Occurrence and seasonal changes in the distribution of two cladocerans in the eochin Backwater, Evadne tergestina Claus and Penilia avirostris Dana have been considered. Fluctuations in temperature of tbe estuary are of the

order of SoC., while tbe cbanges in salinity are considerable. Seasonal variation in distribution of tbe two species bas been correlated with temperature

and salin ity in T-S-P diagram for a period of fifteen months. Their numerical abundance month-wise bas also been investigated. A comparative study of the distribution of cJadocerans of the insbore waters of India wilh that of the

Cochin Backwater has also been carried out

Pillai, M Ayyappan

Pillai, P P

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128 P. Param~swarall Pillai and M. Alyappan Pillai METHOOS The region and details of sampling has been dealt with elsewhere (Pillai e/ 01., 1973). Zooplankton samples collected at weekly intervals for a period of fifteen months (December, 1969 to February, 1971) were analysed and the cladoceran component of the samples so rted out, identified and counted up to the species. Measurements of temperature and salinity we re made from the same station along with the zooplankton samples. HYDROGRAPHY The annual rainfall in the Cochin Backwater is abollt 3.2 cm with fluctuations noticeable from year to year. The influence of the freshwater runoff on the hydrographical properties of the Cochin Backwater is con-siderable. Surface temperature evinced a bimodal distribution during the course of the period (Fig. I). Temperature values decreased by the onset of monsoon and maximum tempe rature was recorded during pre-monsoon period. The range in temperature values was 27.6 - 31.3·C. (August and April respectively). Surface salinity showed maximum variation and fluctuated between I. 36 %. (July) to 34.53 %. (Apri l) (Fig. I). The commence-ment of the decreasing trend coincided with the onset of monsoon and during post-monsoon period a gradual rise in salinity values was observed. By the pre-monsoon months, maximum va lues were recorded. Q UANTITATIVE DISTRtBUTIOK Three species, Evadne tergestina, Pellilia aviroslr;s and Podon sp. were recorded during the present study, but the former two species make up the majority of the cladoceran component of the zooplankton and as such the seasonal fluctuations in their dist ribution has been dealt with separately in this report. El'adn~ (uges/ina Claus (Figs. I , 2a) Members of this species were observed in the samples almost during all the seasons except the monsoon months of May a nd June (Fig. I). They were common in the plankton collected during December, 1969. After a short diminution in January, 1970, tbey recorded a numerical increase during Feb ruary since when a decline in their number was noted. They we re absent in the plankton during May and June. This species reappeared in the sanlples in July and the period of their peak occurrence was the intermediate post.monsoon months. During September, maximum numbers (8187/m3 ) were recorded and during this period females were observed to carry brood pouch with eggs. After October, 1970, their number dwindled in th e plankton ( Bull. Dept. Mar. Sci. Univ. Cochin, 1975. VIl, 1, In-I36. ECOLOGY OF THE CLADOCERANS OF THE PLANKTON COMMUNITY IN THE COCHIN BACKWATER P. PARAMESWARA~ PILLAl AND M. AYYAPPAN PILLAI Central Marine Fisheries Research Institute, Cachin·682018 ABSTRACT Occurrence and seasonal changes in the distribution of two dadocerans in the eochin Backwater, Evadne urg£>stina Claus and P~nilia Qviroslris Dana have been considered. Fluctuations in temperature of tbe estuary are of the order of SoC., while tbe cbanges in salinity are cons iderable. Seasonal variation in distribution of tbe two species bas been correlated with temperature and salin ity in T-S-P diagram for a period of fifteen months. Their numerical abundance month-wise bas also been investigated. A comparative study o f the distribution of cJadocerans of the insbore waters of Ind ia wilh that of the Cochin Backwater has also been carried out. Although va rious groups of zooplankters occurring in Cochin Back-water have been investigated in detail , comparatively little attention has been paid to study the species composition and ecology of cladocerans of this area. George (1958) in his pioneering studies on the planktoh distribu-tion in the cana ls and the co nnected estuarine waters around Cochin recorded the presence of Evadne rergestina Claus as the common cladoceran of the canal plankton. Nair and Tranter (1972) opined that cladocerans were present towards the mouth of the estuary and were conspicuous by their absence during the post-monsoon period. Menon et 01. (1972) observed that the members of the genera Evadne and Pen ilia were ' the dominant representatives ' of the cladocerans of the zooplankton of Cochin Backwater. The present investigation is aimed at understanding the species composition of cladocerans in the estuarine wate rs around Cochin, their seasonal distribution and succession in re lation to hydrographic features and com· parison of their quantitat ive distribution in the estuarine and neritic waters along the west cost of India. We are grateful to. Dr. E. G. Silas , Director, Central Marine Fisheries-Research Institute for the encouraging guidance and for the critical suggestions during the course of ihis stud y. Ecology of Ihe cladocerans of Ihe plankton communily 129 collections and in December only few specimens we re observed. As recorded previously they were numerically high during February, 1971. Pen ilia avirostris Dana (Figs. I, 2c) During December, 1969, this species was observed in the plankton and they were absent till August, 1970. Thei r reappearance in August was followed by their numerical peak during October, thu s outlasting the pea k occurrence of E. t~rg~stjna by a few weeks. They were quantitatively less during December, 1970 and few specimens were recorded during February , 1971. Most of the females recorded were parthenogenet ic females although sexual females and males were also present in the collections. DISCUSSlo" Seasonal cycle and quantitative distribution George (1958) recorded E. lergestina in considerable numbers in the Cochin Backwater during July , August and September and less numerically in October. He also commented that they were absent during the high salinity period from November and according to him the entry of these forms from the neighbouring coastal waters to the estuar ine area may either be due to their abundance in the inshore wa ters during the post· monsoon period or due to their active breeding habits. Nair and Tranter (1972) recorded c ladoceran s from the mouth of the estuary and stated that 'they were conspicuou s by their absence towards the head of the estuary during the pre-monsoon periods ' . However. Menon" al. (1972) observed c1ado-cerans at Aroor, a typically estuarine habitat during both high and low salinity periods. Present observations show that the distribution of c1ado-cerans, especially E. tergestina is more or less year round and their peak occurrence coincided with the post.monsoon months of September to October (Fig. I), wh ich are in concurrence with the observation of Menon el al. (1972). Out of the four species of cIadocerans recorded from the Indian Ocean , viz. Evad,,~ Urges/ina, E. spim!era, Podon polyphemoides aDd Penilia aviro$/ris, E. lerges/ina is widely distributed in both the coastal and oceanic waters and the other sptcies are restricted mostly to the coastal waters. Further, Nair el al. (1913) reported that the peak abundancc of cIadocerans was noticed (900jhaul) off Cochin, Goa , Gulf of Cambayand Karachi Coast. According to Della Croce and VeDugo pal (1972) E. lugeslina is present discontinuously throughout the year in costal waters of Arabian Sea where it reaches high density populations in some area s in November. During March to May this species was observed in offshore waters indIcating of seaward transport during the monsoon transitional period. From the Madras Coast Rajagopal (1962) recorded the maxima of E. lergeslina during March to 130 1 10 P. Parameswaran Pillai and M. Ayyappa/l Pilla; i::M?ERATUR[.OC ZJOPlANKTON BIOMASS mthOO'm3 ... 3 10 2 10 PENILIA AVIROSTRIS No/100m3 ( tog. scale) .lVA ONE iERGESTINA "'/10000 ( log.scatQ) Fig. I. Monthly distribution of Temperature , Salinity, zooplankton biomass and mean (monthly) numbers of Evadne lerg<slina and Peniila avirostris in the Coch in Backwater during December, 1969 to February 1971. Ecology of the cladocerans of Ihe planklon communily 131 May. Vijayalakshmi and Venugopalan (1972) observed Penilia aviroslris during a single season (March to April) with a peak occurrence in April. One characteristic feature observed during the present study on the distribution pattern.s of cladoceraos is that the commencement of their swarming is as abrupt as their tapering off. This may be due to the fact that they reproduce in successive generations quickly, by active and efficient parthenogenesis in addition to amphimetic reprodu~tion. According to Wickstead (1965) 'for the greater part of the year they will be absent. Then , when the resting eggs hatch one or two will be caught. After this the numbers will increase rapidly. Within six months or so Pen ilia can range from being completely absent to being present in numbers like 2500j m3 forming over fifty percent of the plankton in number ' . According to Vijayalakshmi and Venugopalan (1972) maximum of P. aviroSlris was recorded in the Porto Novo waters during April, which coincide with the month of diatom abundance (diatoms 528 x 103 celJs jm3). The population lasted fo r a period of only three months . Parthenogenetic females were common than males and sexua l females which constituted only 3% and 0.4% of the total Pen ilia population suggesting that cyclical parthenogenesis occurs at tbe Porto Novo waters . Such rapid numerical increase and waning out has been reported to be more or less regul ar at different areas in the coastal waters along the west coast of India (George, 1953; Ramamurthy, 1965; Mukundan , 197 1). T - S - P relationship (Fig. 2 b, d) E. tergtstina and P. avirostris exhibit distribution patterns which seem to depend on the local hydrographical conditions. Earlier records on the occurrence of c1adocerans in the Cochin Back water in relation to salinity show tbat they a re recorded in a wide range of salinity (George. 1958: 2.00 to 11.00 %.; Menon el al., 1972: (\.6 to 32.8 %.). Present study on tbe temperature-salinity relationship of the two species of ciadocerans shows that P, avirostris is more restricted in distribution, while E. tergeslina occurs in a wide range of salinity, both tbe species showing abundance during the period when the sa lin ity and temperature values are relatively low (Fig. 2 b, d). P. avirostris was observed to prefer low temperature of the environment and they were recorded wilhin a temperature range of 26.5 - 30.0'C. Ramamurthy (1965) recorded the occurrence and abundance of ciadocerans in the coastal plankton of the North Kana ra waters and according to him E. lergestina would appear to prefer a lower salinity (16.17 - 3().94 %.) than Pen ilia (29.()0 - 33 .56 %. ) . Della Croce and Venugopal (1972) reported the occurrence of P. aviroslris off Bombay Coast at a surface temperature of 30.18'C and 8.rC. rema ining the lower limit. Vijayalakshmi and Venugopalan (1972) 132 P. Param.swaran Pillai and M. Ay)"appan Pillai observed that P.nilia occurred in the plankton within the salinity range of 31.8 - 33.9 %. and temperature range of 29.0 - 31.0·C. According to Outta et al. (1954) , for freshwater cladocerans temperature between 21 - 2ZOC. accompanied with low turbidity, is presumably most favourable for their occurrence. During the present observation we have noted the occurrence of P. avirostris and E. t~rgestina in lo\\'er salinities as low as 11.09 fr, o' This difference in observation may be due to the fact that in the estuarine environment extensi ve fluctuations in sa linity values were observed whi le in coastal waters such extreme va lues are seldom met wi th. However, no decisive conclusion could be drawn on the tolerence of these spec.ies to different sa linity gradients as only limited data is available. s 0 IS '" ~ 30 " S 1() 15 '" '" b 0 d .~ :n 0 31 31 0 F-· 0 00 30 .00 30 0 0 0 o~ 29 29 0 0 0 ,. 0 • 29 , 0 • 27 " " 0 0 s <> 5 20 2S 3D .3S 5 <> ·s 20 2~ :>:> " o- OCCURRE NC £ 5 • N T Y ( .~ ) . _,:: SIvNDAi\C:: Fig.2. a. Evadne tergestina Claus, lateral vi ew; h. T - S - P relation of E. tergestina; c. P~nilia avirosrris Dana , lateral view ; d. T - S - P relation of P. al'irOSlris (open circles indicate their occurrence and closed circles their abundance). An interesting parall el could be observed in the quantitative distri-bution of cladocerans in the neritic waters and in the estuaries. Pill ai and ·Pillai (1973) whi le studying the tidal influence on the diel variations of zoo-plankton in the Cochin Backwater observed that a clear relati onship is evident between the abundance of cladocerans and tidal variations in the Ecology of the cladocerans of the plankton community 133 estuarine area. A comparative study of the previous records of tbe distrj. but ion patterns of cladocerans in the inshore waters of the west coast of India reveals 'that they attain maximum occurrence and abundance both in the sea and in the backwater at more or less the same time. The period of their abundance previously recorded at various centres along the coastal waters of the west coast of India is during the post-monsoon mODths of September - November (Table 1). Pillai (1970) observed that c1adocerans were fairly abundant in the plankton of Bombay Coast during May and according to him 'in no other samples they occur in noti~eable numbers '. The significance of such an early attainment of their abundance is not apparent in the light of the hydrographic data, the values of which were maximum during May (Temperature: 30·0·C; Salinity: 36.20%. ) . However, Bharga"a.t 01. (1973 ) observed c1adocerans along Panaji - Bombay Coast during September to January and Della Croce and Venugopal (1972) recorded the ir abundance at Bombay during November - December period. It is also apparent that there is a south . to north movement of cladocerans along the west coast of India which is evident from the reports of their distribution and abundance during different months of the year from various Centres along the coast. Table I. Periods of peak occurrenc~ of c1adoctrans 01 different cen/us along rite coastal waters of India Location Madras Coast Porto Novo waters Trivandrum Coast Cochin Backwater Calicut Coast North Kanara Coast Panaji to Bombay Coast Bombay Coast Coastal waters of Arabian Sea Author (s) Rajagopal (1962) Vijayalakshmi and Venugopalan (1972) Menon (1945) George (1958) Menon et al. (1972) Present study George (1953) Mukundan (1971) Ramamurthy (1965) Bhargava <I al. (1973) Pillai (1970) Della Croce and Venugopal (1972) Della Croce and Venugopal (1972) Peak puiod (s) March - May March - April July, October August - September September September - October September - Octo ber July, October September - October September - January May November - December November 134 P. ParameslI"aran Pillai and M. Aryappan Pillai The coincidence of the cladoceran maximum with that of the other groups of the zooplankton community was also observed in the Cochin Backwater. After the monsoonal decline in population , copepods in the Cochin Backwater evince a gradual rise in number and biomass during the months of September - November when their secondary maximum was noticed (Pillai el al., 1973). During this period fi sh eggs and larvae were recorded in maximum numbers indicative of active breeding of fishes. The relationship of mackerel fishery or the west coast of India to the abundance of cladoeerans has been reviewed by Selvakumar (1970) and according to him, the movement of cladocerans is followed by mackerel shoals from south to north during late monsoon. With the avilable information it is difficult to ascertain the exact nature of the migratory behaviour of macker~l s in relation to the abundance of cladocerans since the former involves various environmental factors as we ll. However, the coincidence of the abu ndance of cladocerans during this period is noteworthy as simi lar abundance has been reported from the Calicut Coast (George , 1953: Mukundan, 1971), and as opined by George (1953) 'cladoeeran maximum also coincides with the peak fishery along the Calicut Coast and the cladoeerans have been observed to form the important food of the shoaling fishes ' . Bhargava, R. M. S. , R. A. Selvakumar and S. Y. S. Singbal Della Croce, N. and P. Venugopal Dutta, N. , J. C. Malhotra and B. B. Bose George, P. C. Geo rge , M. J. Menon , M. A. S. REFERENCES 1973 Hydrobiology of surface waters along Panaj i-Bombay Coast Indian J. mar. Sci., 2(2), 103- 107. 1972 Distribution of marine cladocerans in the Indian Ocean. Mar. bioi., 15(2), 132·136. 1954 Hydrology and seasonal fluctuations of the plankton in the Hoogly Estuary, {PFC Proc., 35-47. 1953 The marine plankton of the coastal waters of Calicut with observations on the hydro-graphica l conditions. {ndian J. Fish., 5(1) : 76-107. 1958 Observation on the plankton of the Cochin Backwater. Indian J. Fish. , 5(2), 375-401. 1945 Obse rvation on lhe seasonal distribution of the plankton of lhe Trivandrum Coa st. Proc. !"dian Acad. Sci .. 22: 31 - 62 . Ecology of th, c1adoarans of the plankton community 135 Menon, N. R., P. Venugopal and S. C. Goswamy Mukundan, C. Nair, K. K. Chandrasekbaran and D. 1. Tranter Nair, K. K. Chandrasekharan, Jacob George and T. S. S. Rao Pillai, V. Kunjukrisbna Pillai, P. Parameswaran and M. Ayyappan Pillai 1972 Total biomass and faunistic composition of the zooplankton in the Cocbin Backwater. J. mar. bioi. Ass. India , 13(2), 220-225 . . 1971 Plankton of Calicut inshore waters and its relationship with c.oastal pelagic fisheries. Indian J. Fish., 14,271-292. 1972 Zooplankton distribution along salinity gradients in the Cocbin Backwater before and after the monsoen. J. mar. bioi. Ass. India , 13(2), 203-210. 1973 Distribution of certain planktonic crusta-ceans and insect Halobates in the Indian Oceac. Indian J. mar. Sci. , 2(2) , 116-121. 1970 Observation on tbe plankton of Bombay Coast with remarks on tbe hydrographic conditions and fishery. J. mar. bioi. Ass. India. 10(2), 237-245. 19 73 Tidal influence on the diel variations of zooplankton witb special reference to cope-pods in the Cochin Backwater. J. mar. bioi. Ass. India, 15 (1), 411-417. Pillai, P. Parameswaran , 1973 S. Z. Qasim and Copepod component of zooplankton in a tropical estuary. Indian J. mar. Sci., 2 (I ) : 36-46. A. K. K, Nair RajagopaI, P. K, 1962 Notes on the occurrence of cladocera in the Madras coastal waters. Curro Sci. , 31 , 467-468. Ramamurthy, S. 1965 Studies on tbe plankton of the Nortb Canara Coast in relation to tbe pelagic fisbery. J. mar. bioi. Ass. Iadia, 7 (I), 127-149. Selvakumar, R. A. 1970 Cladoceran swarm in relation to mackerel fisbery along .tbe west coast of India. Curro Sci., 39, 481-482. 136 P. Parameslraran ' Pillai and M. A vyappan Pillai Vijaya la kshmi . G. S. and V. K. Venugopalan Wick stead, J. H. 1972 Occurrence and fertility of Penilia avirostris Dana (Cladocer. ) in Porto Novo waters. Indian J . mar. Sci. , I (2), 125-127. 1955 An introduction to the stud y of tropical plankto n. Hutchinson tropical Monograph, pp. 1-160. 181 figs . 

Ecology of the cladocerans of the plankton community in the Cochin backwater

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Ecology of the cladocerans of the plankton community in the Cochin backwater

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