Freshwater diatom diversity in Deepor Beel - A Ramsar site

Freshwater diatom diversity in Deepor Beel - A Ramsar site

Keywords: Freshwater diatoms, diversity, Frustule, Deepor Beel, Ramsar site

182-191 | JRPS | 2013 | Vol 2 | No 2

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Authors:

Lisha Gurung1, Alak

Kumar Buragohain2,

Sailendra Prasad Borah1

and Bhaben Tanti1*.

Institution:

1. Department of Botany,

Gauhati University,

Guwahati-781014, Assam,

India.

2. Department of Molecular

Biology and Biotechnology,

Tezpur University, Tezpur-

784028, Assam, India

Corresponding author:

Bhaben Tanti.

Email:

[email protected]

Web Address: http://www.plantsciences.info documents/PS0055.pdf.

Dates: Received: 12 Mar 2013 Accepted: 20 Mar 2013 Published: 29 May 2013

Article Citation: Lisha Gurung, Alak Kumar Buragohain, Sailendra Prasad Borah and Bhaben Tanti. Freshwater diatom diversity in Deepor Beel - A Ramsar site. Journal of Research in Plant Sciences (2013) 2(2): 182-191

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ABSTRACT: This study was conducted for an investigation of freshwater diatom diversity in Deepor beel, a Ramsar site of Assam, India. The water samples were collected from six different sites on the basis of habitat stratification. The study was carried out from April 2010 to March 2011. Laboratory pure cultures in diatom specific media followed by microscopic investigations supplemented with taxonomic keys, aided in identification of the diatoms were undertaken. The results showed that there were 65 species of diatoms, belonging to 26 genera of which 53 were pinnate and 12 were centric types. The dominant species were found to be Nitzschia, Pinnularia and Navicula respectively. Abundance of diatom species provides evidence for their important role as primary producers in this wetland ecosystem of Deepor beel of Assam.

INTRODUCTION

Diatoms are unicellular, eukaryotic, microscopic

algae belonging to the class Bacillariophyta. They are

photosynthetic and usually appear golden-brown in

color, abundant in both freshwater as well as marine

environment (Beakes et al., 1988). The characteristic

feature of the diatom is its cell wall known as frustules,

which is heavily impregnated with amorphous silica. The

structure and arrangement of the diatom frustules could

be used as a taxonomic criterion for identification up to

their species level. They are the only organisms known to

process genetic ability to mineralize amorphous silica

into complex structures. Diatoms have recently evolved

tremendous interest for their silica nanostructures, which

have unending possibilities in the field of engineering,

electronics and medical science (Pareek et al., 2011;

Koen et al., 2003; Taylor et al., 2005).

Diatoms play very important ecological roles.

They play a key role in the global carbon cycle, fixing

25% of the carbon each year (Jones, 2007). Therefore,

this group of organism contributes a major amount in the

primary productivity of our ecosystem. Diatoms also

involve in the silica cycling pathways on the earth.

Benthic diatoms are very diverse and can live

either free floating as phytoplanktons or in the sediments,

or attached to the rocks (epilithon), sand grains

(epipsammon), and aquatic plants (epiphyton). Diatoms

living on soft sediments (epipelon) are often motile

species that are able to migrate up and down in the

sediment matrix. Attached communities can be closely

attached to the substrate; e.g., Cocconeis or attached by

mucilaginous stalks e.g., Gomphonema. Often diatoms

can group themselves into 3-dimensional communities

forming complex microscopic forests. Diatoms can also

form part of the diverse 3-dimensional microbial

communities of filamentous algal mats which form in

streams and lakes, in some cases forming perennial

layers up to 30 cm thick (Rai, 2006).

Deepor Beel, located in the vicinity of Greater

Guwahati, Assam (Latitude 26°7'26'', longitude

26°38'49'') is an important wetland of North East India.

This wetland has enormous ecological and economic

significance (Gogoi 2007). Considering the necessity of

protection and conservation, Deepor Beel has been

included amongst the few Ramsar sites. The diatom

species are known to play critical roles in wetland

ecosystems. The diatom diversity has not been assessed

at this important Ramsar site of Assam, India.

Therefore, the present study was emphasised to explore

the diatom diversity at Deepor Beel.

MATERIALS AND METHODS

Collection of samples and culture conditions

Water and semi aquatic soil samples were

collected from six different sites of Deepor Beel

ecosystem on the basis of habitat stratification from

April 2010 to March 2011 (Figure 1). Freshly collected

samples were immediately transferred in the DM

(Diatom Medium) proposed by Beakes et al., (1988).

The medium was standardized with slight modification

and the composition was as follows: Ca(NO3)2. 4H2O -

0.02 g, KH2PO4 - 0.0124 g, MgSO4.7H2O - 0.025 g,

NaHCO3 - 0.0159 g, EDTAFeNa - 0.225 mg, EDTANa2

- 0.225 mg, H3BO3 - 0.248 mg, MnCl2.4H2O - 1.39 mg,

(NH4)6Mo7O24.4H2O - 1.0 mg, Cyanocobalamin -

0.04 mg, Thiamine Hcl - 0.04 mg, Biotin - 0.04 mg and

NaSiO3.9H2O - 0.114 g in 1 L distilled water, adjusted to

pH 6.8. Cultures were allowed to grow at 3K light and

18-20°C for 15-20 days. Repeated subcultures were done

on solid medium to obtain pure cultures of diatom

species.

Diatom cleaning for microscopic analysis

Diatoms obtained in pure cultures were cleaned

for microscopic analysis following the protocol of

Battarbee et al., (2001) with slight modification. Equal

volume of 10% HCl solution was added to the diatom

cultures. After proper mixing, 6 ml of a 30% H2O2

Gurung et al.,2013

183 Journal of Research in Plant Sciences (2013) 2(2): 182-191

solution was added, heated in a water bath at 40°C for 20

min and then cooled. A drop of NH3 was added and

centrifuged for 5 min at 4000 rpm in a 20°C centrifuge

and decanted the supernatant. Cleaned diatom samples

were used to prepare permanent slides with Naphrax

(mounting medium with refractive index 1.73.

The slides were analyzed under a Light

microscope and examined for the presence of specific

genera of diatoms (Nikon, Eclipse-E200, with photo

micrographic attachment).

Identification

Taxonomic identifications and nomenclatures

were made by consulting various literatures and

monographs (Gandhi, 1955; Husted, 1959; Hendey,

1964; Patrick and Reimer, 1966; Prescott, 1975;

Desikachary, 1989; Round et al., 1990; Nautiyal et al.,

1996 and Anand, 1998). In this study, the diatoms

obtained in pure culture were identified up to genus level

only.

RESULTS AND DISCUSSION

A total of 65 species of freshwater diatoms were

recorded in the Deepor beel of Assam, India. Pure

cultures of diatoms in terms of frequency and abundance

belonged to 27 genera of which 53 are pennate and 12

are centric type. The major genera were found as

Nitzschia (10), Pinnularia (9), Navicula (7), Eunotia (5),

Cyclotella (3), Stauroneis (3), Melosira (3),

Gomphonema (2), Achanthes (2), Achmanthas (3),

Mastogloia (2), Pleurosira (2). The single species of

Gurung et al.,2013

Journal of Research in Plant Sciences (2013) 2(2): 182-191 184

Figure 1: Map showing six different sample collecting sites at Deepor Beel, Assam, India

following diatoms: Synedra, Rhopalodia, Cocconeis,

Cymbella, Luticola, Meridion, Denticula, Diploneis,

Eucocconeis, Placoneis, Stephanodiscus, Thalassiosira,

Coscinodiscus, Aulacoseira (Figure 2-7) were found on

the examined site. In this study, the diatoms obtained in

pure culture were identified up to their genus level,

because for species level identification correctly, detailed

study will be required for characterizing their

ultrastructure of frustules through scanning electron

microscopy. Further, no diatom culture collection facility

is available in India due to which identification up to

species level is very much difficult.

Out of 65 isolates obtained in pure cultures, 10

diatoms were found to be different species of Nitzschia,

representing 15% of the total diatom flora. Further, there

were 9 different species of Pinnularia, representing 14%,

followed by Navicula (11%), Eunotia (8%), Stauroneis

and Melosira representing 5% each, Cyclotella (4%),

and 3% each of Gomphonema, Achanthes, Achnanthes,

Mastogloia and Pleurosira respectively. The rest 14

Gurung et al.,2013


Figure 2(A-I): Pinnularia

Figure 3 (A-J): Nitzschia

diatoms were represented by only one species showing

21% out of the total diatoms obtained in pure cultures

(Figure 8).

Taxonomic descriptions of few major diatom

species found in Deepor beel during study period are as

follows:

Gurung et al.,2013


Figure 4: A – F, Navicula, G & H - Gomphonema, I & J - Achanthes, K-M, Achmanthas

Figure 5: A – E, Eunotia, F- Navicula, G – Mastogloia, H- Synedra, Rhopalodia, J- Cocconeis, K- Cymbella

Class: Bacillariophyceae

Order: Bacillariales

Sub-order: Coscinodiscineae

Family: Coscinodiscaceae

Genus: Cyclotella, Kuetz., 1834

Cyclotella sp. (Fig. 7 A-C)

Valves circular; central area smooth or rarely

finely punctuate; marginal striae coarse, wedge-shaped,

diameter 12.5 μm and Striae 9 in 10 μm.


Order: Eunotiales

Sub-order: Eunotiineae

Family: Eunotiaceae

Genus: Eunotia, Ehrenberg 1837

Eunotia sp. (Fig. 5 A-E)

Valves crescentric to arcuate, more or less

parallel sides and slightly narrower rounded apices; short

raphe at the ventral margin near the poles; polar nodules

small; striae parallel, 45-46 μm length, 3.5-5.2 μm width,

Striae 13-14 in 10 μm.



Sub-order: Naviculineae

Family: Naviculaceae

Genus: Navicula, Bory 1822, emend. Cleve 1894

Navicula sp. (Fig. 4 A-F)

Valves broadly elliptic; apices short rostrate and

broadly rounded; axial area narrow, parallel; central area

widened and irregular; raphe straight, median with

distinct central nodules; striae radiate through, striae

around the central area alternately long and short, 32 μm

length, 15 μm width, Striae 8-10 in 10 μm.


Order: Naviculales

Family: Pinnulariaceae

Genus: Pinnularia, Ehrenberg 1840

Pinnularia sp. (Fig. 2 A-I)

Valves linear or elliptic-linear with parallel or

slightly convex sides; apices slightly pointed or broadly

rounded; axial area wide, linear, large central area

somewhat elliptic and slightly wider on one side; raphe

broad and undulate with approximated central nodules

and hooked terminal fissures; striae very coarse,

punctuate, striae radiate becoming parallel convergent

towards the poles, 94 μm length, 15-16 μm width, Striae

9-10 in 10 μm.

Gurung et al.,2013


Figure 6: A – Luticola, B – D, Stauroneis, E- Meridion, F– Denticula, G- Mastogloia, H- Diploneis,

I- Eucocconeis, J- Placoneis, K- Achmanthas


Order: Cymbellales

Family: Gomphonemaceae

Genus: Gomphonema, C.A. Agardh 1824

Gomphonema sp. (Fig. 4 G & H)

Valves broad, clavate with an apiculate head pole

and a capitate foot pole; axial area linear, widening into a

round or elliptical central area, which is wider on one

side and has an isolated pore on the primary side of the

central nodule; raphe straight with hooked terminal

fissures; striae coarsely punctate, slightly radiate, striae

shorted and wider around the central area, 48.5 μm

length, 10 μm width, Str 10-12 in 10 μm.


Order: Cymbellales

Family: Cymbellaceae

Genus: Cymbella, C.A. Agardh 1830

Cymbella sp. (Fig. 5 K)

Valves asymmetric, semi-lanceolate, dorsal side

convex and ventral side almost straight and slightly

expanded at the centre of the valve; apices slightly

rostrate and broadly rounded; axial area broad and

widening into an elliptic central area; raphe located

slightly closer to the ventral valve margin, very slightly

curved; striae radiate, 130 μm length, 29 μm width,

Striae 8-10 in 10 μm.

Gurung et al.,2013


Figure 7: A – C: Cyclotella, D & E- Pleurosira, F- Stephanodiscus, G- Thalassiosira, H- Coscinodiscus,

I and K – Melosira, J- Aulacoseira


Order: Fragilariales

Family: Fragilariaceae

Genus: Synedra Ehrenberg 1832: 87

Synedra sp. (Fig. 5 H)

Valves linear to linear lanceolate and tapering at

the poles, sometimes narrow with capitate ends; ends

rounded pseudoraphe linear, central area absent, striae

coarse. Length 95 to 156 μm, breadth 7 to 9 μm, striae 9

to 11 in 10 μ.



Family: Bacillariaceae

Genus: Nitzschia, Hassall, 1845: 435

Nitzschia sp. (Fig. 3 A-J)

Frustule showed wide variation among the

species, generally narrowly linear. Some species

revealed small frustules, valves linear to linear

lanceolate, with slightly constricted, shortly wedge

shaped, acute rounded or capitates ends. Striae fine and

almost indistinct. Length 15 to 26 μm, breadth 2.5 to 4.5

μm, striae 32 to 35 in 10 μm and punctae 10 to 13 in

10 μm.


Order: Acnanthales

Family: Achnanthaceae

Genus: Achnanthes, C.A. Agardh (1824)

Achnanthes sp. (Fig. 4 K-M)

Valves – linear, lanceolate in outline, gibbous in

the middle; ends obtusely rounded. Valve with raphe

were straight with distinct central pores, axial area

narrow and linear. Central area broad reaching the side

walls. Length - 40 to 46 μm, breadth 8.5 to 10 μm.


Order: Melosirales

Family: Melosiraceae

Genus: Melosira, C.A. Agardh (1824)

Melosira sp. (Fig. 7 I-K)

Frustules cylindrical, united in chains, mantle

line straight. Surface of the Mantle punctate with

puncta in spiral rows. Diameter of the cell 7 to 12 μm.

Height of half cell 8 to 14 μm.


Order: Thalassiosirales

Family: Thalassiosiraceae

Genus: Thalassiosira, Hasle & Heimdal, 1970

Thalassiosira sp. (Fig 7G)

In valve view, the frustules is circular with a

diameter ranging from 3.8 to 6.0 μm, averaging 4.5 μm,

regular occurring bright spots, areas of greater density,

observed around the margin ca. 0.9 μm apart.


Order: Aulacoseirales

Family: Aulacoseiraceae

Genus: Aulacoseira, (Ehrenberg) Simonsen 1979

Aulacoseira sp. (Fig. 7J)

Circular valve ranging from 12 to 15 μm in

diameter and the length of the mantle from 15 to 18 μm,

the valve face covered with areolae, areolar rows are

usually spiral and in some population straight, spines

large and sharply pointed.


Order: Coscinodiscales

Family: Coscinodiscaceae

Genus: Coscinodiscus, Gran and Angst 1931

Coscinodiscus sp. (Fig. 7H)

Gurung et al.,2013


Figure 8: Diversity of diatom flora in Deepor beel.

Cylindrical, pervalvar axis varying from about ½

to the whole length of the diameter. The transition from

valve face to valve mantle abrupt, forming nearly 90

degree angle, the valve centre irregular hyaline due to

variable termination of the radial rows of areolae, valve

mantle large, 30-40 μm in the pervalvar direction, with

slightly larger areolae, 4-6 in 10 μm.


Order: Thalassiosirales

Family: Stephanodiscaceae

Genus: Stephanodiscus, Ehrenberg, 1845

Stephanodiscus sp. (Fig. 7F)

Cells discoid, ring of spines were present around

the valve face, areolae simple round pores, areolae of the

valve mantle slightly closer together and often occur in

diagonal rows without intervening costae, mantle edge

often vertically grooved areolae 12-18 μm in 10 μm.

Majority of the forms were solitary and few

colonial. Distinct numbers of dominant genera of

pennate diatoms like Nitzschia, Navicula, Gomphonema,

Cymbella, Synedra etc. were dominant throughout the

year. Further, Nitzschia and Pinnularia were found to be

common in all the selected locations. Centric diatoms

like Coscinodiscus, Stephanodiscus, Melosira and

Aulacoseira were most dominant during the spring.

Taxonomic investigations on the diatom flora of

Assam are still much limited and most studies were

performed randomly along with other algae. Northeast

India in general and Assam in particular is one of the

biodiversity hotspot which along with different

demographic and geographical patterns create diverse

types of ecological niche, supporting different types of

diatoms, thereby requires a more extensive exploration

and documentation of its diatom flora. The establishment

of a diatom database would be an essential contribution

to the conservation and exploitation of its aquatic

biodiversity (Round et al. 1990).

All diatoms were solitary and only Melosira and

Aulacoseira were found in colonial form. Particularly,

diatoms like Nitzschia, Navicula, Eunotia, Cyclotella,

Melosira, Pleurosira and, Eucocconeis were most

dominant during the monsoon whereas distinct numbers

of dominant genera of diatoms like Nitzschia, Navicula,

Cyclotella, Pleurosira, Synedra and Eucocconeis were

dominant during winter season. The Nitzschia, Navicula,

Eunotia, Cyclotella, Gomphonema, Pleurosira, Synedra,

Diploneis and Eucocconeis were found to be most

abundant in all the seasons. In this study, the diatom

diversity clearly depicts highest number of diatoms in

winter, followed by that in post monsoon, summer and

least was recorded in monsoon season. This finding is in

good agreement with some previous reports (Singh et al.

2011).

CONCLUSION

In the present investigation, 65 diatom taxa under

26 genera were obtained in pure cultures from Deepor

Beel, Assam, India, which is an evident of rich diatom

taxa in this important Ramsar site of Assam. As diatoms

play very important roles from ecological point of view,

therefore, the present basic information of the diatom

database, their distribution and diversity would form a

useful tool for further ecological assessment and

monitoring of the Deepor beel.

ACKNOWLEDGEMENT

I would like to thank Dr. G.C. Sarma,

Department of Botany, Gauhati University, Assam for

helping in identification of the specimens. F i n a n c i a l

support received from the North East Center for

Research & Development (NECRD), IGNOU, Govt. of

India, grant no. IG/NECRD/09-10/RES/PROJ/

BT/52/721 is highly acknowledged.

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