Four different size groups of algae were sampled from Cochin Backwater by passing sea

water through different grades of bolting nylon. C assimilation, chlorophyll (chl.) a concentration

and cell numbers of each size group were determined throughout the year along with

those of non-fractionated material. The contribution of nannoplankton, largely composed of

diatoms, was found to be much greater than that of microplankton throughout the year. Pooled

values of fractionated material agreed closely with those of non-fractionated material, but no

regular seasonal trend was found in photosynthesis, chl. a and cell numbers of any size group. A

greater dominance of nannoplankton as primary producers over microplankton seems relevant

to food chain considerations, as filter-feeding larval stages are probably able to utilize nannoplankton

more efficiently than microplankton

Balachandran, V K

Joseph, K J

Qasim, S Z

Vijayaraghavan, Sumitra

CMFRI Digital Repository

Indian Journal of Marine SciencesVol, 3, December 1974, pp. 146-149Contribution of Microplankton & Nannoplankton in theWaters of a Tropical EstuaryS. Z. QASIMNational Institute of Oceanography, Dona Paula, Caranzalem 403301andSUMITRA VIJAYARAGHAVAN*, K. J. JOSEPH & V. K. BALACHANDRANCentral Marine Fisheries Research Institute, Cochin 682018Received 4 May 1974; revised received 19 July 1974Four different size groups of algae were sampled from Cochin Backwater by passing seawater through different grades of bolting nylon. "C assimilation, chlorophyll (chl.) a concen-tration and cell numbers of each size group were determined throughout the year along withthose of non-fractionated material. The contribution of nannoplankton, largely composed ofdiatoms, was found to be much greater than that of microplankton throughout the year. Pooledvalues of fractionated material agreed closely with those of non-fractionated material, but noregular seasonal trend was found in photosynthesis, chl. a and cell numbers of any size group. Agreater dominance of nannoplankton as primary producers over microplankton seems relevantto food chain considerations, as filter-feeding larval stages are probably able to utilize nanno-plankton more efficiently than microplankton.FROM earlier studies it is clear that a greaterproportion of organic production in the sea(80-100%) 1 , is contributed by small formsor ' nannoplankton ' which pass through the netmade of finest mesh, as compared to ' microplank-ton ' or net plankton, which are larger and normallyretained by the apertures of the net". This istrue not only of neritic and oceanic waters 5 of bothtemperate and tropical regions 6 . 7 , but also of freshwater lakes"°. In polluted waters, the contributionof nannoplankton very often becomes many timesgreater than that of any other form of life", exceptperhaps fungi and bacteria.In an earlier communication dealing with theorganic production of Cochin Backwater, a quanti-tative assessment of phytoplankton. was made by14C uptake, chlorophyll measurement and countingmicroplankton retained by the ret 12 . Even inother studies where an estimation of phytoplanktoncrop was made by counting the organisms in groups(diatoms, flagellates and other algae) as part ofdemonstrating the influence of salinitv 13, nutrients'',or flushing rate'' in the backwater, the phytoplark-ton organisms smaller than 50 tan were largelyomitted. The earlier inference deduced from theproduction coefficient (ratio of gross production tocarbon content of phytoplankton) that the phyto-plankton crop sampled by the phytoplar.kton netcomprised only 1-28% of the total carbon assimi-lated 12, makes it necessary to investigate in greaterdetail the contribution of different size groups ofalgae in the total biomass. In this study, thephytoplankton communities were fractionated as apart of continued investigation on the hydregraphyof Cochin Backwater.*Present address: National Institute of Oceanography,Dona Paula, Caranzalem 403301Materials and MethodsWater samples from the surface were collectedat fortnightly intervals for a period of 1 yr (Sept.1972 to Aug. 1973) from a fixed station in theCochin Backwater. About 5 1 of water wasshaken up thoroughly and passed through boltingnylon materials of 99 (No. 14), 76 (No. 20) and 64(No. 25) p.m grades fixed to filtration discs mountedon a stand. The organisms retained by each gradeof bolting nylon were carefully rinsed with milli-pore-filtered sea water and collected in petri dishes.Each sample was made up to 500 ml for the esti-mation of '4C uptake, chlorophyll (chl.) a and cellnumbers of the organisms retained. Similarly, thewater which had passed through all the three grades_ofbolting nylon was also used for the above threemeasurements. In addition, the unfiltered waterwas also taken for these three estimations. Thus,in all, there were 5 different types of materials, viz.(i) algae of all sizes (unfiltered samples), (ii) algaelarger than 99 p.m, (iii) algae larger than 76 p.m, (iv)algae larger than 64 p.m, and (v) algae smaller than64 p.m.For "C assimilation, samples were taken inlight and dark bottles of 70 ml capacity andincubated with 5 Li.Ci of NaHCO 3 for 2 hr underconstant illumination of 10k. lux. Rate of produc-tion was estimated by the usual procedure. Chi. a.determinations were made using Whatman GF/Cpads and according to the method suggested byUresco 16 . For cell rumhers, about 50 ml of thesample was fixed with 5% formaldehyde solutionand allowed to settle in a chamber for 24 hr. Thesettled material was diluted to 10 ml, and aftermixing well, a sample of 1 ml was drawn and placedin Sedgewick Rafter counting cell and practicallyall the cells contained in it were counted.14612. . .J F MAMJ JA SOND160014ra• BOO• 42004.7. 150SO2416QASIM a al.: MICRO- & NANNOPLANKTON IN WATERS OF TROPICAL ESTUARYa Seasonal cycle of chl. a was somewhat differentfrom that of photosynthesis (Fig. lb). Peak valuesobtained from February to May were independentof a similar rise in the rate of 14C uptake indicatingthat much of the chl. a recorded during this periodwas not photosynthetically active. Probably it camefrom detritus or physiologically inactive algae. InMarch and April, the pooled values obtained fromfractionated samples were lower than those fromthe non-fractionated samples. This indicates thatthe inactive chlorophyll was largely contained inthe unfiltered sample. Similarly, the high valuesof carbon assimilation recorded in November andDecember were associated with only a slightincrease in chi. a content, although the formeragree well with the cell numbers (Fig. lc). Thisis probably because of the variations in the chloro-phyll content of the cells constituting the total algalbiomass. A similar variation in the chlorophyllper cell has been reported from the waters ofVineyard Sound 3 .Seasonal variations in the total cell numbergenerally corresponded with the seasonal trend inphotosynthesis (Fig. le), except for some months(January, April and August), when the counts showedminor peaks. This was largely because of relativepredominance of one or two organisms which formedder se concentrations (blooms) in those months.Components of micro- and nannoplankton — Theorganisms listed below were largely common toboth micro- and nannoplankton. If they weresmall in size, they contributed profusely to the9 nannoplankton and when large they were retainedby the net as microplankton.Skeletonema costatum, Thalassiosira sp., Naviculasp., Nitzschia closterium, Ceratulina sp., Fragilariaoceanica, Synedra sp., Dity/ion sp., Rhizosokniasp., Corethron sp., Gyrosigma sp., Pleurosigmasp., Chaetoceros sp., Asterionella japonica, Thalas-sioneina nitzschoides, Coscinodiscus sp., Surirella sp.,Biddulphia sp., Chlorella sp., Ankistrodesmus sp.,Scenedesmus sp., Pandorina sp., Eudorina sp.,Oadogoniumt sp. (last 3 occurred as microplanktononly)„Synechococctis sp., Merismopedia sp., Oscilla-toria sp., Peridiniunt sp., Gymonodiniam sp., andCeratium sp.From the above list it is clear that under bothgroups, the main constituents of the algae werediatoms. The organisms which formed blooms(constituting 50% or more of the total algal counts)were: Skeletonema costatum from January to Julyand October to December; Ceratulina sp., in June;and Merismopedia sp. in August, September andNovember.Seasonal variations in the rate of photosynthesis,chi. a concentration and cell numbers of differentsize groups are shown in Fig. 2. All the three pro-perties indicate that the contribution of smallestorganisms (less than 64 ,,J.in) remains large practicallythroughout the year. However, there was neitherany uniformity in the seasonal abundance of anyone particular size group of organisms nor was anyclearly marked rhythm in the properties. It seemsthat the larger organisms need rot have correspond-ingly higher photosynthetic rate or chlorophyllcontent as compared to smaller forms. Similarly,the high counts of smaller forms may not necessarilybe associated with high values of photosynthesisor chlorophyll.----0 NON-FRACTIONATED•—• FRAC T ION ATE DcFig. 1— Seasonal cycles of (a) photosynthesis (b) chlorophyll aand (c) cell numbers, shown by non-fractionated samplesand pooled values of fractionated samples taken from theCochin BackwaterResultsSeasonal cycle of production — Fig. 1 gives photo-synthesis, chi. a concentrations and . total cellnumbers for 1 year. The values for each fortnightwere averaged_ The figure includes two sets ofdata — one from non-fractionated samples and theother from integrated values of four fractionated• samples. For photosynthesis the two sets of valuesagreed very closely (Fig. la). The daily productionranged from a minimum of 4 mgC rn-3 d -1 in Julyto a maximum of 1500 mgC d-1 in December.The seasonal cycle obtained in the present studywas quite different from that reported earlier forthe period August 1965 to july 1966 12, indicatingthat there is no regular seasonal trend. Here also,brief pulses of high production were observed inMarch, November and December. Apart from thelowest values recorded in July and August, and thehighest values in November and December, therate of photosynthesis ranged between 100 and 200mgC M-3 d -1.147PHOTOSYNTHESIS CHLOROPHYLL403020102010Lit3020Iii10604020J FMAMJJASOND J FMAMJ J FMAMJJASONDCELL NUMBERSINDIAN J. MAR. SCI., VOL. 3, DECEMBER 1974Fig. 2 - Relative proportion of photosynthesis, chlorophyll a and cell numbers contributed by the algae of different size-groups from the Cochin Backwater (a) larger than 99 tan, (b) larger than 76 p.m, (c) larger than 64 tun, and (d) smallerthan 64 tkmTABLE 1 - PHOTOSYNTHESIS, CHLOROPHYLL AND CELL NUMBERS OF MICROPLANETON AND NANNOPLANKTON, EXPRESSED ASPERCENTAGES OF THE Two COMBINED IN EACH MONTH TOGETHER WITH RATIOS BETWEEN MICRO- AND NANNOPLANKTONMonths Photosynthesis Chlorophyll a Cell numbersMicro Nanno%Micro:nannoMicro%Nanno%Micro:nannoMicro%Nanno%Micro:nannoJan. 21.18 78.82 0-27 32.91 67.09 049 22.66 77.34 0.29Feb. 3-69 96.31 0-04 4355 5645 0.77 30-73 69.27 0-44March 9.42 90.58 0.11 43.97 56.03 0.78 32-04 67.96 048April 40.50 59.50 0.68 26.73 73.27 0.36 24-19 75-81 0.32May 16-47 83.53 0-19 15.41 84.59 0.18 29.36 70.64 0.41June 4F92 58-08 0.72 30.36 69.64 0.55 46.45 53.55 0.99July 34.41 65.59 0.52 44.66 55.34 0.80 75.23 24.77 3.03Aug. 22.21 77.79 0.38 31.18 68.82 0.45 12.55 87.45 0.14Sep. 13-65 86.35 0.15 37.24 62.76 0.59 73.92 24.08 3.15Oct. 34.71 65-29 0.53 22.20 77.80 0.28 57.10 42.90 1.33Nov. 55-44 44-56 1.24 39.50 60.50 0.65 71.41 28.58 2.45Dec. 12-77 87.23 0.14 14.27 85.73 0-16 4-20 95.80 0.04Average 25.53 74.47 31.83 - 68.17 40.15 59-85148QASIM et al.: MICRO- & NANNOPLANKTON IN WATERS OF TROPICAL ESTUARYTable 1 gives the relativeproportions of photo-synthesis, chlorophyll and cell numbers contributedby micro and nannoplankton during the year.Photosynthesis of microplankton ranged from 4to 55% and that of nannoplankton from 45 to96%. The ratio, micro: nanno, was less than 1throughout the year, except in November (Table1). Similarly, the quantity of chl. a in microplank-ton ranged from 14 to 45%. In contrast to this,the range in chl. a content of nannoplankton wasfrom 56 to 86% and the ratio between chlorophyllof micro to nannoplankton was less than 1 in allthe months. The range in the percentage of cellnumbers of microplankton was somewhat greater,from' 4 to 76%, and that of nannoplankton from24 to 96%. The ratio between the cell numberof micro to nannoplankton was greater than 1 inJuly, Septei-nber, October and November (monsoonand post-monsoon months), when larger organismsseem to be more abundant. This, however, is notreflected either from their photosynthesis or fromtheir chlorophyll, which once again indicates thatthe size of the organisms has little relation with theirphotosynthesis or chlorophyll.The average annual contribution of the threeproperties of micro and nannoplankton is given inTable 1. Although in all these properties the con-tribution of nannoplankton was significantly high,the difference was most marked in the photosyn-thesis of the two categories and least in their cellnumbers (Table 1). Probably, photosynthesis isthe best single property for evaluating the charac-teristic of the algae.DiscussionIn the present communication, the importanceof nannoplankton in tropical estuarine waters hasbeen shown, taking into account the algae measuring20 1.t.m and larger in size. These were predominantlydiatoms and this feature supports the view expressedby Yentsch and Rythers that diatoms constitute acrop many times greater than that of the flagellates.However, no estimate of organisms smaller than20 has been made except only in exceptional ca-ses, because of considerable difficulties encounteredin identifying them in preserved samples. From apreliminary examination, however, of some of thesmaller algae which are probably autotrophic flagel-lates, it is evident that their contribution may hefar greater than diatoms. Knight-jones' 7 hascollectively called these ultraplankton ' and hasemphasized their importance in phytoplanktonecology. Thus, the bulk of organic production inthe sea seems to be largely due to the activities ofautotrophic flagellates and this supports the viewexpressed by earlier workers2as.The broad distinction of planktonic algae intomicro and nanno, which the phytoplankton ecolo-gists have made on the basis of their size must in-clude ultraplankton so as to make the division morerealistic. In the English Charnel, Harvey19 foundthat the contribution of ultraplankton• (flagellates)was many times greater than other algae. Similarly,other reportsw ,23 have shown a far greater predo-minance of microflagellates as compared to diatoms.There is an overwhelming evidence to suggestthat practically in all types of environments,organisms of the nannoplankton and ultraplanktoncategories (smaller than 50 (t.m), dominate theprimary producers24 . This is because the smallcells have a faster rate of growth than that of thelarger forms 25 . The nannoplankton organisms, be-cause -of their small surface area, have a distinctadvantage over the microplankton in the utilizationof light and nutrients 26 , particularly in turbidwaters where the euphotic zone is shallow andnutrients are abundant. The small forms tend tosink far more slowly than the larger forms andhence they. continue to remain in the favourablezone of illumination for a longer time.Production of a large quantity of ranr oplanktonin the sea is ecologically important as planktotrophiclarvae will have to filter a smaller quantity ofwater to obtain the required amount of food_Probably for this reason, in tropical waters, a highproportion of benthic invertebrates produce plank-totrophic larvae (80-85%). This is in contrast toarctic and temperate regions, where, the productionof filter-feedirg stages by berthic animals is 5 and55-65% respectively 27 . Evidently, a filter-feederwould find it easier to remove from the environ-ment a smaller cell than a larger ore.References1. MALONE, T. C., Fishery Bull., 69 (1971a), 799.2. ATKINS, W. R. S., Nature, Lond., 156 (1945), 446.3. YENTSCH, C. S. & RYTHER, J. H., J. Cons. int. Explor.Mer, 24 (1959), 231.4. ANDERSON, G. C., Limnol. Oceanogr., 10 (1965), 477.5. MALONE, T. C., Limnol. Oceanogr., 16 (1971b), 633.6. GILMARTIN, M., J. Fish. Res. Bd Can., 21 (1964). 505.7. TEIXEIRA, C., Bol. Inst. Oceanogr. Universidade de SaoPaulo, 13 (1963), 53.8. RODHE, W., VOLLENWEIDER, R. A. & NAUWERCK, A.,in Perspectives in marine biology, edited by A. Buzzati-Traverso (University of California Press, Berkeley andLos Angeles), 1958, 299.9. GOLDMAN, C. R. & \%ETZEL, R. G., Ecology, 44 (1963), 283.10. KALFF, J. Limnol. Oceanogr., 17 (1972), 712.11. RYTHER, j. H., Biol. Bull. Woods Hole, 106 (1954), 198.12. QASIM, S. Z., WELLERSHAUS, S., BHATTATHIRI, P. M. A.ABIDI, S. A. H., Proc. Indian Acad. Sci., 69 (1969), 51.13. QASIM, S. Z., BHATTATHIRI, P. M. A. & DEVASSY, V. P.,Mar. Biol., 12 (1972), 200.14. QASIM, S. Z., BHATTATIHRI, P. M. A. & DEVASSY, V. P.,Mar. Biol., 21 (1973), 299.15. WYATT, T. & QASIM, S. Z., Limnol. Oceanogr., 18 (1973),301.16. UNESCO, Monographs on oceanographic methodology, 1.(1966), 1.17. KNIGHT-JONES, E. W., J. Cons. perm. Mt. Explor. Mer,17 (1951), 140.18. KNIGHT-JONES, E. W. & WALNE, P. R., Nature, Land.,167 (1951), 455.19. HARVEY, H. W., J. mar. biol. Ass. UK, 29 (1950), 97.20. BERNARD, F., Deep Sea Res., 1 (1953), 34.21. MCALLISTER, C. D., PARSONS, T. R. & STRICKLAND,J. D. H., J. Cons. Perm. int. Explor. Mer., 25 (1960),240.22. RILEY, G. A., Limonol. Oceanogr., 2 (1957), 252.23. BAsHARAH, L., Bull. Mar. Sci. Gulf Carrih., 7 (1957), 201.24. RAN-mom. , J. E. G., in Advances in ecological research,edited by J. B. Cragg (Academic Press, London andNew York), 3 (1966), 117.25. EPPLEY, R. W., ROGERS, J. N. & MCCARTHY, J. J.,Limnol. Oceanogr., 14 (1969), 912.26. MuNE., W. H. & RILEY, G. A., J. Mar. Res., 11 (1952), 215-27: THORSON, G., Biol. Rev., 25 (1950), 1.149,

Contribution of microplankton and nannoplankton in the waters of a tropical estuary

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Contribution of microplankton and nannoplankton in the waters of a tropical estuary

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