J. mar. biol. Ass. , 45 (2) : 144 - 152, July - Dec., 2003

Diversity of zooplankton in coastal waters, southeast coast of India

P. Santhanam and P. Perumal.

Centre of Advanced Study in Marine Biology, Annarnalai University, Parangipettai - 608 502 , India

Abstract Results of an investigation carried out on the spatio-temporal variation of zooplankton in the Bay of Bengal (Station 1) and Vellar Estuary (Station 2) from September 1997 to August 1998 are presented. Hydrological parameters such as water temperature, salinity, pH and dissolved oxygen were noticed in the ranges of 26.5-32.OC; 3-34%0;7.05-8.63 and 3.6-8.6 ml/l respec- tively. The inorganic nutrients like nitrate, nitrite, phosphate and silicate concentrations varied between 4.2 and 49.6pM; 0.9 and 7.9pM; 0.6 and 2.l;iM and 7.9 and 139.9,uM respectively. Totally 50 species of zooplankton and 17 varieties of larval forms were identified from 2 stations. Of these, the copepods were the dominant group. The popuIation density varied from 560 to 87,780 No./m"at station 1 and 184 to 1,56,164 No./m3atstation 2. Species diversity was higher (1.89-4.01bits/individual) at station 2 than at station 1 (1.83-3.96bits/individual). Higher values of plankton density and diversity were found during summer and post mon- soon seasons and they were positively correlated with salinity and surface water temperature.

Introduction 1973; Vijayalakshmi and Venugopalan, The Vellar Estuary is situated at 1973; Sivakumar, 1982; Chandran and Parangipettai (11" 29' N; 79" 46' E), east Ramamoorthi, 1984a and b; Chandran, coast of India. It has a year round connec- 1987). Reasonable extent of information tion with the Bay of Bengal and is sub- on the seasonal distribution of zooplank- jected to semidiurnal tides with a maxi- ton from Parangipettai coastal waters are mum tidal amplitude of about 1 meter. also available (Subbaraju, 1970 The Vellar Estuary is connected with the Krishnamurthy and Santhanam, 1975; Coleroon Estuary through Backwa- Santhanam et. al., 1975 and Kumar, 1993). ter and mangrove channel. Recently many shrimp farms have been Much information is available on the established on the banks of the Vellar physico-chemical properties of the Vellar Estuary, hence an investigation on the. Estuary and the adjacent waters diversity of zooplankton of the (Krishnamurthy, 1967; Ramamoorthi, Parangipettai coastal environs was un- 1971; Krishnamurthy and Sundararaj, dertaken in relation to the hydrobiology Diversify of Zooplankton in Parangipettai coastal waters 145 of the area during September 1997 to Strickland and Parsons (1972). Surface August '98. samplings of zooplankton were made at monthly intervals by horizontal towing of The authors are thankful to the Direc- tor of CAS in Marine Biology and the plankton net (0.35 m mouth diameter) authorities of Annamalai University. made up of bolting silk (cloth No 10; mesh size 158,um) for twenty minutes. The col- Material and methods lected samples were preserved in 5% For samplings, two sites representing neutralized formalin and used for quali- the sea (Bay of Bengal-stationl) and the tative analysis. A known quantity of water estuary (Vellar-station 2) were chosen. (1000 litres) was filtered through a bag Station-1 is located 3 km away from the net of the same mesh size and the numeri- mouth of the Vellar Estuary and station- cal plankton analysis was carried out using 2 situated just opposite to the Marine a binocular microscope. Zooplankton di- Biological Station (Fig.1 ). Rainfall data versity was calculated using Shannon- were obtained from the local meteorologi- Weaver's index (Pielou, 1975)' species cal station at Parangipettai. Temperature richness was calculated by Simpson's was measured using a standard centigrade index. Species evenness was calculated thermometer. Salinity was estimated by using the formula of Pielou (1966). refractometer and pH was measured us- Results ing ELICO Grip pH meter. Dissolved Physico-chemical parameters oxygen was estimated by the modified Winkler's method (Strickland and Parsons, Monthly rainfall ranged from minimum 1972). Nutrients were analysed by adopt- value (55.2 mm) recorded during the ing the standard procedures described by premonsoon season to the maximum value (895.5 mm) recorded during the monsoon season. No rainfall was recorded during January to April and in June. Surface water temperature ranged

from 26.5 " C to 31.0 O C at station 1 and from 28°C to 32°C at station 2 (Fig.2). Salinity showed wide variations and fluc- tuated from 6 to 35 %O at station 1 and 3 to 34 %O at station 2 (Fig.3). The pH ranged between 7.1 and 8.6 at station 1 and 7.0 and 8.6 at station 2 (Fig.4) where in low values were recorded during the premonsoon season and higher values during the postmonsoon season. Dissolved Fig. 1. Map showing station positions oxygen concentration (ml/l) varied from 146 P. Santlzanam and P. Perumal

fi 10 0-r~ 8 E"0 '30 '30 - L 0 C 5 6 eJ $5 E U 4 V 5 E El aLa) 2 V, 0

Fig. 2. Variations in surface water temperature

Fig. 5. Variations in dissolved oxygen

ing the monsoon season and the mini- h I J 30- mum concentration during the summer w 20 - season at both the stations. .-Y 9 lo- In the case of nutrients, the ranges (yM) Lz o., of nitrate and nitrite were: 4.2 - 40.5 at r-c0,x 222222 station 1 and 5.6 - 49.6 at station 2; 0.9 w cj v3 h - 6.8 at station 1 and 1.5 - 7.9 at station 2 respectively. The ranges (yM) of phos- Fig. 3. Variations in salinity phate and silicate concentration were 0.6 - 1.8 in station 1 and 0.7 - 2.1 in station 3.6 to 7.8 at and 3.8 to 8.6 at 2; 7.9 - 109.0 in station 1 and 11.9 - 139.9 station (Fig.5) with the in station 2 respectively (Figs.6-9). At both

9 I 1 Station 1 Station2 I

Fig. 4. Variations in pH Fig. 6. Variations in nitrate concentration Diversity of Zooplankton in Parangipettai coastal waters

Station 1 140 E n [7 Station2 120 r g 1, 80

.m9 f3 2 40 20 0

Fig. 9. Variations in silicate concentratiorz Fig.7. Variation in nitrite concentration ifera: Globigerina rubescens; Copepoda: stations all the nutrients were low during Calanus sp., Nannocalanus minor, the summer season and high during the Xhincalanus cornutus, Eucalanus attenuatus, monsoon season. E.elongatus, Paracalanus parvus, Zooplankfon disfribufion Acrocalanus gracilis, Centropages furcat us, C.gracilis, C.orsinii, Pseudodiaptomus A total of 67 zooplankters belonging to annandalei, P.aurivilli, Temora turbinata, the following groups were encountered. T.discaudata, Labidocera acuta, L.pectinata, Ciliata: Tintinnopsis tocantinensis, Acartia erythraea A.spinicauda, A.danae, T. fubulosa, T.cylindrica, T.minuta, Favelle A.southwelli, A.clausi, Microstella rosea, philippinensis and Colenterata: F.brevis; Macrostella gracilis, , Euterpina acutifrons, Bougainvilla sp.; Ctenophora: Pleurobrachia Oithona rigida, O.similis, O,nana, sp.; Rotifera: Brachionus angularis, B.plicatilis and Monostyla bulla; Foramin-

22.5 7 Station 1 Station2

El Chaetognatha WForaminifera Decapoda Copepoda Larval form

Fig. 10. Percentage composition of zooplankton - Fig. 8. Variations in phosphate concentration station 1 148 P. Santhanam and P. Perumal

I --t station 11

d( 8 Protozoa Rot~tera Fl Chaetognatha tl Foram~n~fera W Coelenterata Ctenophora Decapoda Fi Copepoda I7 Amphipoda Larval form, Fig. 13. Monthly variations in species diversity

Fig. 11 Percentage composition of zooplankton - station 2 brachyuran zoea, shrimp mysis and crab megalopa ; and fish eggs. O.spinirostris, O.brevicornis, O.plurnifera, At station 1, forty-four groups of zoop- Oncaea venusfa and Corycaeus vitrea; lankters were present, the highest formed Amphipoda: Urothoe spinidactyla and by Copepoda (23 spp.), followed by 12 Erictlzonius brasiliensis; Chaetognatha: types of larval forms and 3 species of Sagifta enflata and S.bifunctnfa; Larval protozoa, 2 species each of rotifera and forms: copepod nauplii, cirripid nauplii, chaetognatha and 1 species each of fora- crustacean nauplii, gastropod veliger, minifera and decapoda. Almost a similar Tornaria larva, Metatrochophore larva, numerical pattern with a total of 59 groups Echinispira larva, polychaete larva, shrimp were recorded in station 2 represented by eu~hausid'Oea, Protozoea, copepoda (28), larval forms (16), proto-

( +Station 1 (

Fig. 12. Monthly variations in population density Fig. 14. Monthly variations in species evenness Diversity of Zooplankton in Parangipettai coastal waters 149

salinity and negative correlation with 1 - dissolved oxygen at both the stations (Table 1). Species diversity of zooplankton var- ied from 1.83 to 3.96 at station 1 and 1.89 0.85 to 4.01 at station 2 (Fig.13). Species even- 0.8 ness ranged between 0.59 and 0.93; 0.77 0.75 and 0.94 at stations 1 and 2 respectively 0.7 (Fig.14). Minimum was recorded in the P>00 A 9 - + monsoon season and the maximum dur- aJes$Qj3 a V) C, ing summer season. Species richness var- Fig.15. Monthly variations in species richness ied from 0.80 to 0.94 and 0.80 to 0.96 at stations 1 and 2 respectively (Fig.15). At zoa (51, rotifera (21, amphipoda (2), both the stations minimum and maximum chaetogna tha (2)r tera tes richness values were recorded during the ctenophora (I), foraminifera (1) and monsoon and the summer seasons respec- decapoda (1). Figures 10 and 11 give the tively . percentage composition of zooplankton at station 1 and 2 respectively.

Table 1. Population density in relation to various parameters Station Station 2 Parameter Population density Parameter Population density r value P r value P Temp. Temp. Salinity Salinity DO DO pH pH Nitrate Nitrate Nitrite Nitrite Phosphate Phosphate Silicate Silicate

The population density of zooplank- Discussion tonic organisms varied from 560 to 87,780 The physico-chemical parameters such No./m3 at station 1 and 184 to 1,56,164 as temperature, salinity, dissolved oxy- No./m3 at station 2 (Fig.12). The maxi- gen, pH and nutrients showed seasonal mum population was observed during the variations. The bulk of rainfall was ob- summer season and the minimum during tained during the northeast monsoon at the monsoon season. The zooplankton both the stations and the pattern of rain- population density showed a positive fall influenced the physico-chemical and correlation with water temperature and biological characters of the study area. 150 P. Sanl-hanam and P. Perumal

The high temperature during summer as they are least tolerant to higher salinity at both the stations can be attributed to (Govindasamy and Kannan, 1991). The high solar radiation. The low temperature tintinnids were absent during the mon- during monsoon could be due to strong soon season because of high freshwater land sea breeze, rainfall and cloudy sky. input while the hydromedusa, ctenophora, The high salinity values noticed during chaetognatha and Lucifer spp. were re- the summer months could be due to the corded during period with high tempera- high solar radiation and neritic water ture and salinity showing their wide tol- dominance (Thangaraj, 1984). The pH was erance to these hydrological parameters. low during monsoon season due to the Fish eggs and larvae were abundant influence of freshwater, reduction of sa- during the post as well as pre-monsoon linity and decomposition of organic mat- seasons indicating their seasonal distribu- ter. During summer season pH was high tion . because of the uptake of CO, by phy- toplankton. Similar observations were The high zooplankton population den- made earlier by Santhanam, 1976; Santha sity during the summer season could be Joseph, 1975, 1982 and Sivakumar, 1982. related to the stable hydrographical con- The high dissolved oxygen concentration dition while low density during the mon- was due to the phytoplankton photosyn- soon season is attributed to heavy flood thesis. and freshwater inflow (Santhanam et, al., The inorganic nutrient concentration 1975; Shanmugam ef al., 1986; Kumar, was always higher during monsoon sea- 1993 and Rajasegar, 1998). The density of son due to heavy rainfall, land drainage the zooplankton was comparatively high and input of fertilizers from the catch- at station 2 in the estuary than at station ment areas and low during other months 1 in the sea. The estuary gets more or- due to utilization by phytoplankton ganic matter from catchment areas (Krishnamurthy, 1961 and Santhakumari, (Subbaraju, 1970 and Kumar, 1993). The 1971). observed high summer biodiversity could The copepods were the dominant again be related to stable hydrological group throughout the study period in the parameters, which induced the denser sea and estuary, which may be due to the production of many species. But during plentiful food availability as well as due the monsoon season the freshwater flow to their continuous breeding and high played an important role in the reproductive capacity (Kumar, 1993). hydrographical changes that reduced the Maximum numerical counts of the cope- species diversity. pod population have been reported when References the temperature and salinity were high in the environment (Rajasegar, 1998). Chandran, R., 1987. Hydrobiological studies in the gradient zone of the Vellar estuary. IV. Benthic Rotifers were observed during the fauna. Mahasagar, 20: 1-13. monsoon and the post-monsoon seasons Diversity of ~ooplanltonin Parangipettai coastal wafers 151

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