,

lodo0 Parastenocaris sp., S. minor and Sfenocaris

P sp., were particularly abundant with 5 8000 c - - >1000/m3. The diversity of copepod w g 6000 community was much lower in Cooum I n C Estuary (mean annual value 0.697) than $ 4 0 0 0

in Adyar Estuary The Shannon-Weaver 2000 Index (HI) values varied from nil to 2.342

o at Cooum Estuary and nil to 2.284 in the 35000 I other estuary (Table 3). 3 m

Occun-ence of copepod in relation to environ- 25000 I . .

mental variables 5 20000 coppod abundan

0 c ,m 15000

In order to define the effects of tem- c 3 perature and/or salinity on the numerical 9 ~ o o ~ ~

abundance of total copepod, the abun- 5000 - dance data were plotted on temperature

0 Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar

- chart based On One-year

Months (19981999)

Fig. 3 Relative abundance of copepods with respect to total zooplankton counts in estuarine waters of Chennai

abundance was noticed during southwest monsoon (mean 6450/m3) followed by summer (3188/m3), post-monsoon (1250/ m3) and northeast monsoon (450/m3). Dis- tribution pattern of 7 species of copepods which are common in plankton catches of the Cooum and Adyar estuaries are de- picted in Figure 4. Population abundance of each of these species showed well marked seasonal variations. A total of 19 taxa of copepod were identified from Cooum Estuary, of which D. dorsalis, P. aurivilli, Microcyclops diversus, B. hiemalis, Parastenocaris sp., occurred at densities > 750/m3. Where as at station 2, P. parvus, Rhincalanus sp., A. major, M. fredecirnus, M. diversus, Oifhona brevicornis, P.

data sets (Fig.5). Copepods occurred in a wide range of salinity (3.9 to 35.7 %o)

combinations. But temperature has not shown wide fluctuations (26°C to 32°C). At station 1, the total abundance of cope- pods occurred at relatively high salinities (>30 %o) and over a high temperature range (29°C to 30°C). Whereas at station 2, the total copepod abundance occurred at a wide range of salinities (>I0 to 35 %o)

and a narrow temperature range (>26"C to 32°C). But in both the stations tempera- ture has not affected the species abun- dance. In tropical region the role of tem- perature is of limited significance owing to low range of variations. Although the occurrence of copepods was scattered widely in the temperature - salinity chart, their high density (10500/m3) was re- corded in high temperature (>30°C) and salinity (>25 %o) ranges.

16 Y. N. K. Eswari and R. Ramanibai'

Acrocalanus gracilis

, . . . . . . . . . . . . . , .

- - - - - - -

1000 1600 -

Pseudodiaptomus aurivilli

MM-

3500 - 2000 - Stenocaris minor Bryocramptus hiernalis

3000 - ? ... , .

2500 - . * . . . . . . . . . . 2000 - . . . . . . , . . ' . . . . . . ;' *., 1500 - : : . . . . t : 1000 - : : : :

. . I . . . . . . , . . .

, . . ,

. . , , . . 1200 - 0.' \ . . . . 1000 -

800 -

Diaptomus sirnilis : : : , .

1400,-

Apr May Jun Jut Aug Sep Ocl Nov Dec Jan Feb Mar Apr May Jun Jut Aug Sep Oct Nov Dec Jan Feb Mar

Acartia major

.:?

Apr May Jun Jul AUQ Sep Oct Nov Dec Jan Feb Mar

Months (19951999)

[d station 1 ---..- station2J

loo0 ~

Fig. 4 Distribution pattern of common copepods in the Cooum and Adyar estuaries during Apr. 1998 - Mar. 1999

900 - 800 - 700 -

Microsetella rosea

. . , . . , . . . , . . ; : : : . < . . . . . . . . . . . . . , ..: . . . . . ,

, . , . : s

, . #' '.. . . . . . . . . . , . . . , . , . . ;:

Estuarine copepod abundance and diversity 17

Table 2. Species list of copepods and maximum abun- dance (No./m3) recorded at Cooum and Adyar estuar- ies.

Group Cooum Adyar Estuary Estuary

Calanoida Acartia major

Acrocalanus gracilis

Calanus sp.

Diaptomus dorsalis

D. similis

Paracalanus parvus

Phyllodiaptomus kiefer

Pseudodiaptomus aurivilli Rhincalanus sp. Cyclopoida Cyclops scutifer Halicyclops spinifer

Mesocyclops leuckarti

M. meridianus

Metacyclops subequalis

M. tredecimus

Microcyclops diversus

Oithona brmicornis

Paracyclops pilosus

P. longifurca

P. vagus

Tropocyclops parcinus

Harpacticoida

B yocamptus hiemalis

Microsetella rosea

Parastenocaris sp.

Stenocaris minor

Stenocaris sp.

Discussion

Cooum and Adyar estuarine system undergo important hydrobiological changes during monsoon months, similar to other estuaries. During the monsoon the Adyar Estuary remains marine in

E .- E - .- - d 0

o 8 0 Temperature

1

Station 2

Temperature

Fig.5 Abundance - temperature - salinity diagram for copepods

Table 3. Monthly variation of the Shannon-Weaver Index (H') of the copepod abundance at Cooum and Adyar estuaries. - -

Month Cooum Adayar

(1 998-99) Estuary Estuary

Apr. 1.395 1.544

May 2.342 1.556

Jun. 1.332 1.627

Jul. 1.544 1.638

Aug. 0 2.143

S P . 0 0 Oct. 0 1.257

Nov. 0 2.289

Dec. 0 1.322

Jan. 0.693 1.098

Feb. 0 1.448

Mar. 1.06 1.011

18 Y. N. K. Eswari and R. Ramanibai

nature, the other estuary becomes almost freshwater due to drainage from its catch- ment area resulting in wide salinity varia- tion (3.89 to 35.68 %o). This fluctuation in salinity influences the taxon composition in the area. The hydrological features varied remarkably across the seasons. The highest temperature was recorded in May under summer season. The lowest pH was recorded during northeast monsoon (No- vember), assuming a direct effect of rain- fall and considering rapid intrusion of freshwater runoff. Dissolved oxygen was present only during summer, monsoon

sheltered systems like estuaries (Goswami, 1982). In the Cooum and Adyar estuarine waters, the total abundance of copepods were highest in summer and southwest monsoon (premonsoon) than the other seasons, as commonly observed in many marine coastal and estuarine waters (Madhupratap, 1979; Goswami, 1982; Padmavati and Goswami, 1996). High proliferation of copepods in summer months might be attributed to high tem- perature and' phytoplankton abundance, which often is considered as the most im- portant factor favourable for copepods.

and postmonsoon seasons at station 1 and The abundance of copepods was low- station 2. It was completely absent during est during monsoon months, when the Premonsoon. The low Oxygen ' water column was markedly stratified to

might be due to the inflow of water a large extent because of high rainfall. As containing sewage and waste a result of these, water temperature, sa- from urban areas and may be an indica- linity and phytoplankton abundance de- tor of the occurrence of eutrophication creased largely with increased turbidity. and degradation of organic matter. This has been observed in many Indian

Salinity was greatly reduced during the monsoon season and attaining maximum during summer season. Phosphate distri- bution in the estuary remained salinity influenced. Significant negative correla- tion was found between salinity and phosphate at station 1 (p < 0.05) and at station 2 (p < 0.01). The presence of phosphate in an estuary can be taken as an index of potential fertility of the eco- system as a whole. In general and in particular in tropical waters, the chang- ing nature of the environmental variables would effect the occurrence, composition and distribution of plankton and the variations are well pronounced in the

estuaries (~hetty'et al., 1982; Dutta et al., 1990). Moreover, many copepod species disappear during monsoon and species composition also changed, since they are mostly stenohaline. When the conditions are favourable, normal plankton compo- sition reappeared. Further, the species composition is positively correlated with pH (p < 0.05), hardness (p < 0.01), chlo- ride (p < 0.01), salinity (p < 0.01) and sulphate (p < 0.01), showing that the com- munity as a whole preferred high saline conditions. Although higher copepod abundance was observed at high oxygen concentrations, substantial concentrations were recorded at < 1.0 mg/l. This

Estuarine copepod abundance and diversity 19

indicated that deoxygenation did not cause serious problems for copepod abun- dance (Godhantaraman and Uye, 2003).

Marked seasonal fluctuations have also been noticed with respect to the number of species present in the plankton popu- lation. A maximum of 12 species of cope- pods were encountered in the plankton at station 2 in November and the lowest number of species (1) was at station 1 during August to October. The dominant copepods were A. major, A. gracilis, D. similis and P. aurivilli. The abundance of these species might be due to their con- tinuous breeding nature and the sustain- able environmental conditions of the eco- - system. Similar dominance of these spe- cies was reported in the Mandovi-Zuari estuaries (Dwivedi et al., 1974).

Although hydrobiological parameters do exert some influence, they have, as yet, not shown in statistically significant effect on the copepod abundance. However, it is a difficult task to evaluate the factors responsible for the variation of copepods in any environment which are subjected or not to periodic changes. In view of the fact that changes in population structure are defined not only by the dynamics of processes internal to environments, but also by the addition and superposition of changes in the surrounding environments of the estuaries.

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