Xcta hydrochim. e t hydrobiol. 13 (1985) 2, 117-221

S. RARKAR and B. B. JAXA

Department of Zoology. University of Kalyani, Kalyani West Bengal, India

Biomass Determination in Some Species Using a Geometric Equivalent Technique of Plankton Organisms

ASuvininry: The plankton collected from three fish ponds shows a considerable variability s ithin a pond, betneen the ponds and in the coiirse of the year. The individual rolumes or weights are (minimum -mean - maximum) : Gleotrichia. echinulata 41--252-879 ~ g 3 , Chlorella vzdgaris 18-42- 94 pniJ, Oscillatorin arnphigranulata 99-306-827ym3, Bmchionus plicntilis 1-4.9-18 pg, nacplia 0.5-1 25-2.36 pg, JIesocyclops hynlinus 4-45-369-yg, Heliodinptorwus i r i d u t i s 41-202-288 yg, Daphnia mrinata 186-1468-4578 pg.

Introduction

While the enurneration of planktonic organisms per unit volume of water indicates the quantitative abundance of the organisms, numbers do not give a true evaluation of the actual biomass because organisms occurring in water bodies often differ greatly in size. Moreover, even if the weight of larger organisms is equal to the weight of smal- ler ones in an ecosystem, the number of smaller organisms would be vastly greater than that of the larger ones. Therefore, the number of individuals of each species is expressed by the volume per unit volume of water. I n general, a biomass pyramid gives a rough picture of the overall effect of the food chain relationship for the ecolo- gical group as a whole (ODUM).

I n the ecosystem analysis, the biomass determination of plankton involves an elaborate technique. For this reason, there has been a number of attempts to provide a list of cell volumes for the species of phytoplankton found in temperate bodies of water (NAUW-ERCK; PAASCIIE; WETZEL; VOLLENWEIDER). However, there is no such information in tropical water bodies. The purpose of this inveetigation was to pre- pare a list of approximate weights of plankters most abundant) in the fish ponds of West Bengal. The data can be profitably utilized in computing their biomass from the enumeration of plankton, which is often done in the ecosystem analysis.

Materials and Methods

Surface plankters were collected from three fish farming ponds located at Kalyani, West Bengal, during September 1979 to April 1980. The collection was made by a standard plankton net (No. 21 with 77 meshes per cm). The volume of freshly collect- ed plankters was determined using their geometric equivalent technique. The mean 15.

218 SARKAR, S., JAN-%, B. B.: Biomass of Plankton Organisms

dimensions of the cells were computed i n a microscope assuming that their form corre- sponds roughly to simple geometric solids (WLNBERG). The mean cell volume of each species was based on the examination of fifteen to twenty individualsfrom each sample. From the collected samples, several plankton organisms were selected for the volume determination because they frequently occur in West Bengal ponds. The volume of C'hlorelln and Cleotrichirt (Fig. 1 ) was measured by considering their shape as spheres and that of Oscillcrtorirc a n d Brachionus (Fig. 1) as cylinders. The main bodies of Musocyclops, Heliodiccptontus, Dwphiiia and naupliiis (Fig. 1) were considered as cyl-

Chiore i io vulgaris Brachionus p i icat i l is Naup i ius l a r v a Heiiodiaptornus viduus

I 1 I 1

I I

I I

I I I-- Cylinder - Cylinder I ! I i I i I 1

I I

I I

J I

Dsc i l lo to r io Gieo tr ichio Mesocyclops hyolinus Dophnio car inoto omphigranulafo echinuloto

Fig. 1. Species of phyto- and zooplankton selected for the volume determination Abb. 1. Fur die Volrimenbestimmung gewlihlte Spezies von Phyto- und Zooplanktoc

inders and their antennae as cones. The following geometric formula was used for the volume determination

(1) Splierc = (4 t.Jn)/3

( 3 ) Cone = (,.?Ch) '3 (2) C'ylinder =r%h

From the calculated cell volnnie of the organisms their wet weight was estimated, as the specific gravity o f wet matter of the bod>. of aquatic organisnis is usually

Acta hydrochim. et hydrobiol. 13 (1985) 2 219

considered a s unity (WINBERG). The volume of phytoplankton was expressed as pm3, while the volnme of zooplankton in pm3 was divided by 1 0 6 in order to express their mass in pug.

Results and Discussion

The results of the volume determination of different taxa of phyto- and zooplank- ton are presented in Fig. 2 .

It was observed that each species of plankton showed large variations in their cell volume in different individuals. Also, the cell dimensions of each species differed from pond to pond as well as from one month to another in the same pond. The vol- lime of Chlorella wdyaris, as a whole, rangedfrorn 18 to 94 pm3 showing about a $fold individual variation, the mean volume obtained from each sample varied between 26 and 52 pm3 in different ponds. On a seasonal basis, the volume was relatively snialler (31 pm3) during January than in other months ( ~ 6 2 pm3).

The volume of Gleotrichicr varied between 41 and 879 pm3 exhibiting a more than 90-fold intraspecific variation, while the mean volume for each sample ranged from 90 to 347 pmJ in these ponds. The magnitude of the seasonal variation in the mean volume was a s much a s 2-fold in the pond 3.

There were about 8,fold variations from the minimal (99 pm3) to maximal (827 pm3) rolume of Oscillatoria aniphigranulata in these ponds. The seasonal fluctuation in the mean volume was maximum (193 to 414 pm3) and minimum (248 to 260 pm3) in the pond 1 and the pond 3, respectively.

Brachionus plicatilis also showed a large individual variation (20-fold) in their mass, which varied from 1 to 18 pg. The seasonal variations in the mean body weight were well pronounced in the pond 1 (=-5 fold), but less defined in the pond 2 ( < 2 fold).

Mesocyclops hyalinus was the most common among all the members of zooplank- ters. The range of variation in weight among the smaller ones was between4 and 115 yg, while the variation was between 23 and 369 pg among the larger ones. The overall seasonal variation in the average weight of Me5ocyclops hyulinus was between 11 and 210 pg showing nearly a 20-fold variation. The inean weight was relatively lower (13 to 23 pg) during September and higher (76 to 310 pg) during January.

There has been a more than 10-fold variation in the weight of Heliodirrptornus riduus in these fish ponds. The minimal weights ranged from 41 to 288 pg, while the iiiaxinial weights ranged from 155 to 448 pg. Helaodiaptonius occurring in the pond 3 was relatively higher in the mean weight (214 to 359 pg) than in other ponds.

The magnitude of weight differences in nauplius larvae was about 15-fold in these three fieh pond8. Nauplius larvae occurring in the pond 3 had relatively smaller average weights(0.5 to 1 pg), compared to meanweights inthepondl (1.13to 1.25 pg) and the pond 2 (2.35 pg).

Duphnia carinata, represented from the pond 1, showed a more than 25-fold variation in weight in different individuals. Cyclomorphosis in cladocerans has often caused large variations in their body size. The mean mass of Daphnicc uzrinata based on the examination of individuals from each sample ranged from 186 vg to 4578 pg. There

ass of Plankton Organisms

c d

B

._ D

.- u c

Acta liydroc him. e t hydrobiol. 13 (1953) 2 221

has been a %fold seasonal variation in the mean weight with a greatly reduced weight in January (870 pg) and a n increased weight (2416 pg) in December.

I t i s fairly evident from this s tudy that all species of plankton showed large intra- specific, interspecific, spatial and seasonal variations in their volume. This variation, being undoubtedly due to the nutrient dynamics of the ponds, is likely to greatly alter the quantum of plankton food to the fish population, and the enumeration of plankton does not always give a t rue evaluation of the system as there are large var- iations i n the size of plankters.

The intraspecific variation of the volume appeared to be maximum i n Gleotrichitc ranging from 41 to 879 pm3 (21-fold) and minimnm in Chlorellcc ziulyaris (18 to 94 p113).

The overall mean volume of three taxa of phytoplankton varied in the order: Chlorelltr (42 pmJ) -= Gleotrichiu (252 pms) -= Oscillatoritc (306 pm I ) . NAUWERCK and WETZEL, however, have reported larger sizedOscillatoria of 1 mm height (0. limnetim 17,500 pm3; 0. rubescem 30,000 pml) and Chlorella vulyaris (200 pmn) from temperate lakes.

The intraspecific variation in Mesocyclops was extremely high ( =- 100 times) among all zooplankters examined. The average weight of nauplius (1.25 pg) was the lowest, while that of DapAnin (1468 pg) was the highest of all. The mean weight of Helio- diaptomus with their large antennae (202 pg) was as much as 6 times higher than that of Mesocyclops (45 pg). Since there was a large intraspecific and interspecific variation in the size of plankters, ~'OLLENWEInER suggested that the cell volume of important forms should be determined in every particular case by using freshly collected samples, as shrinkage and cell deformation may occur in fixed materials.

References

SAUWERCK, A. : Die Beziehungen znischen Zooplankton und Phytoplankton im See Erken

OUUM, E. P.: Fundamentals of ecology. Philadelphia, Pa. W. B. Saunders Co., 1971. PAASCHE, E. : On the relationship between primary production and standing stock of phytoplank-

ton. J. Cons. Int. Explor. Mer. 2 (1960), 33-48. VOLLENWEIDER, R. 8.: A manual on methods for measuring primary production in aquatic

environments. Oxford, Blackwell Scientific Publications, I B P Hand Book No. 12, 1974. WETZEL, R. W. : Limnology. Philadelphia, Pa. W. B. Saunders Co., 1975. WINEERG, G. G. : Methods for the estimation of production of aquatic animals. London, Academic

Symb. Bot. Uppsal. 17 (1963), 1-163.

Press, 1971.

Mnnzrskripteingang: 4. 2. 1984.

Anschrift des vernntzi,ol-tlichen Verfassers:

Dr. B. B. JAN-%, Vniveraity of Kalyany, Department of Zoology. IXD - 741235 Ka lpny (TI'. B.).