Biochemical composition of zooplankton from Visakhapatnam harbour waters, east coast of India

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1 Indian Journal of Marine Sciences Vol. 31(2), June 2002, pp Biochemical composition of zooplankton from Visakhapatnam harbour waters, east coast of India *I. Nageswara Rao & R. Ratna Kumari Marine Chemistry Laboratory, School of Chemistry, Andhra University, Visakhapatnam , A.P, India [ *inageswararao@yahoo.com ] Received 18 May 2001; revised 28 January 2002 Proximate composition, zooplankton biomass, protein, lipid, carbohydrate, organic carbon and calorific content of mixed zooplankton in the Visakhapatnam harbour waters were estimated. Biomass varied from 15.2 to 74.0 ml.100 m -3 ( x =31.05 ±17.7) in the outer harbour and 10 to 64.0 ml.100 m 3 ( x =26.30±14.8) in the inner harbour. Copepods, tintinnids, decapods and ognaths formed dominant groups of total zooplankton ( > 90%) in the harbour waters throughout the year. Of the biochemical fractions of zooplankton, protein formed the major component, varied from to 563 mg.g -1 ( x =379.62±107), lipid varied from 61.2 to 181 mg.g -1 (x =103±32.7). Carbohydrate ranged from 65.5 to mg.g -1 ( x =85.78±16.92), organic carbon varied from to mg.g -1 (x =380.44±33.6) and calorific values varied from 2.2 to 5.4 ( x =3.5±.94) k.cal.g -1. Higher values of these constituents were observed during high saline premonsoon and postmonsoon periods when the population densities of copepods, tintinnids, decapods, ognaths were high. Significant positive correlations (P < 0.01) observed between calorific values, protein, lipid indicates to certain extent, that latter act as metabolic reserve of the zooplankton. Based on the results zooplankton do not have extensive lipid storage suggesting that protein in addition to the lipid may serve as metabolic reserve. Relatively higher calorific values were attributed to the dominance of copepods in the zooplankton population throughout the year. [ Key words : Zooplankton, biomass, biochemical composition, Visakhapatnam harbour ] Studies on the biochemical composition and energy content of zooplankton is important to have a better understanding of organic production, productivity and cycling of biogeochemical elements in the marine environment. Such information is of much importance in estimating the energy available to higher trophic levels, which in turn, can be used to estimate harvestable fishery resources. Much of the available information pertaining to biochemical composition and nutritive value of zooplankton is from estuarine, coastal, inshore and offshore waters of India 1-6. However, information on the seasonal variation in biochemical composition of zooplankton from eutrophic regions along the east coast of India is not available. The present study deals with the annual variations in biomass, biochemical composition, organic carbon and calorific content of mixed zooplankton collected from the Visakhapatnam harbour waters. Materials and Methods Visakhapatnam harbour, located on the east coast of India (17 o N and 83 o E) extends 5 km from the northwestern arm to the outer harbour and is connected to open sea through the entrance channel. Tides are chiefly semi-diurnal and have a mean range of 1.2 m. Considerable fresh water influx into the harbour occurs through a monsoon-fed stream Megadrigedda, particularly during monsoon season. It is also the principal source of industrial effluents (petroleum products, fertilizers, polymers, zinc-lead wastes etc.,) into the inner harbour, since this stream is used as a conduit for the discharge of all the industrial wastes. An appreciable amount of untreated domestic sewage is empted partly into northern arm and mainly into the sewage channel in the harbour adding to the organic load. Pollution studies in the harbour waters were carried out since 1970 s. High inorganic nutrients (nitrate , ammonia , phosphate , and silicate ppm) and organic loads were reported in the harbour waters 7,8 Surface zooplankton samples were collected at monthly intervals from March 1995 to February 1996 in three stations at inner harbour (st.1 st.3) and one station (st.4) in outer harbour (Fig. 1) through horizontal hauls using a HT net (mouth area 0.25 m 2 ; 200 μm mesh size) with a calibrated flow meter fixed at the

2 126 Indian J. Mar. Sci., Vol. 31, No. 2, June 2002 center point of the net mouth. After measuring the biomass (displacement volume) samples were immediately washed with distilled water. One half of each sample was preserved for taxonomical studies and the other half was freeze dried. The freeze-dried samples Fig. 1 Station locations were again dried at 50 o C until constant weight was obtained. The dried samples were used for estimation of protein 9, lipid 10, carbohydrate 11, and organic carbon 12. Calorific content was estimated using the conversion factors of, 5.7, 9.3 and 4 k.cal.gr -1 respectively, for protein, lipid and carbohydrate 13. Results and Discussion Biomass, dry weight and population density Zooplankton biomass, dry weight and total population densities in the harbour waters are given in the Table 1. Biomass and dry weight in the outer harbour varied from 15.2 to 74.0 ml.100 m -3 (x =31.1±17.7) and 1.78 to 7.79 g.100 m -3 (x =3.7±2.1). In the inner harbour they ranged from 10.0 to 64.0 ml.100 m -3 ( x =26.2±14.8) and 1.62 to 6.82 g.100 m -3 ( x =3.4±1.7). Total zooplankton population in the respective harbour waters varied from to no.100 m -3 (x =389157±269921) and to no.100 m -3 (x =267920±242074). Higher biomass, dry weight and population densities observed Table 1 Monthly variation in biomass, total population and dominant groups of zooplankton in the Visakhapatnam harbour waters Months Outer Harbour Inner Harbour Biomass (ml.100 m -3 ) Dry weight (gr.100 m -3 ) Dominant groups Biomass (ml.100 m -3 ) Dry weight (gr.100 m -3 ) Total population (no. 100 m -3 ) Total population (no. 100 m -3 ) Dominant groups March Cope, tin, deca, Apil Tin, cope, deca, May Cope, deca, tin, June Cope, tin, deca, July Cope, deca, tin, cheat Aug Cope, deca, tin, Sep Cope, tin, deca, oiko Oct Cope, tin, deca, Nov Cope, deca, tin, sipho Dec Cope, tin, deca, Jan Cope, tin, deca, Feb Cope, tin, deca, Tin, cope, deca, Cope, tin, deca, Tin, cope, deca, Cope, tin, deca, Cope, tin, deca, Cope, deca, tin Cope, tin, deca, Cope, deca, tin, oiko Cope, deca, tin, Cope, tin, deca, Cope, tin, deca, Tin, cope, deca, Tin = Tintinnids; Cope = Copepods, Deca = Decapods, Chaet = Chaetogaths, Oiko = Oikopleura, - fish eggs/larvae; Sipho = Siphonophores, Bival = Bivalves

3 Nageswara Rao & Ratna Kumari : Biochemical composition of zooplankton 127 during high saline premonsoon (March to May) and postmonsoon (December to February) periods (Table 1) were attributed to high number of zooplankton are associated with high productivity during these periods due to the stable conditions prevailed in the harbour waters. Low values of these were observed during monsoon season (June to November) probably attributed to the low saline and high turbid nature of these waters when the productivity and zooplankton densities are usually low The present values are comparable with the values reported from the offshore 17 and harbour waters 18 of Bombay; northern part of central Arabian Sea 3 ; Bombay High (oil platform) area in the Arabian Sea 5 and from the waters of Bay of Bengal 4. Twenty zooplankton groups were identified in harbour waters throughout the study period and total number of populations were always higher in outer harbour than in the inner harbour waters due to the higher degree of pollution in the later. Copepods contributed maximum (with a mean of 68.86, %) followed by tintinnids (19.1, %), decapods (7.04, 5.42 %), molluscans (1.78, 2.09 %), ognaths (1.24, 0.48 %), coelenterates (0.6, 0.29 %), fish eggs and larvae (0.49, 0.53 %), adult crustaceans (0.3, 0.26%), tunicates (0.3, 0.18%) and miscellaneous groups (0.28, 0.47%) including polyes, nematodes, worms and turbellarians in the respective harbour waters. Biochemical components Monthly variations of protein, lipid, carbohydrate, organic carbon and calorific values in the mixed zooplankton of the harbour waters are given in Fig. 2. Protein formed the major biochemical component and ranged from to 563 mg.g -1 ( x =393.6±111.5) in the outer harbour and to mg.g -1 ( x =366±100.2) in the inner harbour waters. Protein values observed in the present study are comparable to the values earlier reported for the west coast of India 1, northeastern Arabian Sea 2, northwest Bay of Bengal 6 but higher than those of northern part of central Arabian Sea 3, Bombay High (oil platform) are in the Arabian Sea 5. Protein values were high when higher number of copepods, tintinnids, decapods, ognaths, ves, oikopleura, siphonophores of total zooplankton populations are associated with high productivity of the harbour waters in the premonsoon (March-May) and postmonsoon (Dec.-Feb.). Compared to carbohydrate and lipid (Fig. 2), protein formed the major fraction, indicating the usefulness as energy reserve 19. Zooplankton utilizes the protein as an additional source of energy at times of stress 20. The lipid content in the present study showed wide variations from 67 to 181 mg.g -1 (x =107.3±32.5) in the outer harbour and 61.2 to mg.g -1 ( x =98.4±32.2) in inner harbour. The values recorded in the present study agree with the values reported earlier 1,6 but are lower than those reported for zooplankton from northern part of central Arabian Sea 3 and Bay of Bengal 4. The lipid content is more in zooplankton collected during premonsoon and postmonsoon periods due to the occurrence of high lipid containing groups like copepods, tintinnids, decapods, ognaths and fish eggs and larvae. However, lipid values observed in the present study are lower when compared to earlier values reported from higher latitudes 21, which may be attributed to the availability of food throughout the year 22. Seasonal fluctuations in lipid were attributed to their storage and utilization during starved period when it serves as an effective energy reserve. The values of carbohydrates in the present study are relatively high, ranging from 70.3 to mg.g -1 ( x =91.4±18.9) in the outer harbur and 65.5 to mg.g -1 (x =80.12±12.35) in the inner harbour, which is in agreement with reported values of Indian Fig. 2 Monthly variations of biochemical constituents, organic carbon and calorific values of zooplankton from Visakhapatnam harbour during March 1995 to February 1996

4 128 Indian J. Mar. Sci., Vol. 31, No. 2, June 2002 waters 2,3. Carbohydrate content in zooplankton depends upon its composition, decreasing with increase of gelatinous organisms and increasing with copepod populations. In the present study, copepods are dominant throughout the year. This together with its seasonal occurrence of phytoplankton blooms in the harbour waters 23 may be responsible for higher carbohydrate content. The highest values observed in March May, January - February might be due to the larger quantities of phytoplankton which could not be separated from the zooplankton samples. Low carbohydrate content during the rest of the months reflect the short-term variation in glycogen storage of the marine organisms which in turn, depends upon their feeding activities. Based on the above observations, we are of the opinion that although lipid and carbohydrate could function as important food reserve, protein may also be utilized and function as a reserve food 19,20. Studies on the mysid Neomysis interger 24 indicate that on starvation amino acids from protein appear to be mobilized and subsequently deaminated with a rapid rise in ammonia excretion. Loss of protein in zooplankton during starved condition indicating its utilisation has been well documented 20. Mobilisation of protein for metabolic requirements is believed to be essential in tropical zooplankton where lipid reserves are low, as has been shown by earlier observation in zooplankton off the Indian coasts 1-3,6. Organic carbon of zooplankton is a reliable source of energy equivalent of secondary production for any season 25. It is mainly dependent upon the species composition, the size of the different populations, and availability of food in general and physiological state of the individual organism 26. In the present study, the values varied from to ( x =398.2±28.5) in the outer harbour and 335 to 435 mg.g -1 ( x =362.7±28.7) in the inner harbour with peak values during March to May and January to February coinciding with high population densities of copepods, tintinnids, decapods and ognaths. These values, however, are higher than those reported earlier for zooplankton of Arabian Sea 3 and Bay of Bengal 4. Calorific value The calorific values observed in the present study ranged from 2.3 to 5.4 kcal.g -1 (x =3.5±1.1) in the outer harbour and 2.2 to 5.1 ( x =3.3±0.9) kcal.g -1 in the inner harbour waters. The mean values observed in the present study are comparable to those reported for the Arabian Sea 2 and Bay of Bengal 4,6. Differences in calorific values in the harbour zooplankton may be attributed to the species composition, time of collection and physiological state of zooplankton. High calorific values in the present study were associated with zooplankton dominated by copepods, tintinnids, decapods, and ognaths in the total zooplankton. Biomass significantly correlated with copepods (r=0.8) in harbour waters. However, it significantly correlated with ognaths (r=0.86), coelenterates (r=0.70) and fish eggs and larvae (r=0.74) are only significant in the outer harbour, and tintinnids Table 2 Correlation matrix of total population, biomass, dry weight and biochemical constituents of zooplankton in the Visakhapatnam harbour water Outer Harbour TP DV DW OC CHO PRT LP CV TP DV * 0.61* 0.70 DW OC CHO * PRT LP * CV Inner Harbour TP : Total population CHO : Carbohydrate DV : Displacement volume PRT : Protein DW : Dry weight LP : Lipid OC : Organic carbon CV : Calorific value * P < 0.05

5 Nageswara Rao & Ratna Kumari : Biochemical composition of zooplankton 129 (r=0.84), adult crustaceans (r=0.84) decapods (r=0.64) and molluscans (r=0.70) in the inner harbour. Protein was significantly correlated with copepods (r=0.87, 0.84), tintinnids (r=0.62, 0.74), decapods (r=0.74, 0.75) and coelenterates (r=0.74, 0.70) in both inner and outer harbour waters, indicating that major fractions of biochemical components are derived from these groups of zooplankton. Biomass, dry weight, total population, biochemical components and calorific values (Table 2) indicate significant positive (P <0.01) correlations among them in both outer and inner harbour waters implying that biochemical components play an important role in energy metabolism. It is therefore evident from the present study that variations in biochemical constituents are influenced by the species composition of zooplankton. Protein formed a major component and may serve as the main metabolic reserve as reported from other areas. The zooplankton of the harbour waters do not appear to have an extensive storage of lipid and carbohydrate and this might be due to availability of phytoplankton food throughout the year 23. Higher calorific values observed in the present study may be attributed to the dominance of copepods in the total zooplankton throughout the study period. Acknowledgement The authors are grateful to the Department of Ocean Development, New Delhi for providing research grant. References 1 Goswami S C, Rao T S S & Matondkar S G P, Biochemical studies on some zooplankton off the west cost of India, Mahasagar-Bull Natn Inst Oceanoagr, 14 (1981) Sumitra-Vijayaraghavan, Selvakumar R A & Rao T S S, Studies on zooplankton from the Arabian Sea off the South Central West Coast of India, Indian J Mar Sci, 11 (1982) Nandakumar K, Bhat L K & Wagh A B, Biochemical composition and calorific value off zooplankton from Northern part of Central Arabian Sea, Indian J Mar Sci, 17 (1988) Sreepada R A, Rivonkar C U & Parulekar A H, Biochemical composition and caloric potential of zooplankton from Bay of Bengal, Indian J Mar Sci, 21 (1992) Bhat K L & Wagh A B, Biochemical composition of zooplankton of Bombay High (oil platform) area in the Arabian Sea, Indian J Mar Sci, 21 (1992) Krishna Kumari L & Goswami S C, Biomass and biochemical composition of zooplankton from Northwest Bay of Bengal during January 1990, Indian J Mar Sci, 22 (1993) Satyanarayana D, Sahu S D & Panigrahy P K, Assessment of eutrophication in the marine environment of Visakhapatnam using nutrient index as a tool, Indian J Mar Sci, 21 (1992) Raman A V, Pollution effects in Visakhapatnam harbour, India : An overview of 23 years of investigations and monitoring, Helgolander Meeresunters, 49 (1995) Lowry O H, Rogenberg N J, Fare A L & Randall R J, Protein measurement with Folin-phenol reagent, J Biol Chem, 193 (1951) Folch J, Lees M & Stanley G H S, A simple method for the isolation and purification of total lipids from the animal tissues, J Biol Chem, 226 (1957) Dubios M, Gillas K A, Homillon J K, Rebus R A & Smith F, Calorimetric method for determination of sugars and related substances, Anal Chem, 28 (1956) El Wakeel S K & Riley J P, The determination of organic carbon in marine muds, J Cons Perm Inst Explor Mer, 22 (1957) Winberg G G, Determination of calorific value of sample from its chemical composition, in Methods for the estimation of production of aquatic animals, edited by G G Winberg (Academic Press, London) 1971, pp Madhupratap M & Haridas P, Composition and variation in the abundance of zooplankton of back waters from Cochin to Alleppy, Indian J Mar Sci, 4 (1975) Selvakumar R A, Nair V R & Madhupratap M, Seasonal variations in secondary production of the Mandovi-Zuari estuarine systems of Goa, Indian J Mar Sci, 9 (1980) Nair V R, Gajbhiye S N, Ram J M & Desai B N, Biomass and composition of zooplankton in Auranga, Ambika, Purna and Mindola estuaries of South Gujarat, Indian J Mar Sci, 10 (1981) Nair V R, Peter G & Paulinose V T, Zooplankton studies in the Indian Ocean II. 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