The meroplankton comprising 20-40% of total zooplankton composition, were mainly represented by decapod larvae, polychaetae larvae, bivalve veligers and ...
Indian Journal of Marine Scien..:es Vol. 28, June 1999, pp. 192-197
Distribution of zooplankton in relation to water movements in Kakiinada bay, east coast of India P Chandra Mohan, A V Raman & N Sreenivas
Division of Marine Biology, Department of Zoology, Andhra University, Visakhapatnam 500 003, India Received /9 June /998, revised 28 January /999
Plankton collections were made from three stations in the bay to study the annual variations in distribution of zooplankt on in relation to temperature, salinity, turbidity , pH and dissolved oxygen. The annual mean value of biomass and numerical abundance at three stations were 1.79, 1.80, 2.91 ml.m·3 and 38482, 39269, 38447 no . m ·l respectively at three stations. The prevailing northerly and southerly currents along the coast also inf1uence the di stribution of the planktonic organisms. In spite of these wide fluctuating conditions we can distinguish characteristic populations within the bay region which show regular annual cycles and colonization. Marked depletion in the number of species was observed during the last 2-3 decades on account of deterioration of water quality of the bay, which is known to receive effluents from the adjacent industries and city.
The Kakinada bay (long. 82°14' - 82° 22' E and lat.J 6°5' - 17°) is situated on the east coast of India, about 160 km southwest of Visakhapatnam. It is the main' receptacle for the river run off of the Godavari estuarine system. The total areal of the bay is 132 km 2 . Two major di stributeries of the river Godavari, Coringa and Gaderu open into the Kakinada bay. Other small channels viz., Chollangi, Mattlapalem and Pillavarava also open into the bay on the south· western and south - eastern comers respectively. On the eastern side of the bay, there is a long narrow sand bar continuou s with the eastern tip of the Hope islar.d separating the bay from the sea. Due to the presence of the sand bar, the Kakinada bay forms a semi-enclosed body of water where the water movements are unique. Two types of circulation patterns are seen in the bay. The water movements are coupled with the salinity distribution in. the bay which in tum limits the plankton distribution. St}ldies made on the distribution of zooplankton in relation to water movements, in Sundays river estuary in· Algoa Bay,2 and Mandovi - Zuari estuarine system3 revealed that the zooplankton distribution is dependent on the water-mass movements. In the present investigation an attempt was made to identify the plankton distribution and also the , variati o ns in the numerical abundance of the plankton due to the prevailing hydrographical conditions and in particular the currents in the Kakinada bay.
Materials and Methods Surface zooplankton samples were collected from three stations in the Kakinada bay (Fig . !) at monthly intervals during July 1995-June'96. The zooplankton 15'
82
20'
1
4
3
17'
o·
-'
Z ILl
III LL 0
>1
~ovember
C l.m"C.r\t Period )
Fig 3-Prevailing waler mo vements in relation to the current patterns in Kakinada bay.
15' S~
196
INDIAN J. MAR. SCI. VOL. 28, JUNE 1999
area the entire Kakinada bay area' can arbitrarily be divided into two zones: Zone I-The marine dominant area representing the northern bay which is the zone where reproduction, growth and maturation of plankton populations takes place: represeoting mostly the holoplankton groups in the plankton collection (station I). In general in thi s region holoplankton abundance was more. Immigration of larvae suc h as Crustaceans, Bivalves and Gastropoq veligers from the southern region of Kakinada Bay was often encountered.· In this zone ' the dominant holoplanktonic groups were Copepods, Lucifers, Chaetognat hs, Hydromedusae: Siphonophores, Appendicularians, Ostracods, C ladocerns and Pteropods (Table 2) . Among the meroplankton the dominant groups were Decapod larvae, Bivalve and Ga~;tropod veligers~ Polychaetae larvae. Zone II- The brackish water domjnant area located in the southern part of the bay which is the main region for the rec ruitment and colonization and supports mixed populations in the plankton sample. Thi s area was dominated by brackish water and is located in the sout hern part of the Kakinada bay (station II and III), which seems to be the main area for th e seasonal recritment and col011ization . This zone support s' mixed zoop lankton populations . Among the meroplankton Gastopod and Bivalve
veligers and Po]ychaetae larvae were abu ndant along with the Decapod larve. In this zone there seem to exist a typical seasonal pattern of distribution in the plankton abundance, and the abundance showed two peaks during premonsoon (July'95, 114970 no .m-3) and a minor peak during the postmonsoon period (February'96 , 53045 no. m-3) . Distribution of major groups of zooplankton populations were governed by various. behavioural and physiological adaptations of the plankton popu lations to ever changing hydrographical conditions. Wooldridge & Erasmus 2 from the Sundays estuary (South Africa) reported that behavioural adaptation s include utili zation of tidal currents, ve rti cal mi gration of zooplankton in well-stratified es tuari es. The meroplankton decapod larvae are able to ()ti Iize tid al currents for their horizontal di stributi on l 415 . The prevailing circulation and water mixing process in the semienclosed Kakinada bay seems to influence the distribution of plankton populations. The distribution of various plankton groups was also influenced by rainfall to some extent during the mon soon period. Relatively high fre sh water runoff during mon soon provides embayment with a large amount of nutrient s which allowed the development of phytoplankton community' 6, this inturn may result in the production of herbivorous zooplankton, mostly
Table 2-Percent age composition of holoplankton and merop lankton at th e three selected stations
Holoplankto n Meroplankton
Min
Station I Max
Mean
Min
Station 1\ Max
Mean
Min
Station III Max
Mean
54.49 11 .5 7
88.43 45.51
70.60 29.39
53.49 8.12
81.46 46.51
72.46 27.42
53.42 17.12
81.62 46.58
69 .05 30.90
Table 3-Variations in the zooplankton characteristics in the study area over 40 years period Parameter Min
DuriI'lg 1958 -60 Max
Mean
Min
Present studi: 1995-96 Max
Mean
19
Displ. volume (cc)
2.00
406.00
74.71
1.5
19
6.08
Numerical abund ance Dominanl zoop/anklon species Co pcopda Other crustaceans Coe lenterates Mysidacea C ladocern s Chaetognaths Other grouEs
185
53645
8739
976
11497
384 1
60 3 17 12 4 5 II
42 3 14 8 2 8 19
r '
CHANDRA MOHAN et a/. : DISTRIBUTION OF ZOOPLANKTON IN KAKINADA BAY
197
~
meroplankton in nature. The present investigation was in confonnity with the investigations carried out by Mathew et at. 17 from the EEZ who reported higher biomass and abundance of zooplankton from the Kakinada area. The characteristic phenomenon that enables the organisms to survive in particular zone or biotope is highly appreciable and it may be due to the mechanism that generates environmental variability for animals in estuaries. The first component corresponds to the presence of longitudinal and vertical gradients in physico-chemical parameters, and the second component is the dynamic environmental variability results from the water movements which'determine the rate and direction of changes In abiotic conditions an individual . 18 expenences . In the present study a comparison was made with the earlier study carried out by Chandra Mohan l9 . It is int~resting to note the marked depletion in the species number of different zooplanktonic organisms on account of changes in topographical . and hydrographical features of Godavari estuary which may bring about drastic changes in the water quality. The number of species of major zooplanktonic groups encountered during the present investigation and during 1958-60 study was. given in the Table 3. The distinct depletion in the numerical abundance and species diversity may be attributed to the changes in the water quality due to effluents discharge and other anthropogenic factors during the last three decades.
Acknowledgement The above study is a part of the investigation carried out during 1994-97 in a research project
sponsored by C.E.C (Belgium). One of the authors (NS) is thankful to the csiR, India for the financial assistance (as Senior Research Fellowship) received during the study period. .
References I 2 3 4
5 6
7 8 9
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