Indian Journal of Marine Sciences lffect Vol. 3, December 1974, pp. 135-138 food owth Irob- .t of Species Distribution in Aquatic Environment

K. KRISHNAMURTHY, R. SANTHANAM & V. SUNDARARAJ , for Centre of Advanced Study in Marine Biology, Marine Biological Station of Annamalai University, Porto Novo 608502 has Received 30 March 1974; revised received 19 August 1974 vliss) ssis- An intensive study of from March-July 1973, when hydrographic conditions were relatively stable, was carried out in 3 different aquatic biotopes of Porto Novo. Maximum number of species (34) was noted at backwater station 3 and the minimum number (18) at mangrove station 1. However, were rich in estuary (station 7). Tintinnids Biol., (Protozoa: Ciliata) were rich in backwater. Maximum number of species (9) iques was found in backwater; estuarine stations ranked next (8 species). Total number of species 5. N. (denoted as species diversity) found in a biotope was empirically related to variations in tion) , standard deviation of salinity, copper concentration of water, changes in percentage of chloro- phyll a (in total chlorophyll) and to planktonic circulation. Maximum daily increase of diatom n&a, population was in the estuary (station 7 = 1.85 x 106 cells/m3) and the minimum was in the mangrove (station 1 = 1.21 x 103 cells/m3). rthos, hell 207. PECIES distribution in marine environment variations of salinity. Variation in salinity values ian). is determined by a combination of various (covering present study and supported by earlier Yaki.. S factors. Opportunities exist for studying annual studies) at a station is expressed in terms aspects of planktonic species distribution in various of standard deviation (SD) which is used as a aquatic biotopes in and around Porto Novo. Most measure of index of diversity. Influence of low niya of these biotopes are under neritic influence to a tide during the period of predominantly neritic 7-30 Fish. greater or lesser extent. The present study is water influence in the estuary and backwater is made during March-July 1973 in 3 biotopes, estuary, assumed to be not very significant. During this 11. 6, backwater and mangrove forests (Fig. 1). period salinity variation between tides was not n& great ; and the flow of freshwater in the system, Materials and Methods . H. if not totally absent, was negligible. Species diver- Intensive plankton collections were made quanti- sity in the present study denotes total number of tatively using a bolting silk No. 20 net. Counting species found (greater the number of species, higher )73), of aliquots of plankton after proper fixing in for- the species diversity). .,’ in malin was carried out using Utermoehl inverted :r & microscope. Usually weekly two collections (at shorter intervals also whenever possible) were made at high tide covering all the stations in one excursion. Any errors in sampling due to patchiness of plankton rrch, distribution, variability in net hauls, mesh size ldon of nets, randomness of collection, etc., may be assumed to be evened out, as between stations, since the study was based on intensive collections spread over the most stable period. The sampling

*on- variations were assumed to be not great enough tifiC to materially affect the overall picture due to con- sistency of collection, sampling, etc., over the period. M., Results and Discussion 5. Salinity values did not fluctuate much between OP., stations during the period of study (Table 1). With ratic great influx of neritic water and in the absence of tuk. external influences like flood or rain, more or less Seas stable and uniform conditions prevailed during 978, this period. On the basis of relatively stable condi- Marine eiological sation 33 tions approximating neritic waters, the regions may be graded based on the salinity standard as Beds of Mudflab 6.5. Estuary

At mangrove stations, the total number of species percentage of ‘ living ’ chl. a of water (in total chloro- At s found were fewer. In the backwater situation, phyll) would indicate the relative nature of species acli where salinity was relatively stable, more species composition. This relationship between species com- diatc were found. On the basis of the magnitude of position and chl. a percentage was inverse. Higher in 01 species composition, the biotopes may be arranged the species diversity, a lower percentage of chl. a This as Backwater>Estuary>Mangrove. was found. At backwater stations, greater species larv; Maximum number of species encountered during diversity led to a decrease in chl. a percentage and latio the study period was 34 (Table 1). Number of vice versa. Maximum variation in chl. a percentage othe species in mangrove was low and often less than was at backwater stations (particularly stations light that in the other two biotopes. The temperature 3 and 4) and the minimum was at mangrove stations At was between 27.00 and 33.50C. An inverse empirical (particularly station 1). An increase in chl. c was pred relationship was observed between species' occur- associated particularly with Ceratium trichoceros diatc rence and standard deviation of salinity which was and Planktoniella sol (particularly at station 3). PoPr also supported by previous studies during 1971 Copper versus species diversity - Like variation at tl and 1972. It is well known that, in an estuary, the in salinity, copper (dissolved ionic) concentration Di number of species gradually increases from its of water was also found to exert an influence on was fresh water to neritic water end1 (Table 1). species diversity. In mangrove where copper values to a At station 3, where salinity values were high were higher5 (Sundararaj, V. & Krishnamurthy, K., recn and SD of salinity was low, total number of species unpublished data) during January-February, rela- Diat observed was high. tive to summer months, fewer species (3) were found 21 J However, at station 7, though salinity values (station 1). During summer months when copper loss were almost the same as at station 3, and SD was concentration was low, more species (18) were found were also lower, the total number of species found was in mangrove region particularly at station 1. SPP. lesser than at station 3. This could be due to the In the backwater, where copper was lower than 3, 4 fact that certain species might be ‘ migratory ’ or in mangrove, more species were found (Table 1). danc ’ autochthonous ’ or thrive only under certain It is known that a negative correlation (Y =-0.88) >M; conditions. exists between salinity and copper in these waters. At Certain diatom species were found only in estuary. In recent studies the values of correlation coeffi- in i They were Melosira dubia, Hemiaulus sinensis and cients between copper and salinity were: (i) for and Rhizosolenia calcar-avis as at station 7. Amphiprora backwater, Y =-0.59; (ii) for mangrove, Y =-0.73. stati gigantea was found only at stations 3 and 8. The It follow; that, in fresh water, copper concentration factc species that was restricted to the backwater biotope is greater and the number of species is lesser. In are was Bellerochea malleus. Most of the species were an estuary (like the Vellar) more number of species to a common to most stations during summer due to are found in the marine zone than in the fresh water M; stability of hydrographic conditions in the water- zone. It may be due to the toxicity of copper Thei ways. exceeding a tolerance limit (which may vary be- flage Photosynthetic pigments versus species diversity - tween organisms)6. tions Relationship between the pigments (particularly Food chain relationships - Relation of tempe- flage chl. a, in total chlorophyll) and species, based also rature to metabolism and its resultant influence on were on earlier studies2-4 is worth considering. Changes in food chain links in an area merits attention. It is as in well known that (van’t Hoff’s law in general) higher Tl temperature, within limits, promotes the rate of 8. ’ metabolism of an organism. This is also cited as Estu was TABLE 1 -SALINITY,TEMPERATUREVARIATIONSANDSPECIES a reason for bigger size of an organism and late NUMBERS AT DIFFERENT STATIONS DURING MARCH TO maturity as more time is taken for growth in tem- CI JULY 1973 perate waters, and relatively smaller size and quicker 1 an (Range values are given in parentheses) maturity (for spawning and broods) in the tropics. At s Favourable temperature accelerates blooms of Al Biotope Sta- Salinity “I,, Tempera- No.’ of sp-ties certain diatoms6. Temperaturewise arrangement of crusi tion (mean* SD) ture, “C _------were No. Di- the biotopes will be : Mangrove> Backwater> (mean)I , Dinofla- the i atoms gellates Estuary. At station 1, temperature was higher than in the rest of the stations. Being a small vore Mangrove 1 33.7kl.07 32.1 18 8 enclosed area with thick vegetation around, high The (31.5-34.5) temperature causes excessive evaporation. Here ,Oithc 2 33.850.64 (32;:353.5) 26 7 the total number of species was less than the rest cam (33.0-34.5) (27.5-33.0) of the stations, and based on earlier studies, chl. a tion: to j Backwater 3 34.550.59 30.5 34 9 values were high. Phaeophytin a was also high (33.0-35.0) (up to 18 pg/litre) leaving aside only a moderate the I 4 33.8kl.06 (28+-3;~0) 29 9 proportion as ‘ living ’ chl. a. This was perhaps here (31.5-34.5) f28.0-33.01 due to grazing effect of and other zoo- whel 5 ‘33.7&09'1 ' 30.1 ~' 26 7 (32.5-35.0) plankton of the area. An intensive study of census siste 6 33.7hO.69 '275-3&~0) 30 9 of each species at different stations was made. diap (32.5-34.0) (28.0-31.5) This showed that wherever the population of diatoms I& was lower, particularly in the mangrove region was Estuary 7 34.6hO.30 29.4 30 8 cula (34.5-35.0) (station l), the populations of copepoda and crus- 8 34.Oh1.30 (27.&3;.0) 29 8 tacean larvae were higher. Frequently, at station 8, cula (30.5-34.5) (27.0:30.0) copepods and larvae were found in obse abundance. At station 5, tintinnids were abundant. fothi 136 KRISHNAMURTHY et al. : SPECIES DISTRIBUTION IN AQUATIC ENVIRONMENT

At station 7 diatoms were abundant. There was

a direct relationship between populations of the TABLE 2-CCALCULATEU DAILY INCREASE OF diatoms, and tintinnids. A decrease D IATOM POPULATION AT DIFFERENT STATIONS in one population was reflected in other ones also. This was not applicable for copepods and crustacean Station Increase of Dominant species NO. cells/m3 larvae as evidenced at stations 1 and 8. Popu- lations of plankton showed cyclical changes at all 3.4x10” Coscinodiscus spp. and Biddul- other stations. The population of a biotope throws phia mobiliensis light on the existing interrelations of organisms. 7.2 x104 Pleurosigma sp.. 9.6 x lo5 cuvvisetum and Cos- At station 1, the population of copepoda was ci~2odiscus spp. predominantly herbivorous consuming the available 2.2x105 Coscinodiscus spp. diatom crop. This grazing effect results in the 2.9 x lo5 Coscinodiscus spp. population balance tilted in favour of copepoda 4.2 x lo5 Khizosolenia stoltmfothii 1.8 x 106 C. cwuisetunz and K. stolter- at this station. fothii Diatoms were abundant at station 7. Salinity 2.4 x lo6 l‘halassiothrix fyauelzfeldii and was relatively very stable here. This contributed R. stoltevfothii to a relatively large stock of diatoms and to fresh recruitments from adjoining neritic area, sea. Diatoms were noticed at all stations between 21 June and 21 July 1973. There was not much and the minimum (1.21 x 103 cells/m3) at station 1 loss by way of grazing. The copepods present (when Coscinodiscus spp. and Biddulphia mobiliensis were mainly carnivores like spp. and Oithona were dominant). spp. The dinoflagellates reached maxima at stations An interesting food chain relationship was 3, 4 and 8. Regionwise arrangement of the abun- exhibited at different regions. A good diatom dance of dinoflagellates was: Backwater>Estuary crop appeared, followed by a rich population of > Mangrove. tintinnid at station 5; copepods at station 7; and At most stations, the dinoflagellate peak was crustacean : at station 8. As the crustacean in April-May. Only at two stations (stations 3 larvae and copepods, among others, began to feed and 7), it was during July. This late bloom at on the diatom, the diatom population was denuded. stations 3 and 7 was perhaps due to some limiting Copepods would move perhaps to new grounds factors in the environment. The limiting factors (nearby stations) where rich diatom crops were are being sorted out and it is too early to come observed and thus the diatom- sequence to a definite conclusion. would be maintained. Maximum population of tintinnids was at station 5. At stations 3 and 4 relatively sparse populations Their cycle of abundance was the same as for dino- of copepoda and crustacean larvae were noticed. . This was due to their food chain rela- Here the grazers were predominantly larvae and tionship as tintinnids are known to feed on dino- adults of oysters and larvae of other benthic and flagellates. The peak populations of tintinnids sessile organisms (like other molluscs, annelids, were found in March-April. At station 3 it was, etc., from nearby mudflats). Near station 3 there as in the case of dinoflagellates, during June-July. is an inlet. The ‘ water type ’ at stations 3 and The maxima of copepoda were at stations 1 and 4 appear to be essentially the same. Production 8. The pattern of abundance was: Mangrove> of diatoms at stations 3 and 4 was higher than the Estuary>Backwater. At most stations, the peak grazing encountered. was during April; at station 7, it was during July. . At station 7, diatoms enjoyed a surplus production Crustacean larvae were also high at stations due to grazing at low key. At station 1, however, 1 and 8. At most stations, the peak was in April. the situation was different; though diatom pro- At stations 2 and 7 it was in July. duction was high due to high predation, the popu- At station 7, the populations of copepoda and lation was denuded. crustacean larvae were relatively low. Diatoms Patchiness of at different stations were able to maintain their population levels, as could be attributed to a combination of many factors. the grazing rates of copepoda (predominantly carni- The present study indicates that the diatom com- vores) and other were within limits. munity could maintain its level of population by The available copepoda particularly Acartia spp. and a daily increase of 20% (by volume) at most stations. Oithona spp. showed that they were predominantly This was after sustaining losses due to biological carnivores to a larger extent, under natural condi- removal mechanisms like grazing, sinking, and tions. However, Oithona spp. have also been known mortality, and ignoring other factors. to feed on diatoms (in laboratory studies). So The Porto Novo waters (including near-shore) the effect of grazing on the diatoms was less distinct contain about 70 species of diatoms, 40 species of here. This was in marked contrast to station 1 dinoflagellates, 20 species of tintinnids and 70 species where grazing was intensive and population con- of free-living and pelagic copepoda. To these lists sisted mostly of herbivorous copepoda like Pseudo- additions are bound to be made with further in- diaptomus spp, vestigations. The norms regulating their distri- Rate of replenishment of diatom population butions are superimposed upon the closely interwoven was worked out for different stations and the cal- factors operating in the environment. culated values are given in Table 2. Highest cal- culated daily increase (1.85 x 106 cells/m3) was Acknowledgement observed at station 7 (when Rhizosolenia stolter- Authors thank Prof. R. Natarajan, Director, fothii and Chaetoceros curvisettum were dominant), for the facilities and constant encouragement. The INDIAN J. MAR. SCI., VOL. 3, DECEMBER 1974 authors (R.S. and V.S.) are gratefu1 to the UGC, 2. SUNDARARAJ, V. & KRISHNAMURTHY, K., Curr. Sci., 42‘ New Delhi, for the awards of junior research fellow- 3. SUNDARARAJ,(1973). 185. V. & KRISHNAMURTHY, K., J. exp mar. ships and one of them (V.S.) is indebted to CSIR, Biol. Ecol.. 14 (1974), 275. New Delhi, for the award of a senior research 4. KRISHNAMURTHY, K. bt SUNDARARAJ, V.. J. exp. mar. fellowship. Biol. Ecol., 14 (1974), 285. 5. SUNDARARAJ, V. & KRISHNAMURTHY, K., Curr. Sci., 41 (1972). References 6. SVERDRUP,31.5. H. U., JOHNSON, M. W. & FLEMING, R. H., MANGELSDORF, (Jr), P. C., in Estuaries, edited by G. H. The oceans, their physics, chemistry and general biology Lauff (American Association for the Advancement of iZ”ytice-Hall, Englewood Cliffs, New Jersey), 1942, Centr Science, Washington DC), 1967, 71.

very in thi taken, Mate: Ten mang on 3( shall0 canoe the I fOllOW and sampl grab. aseptj the rl labor: were I Total were PoPul 2216e phate and medit phate were their ammo Resu The very the a hydrc recorc sea ( salini