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Indian J. Fish., 49(3) : 267-273, Jul.-Sep., 2002

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Distribution of phytoplankton pigments in the Nethravathi estuary G. GOWDA, T.R.C. GUPTA, K.M. RAJESH, H. GOWDA*, C. LINGADHAL AND A.M. RAMESH Department of Fisheries Environment and Ecology College of fisheries, Mangalore - 575 002, India * Department of Karnataka State Remote Sensing Application, Bangalore

ABSTRACT Distribution of phytoplankton pigments were studied during Feb. 1993 - May 1994 in the Nethravathi estuary, Mangalore. Chlorophyll a, b and c varied between 1.18 - 11.35 mg/m3, 0.12 - 14.88 mg/m3 and 0.08 - 25.82 mg/m3 respectively with higher concentrations during May, June - July and Nov. - Dec. The carotenoids varied between 0.01 and 16.31 mg/m3 with peaks during Oct. - Nov. and March - April. Variation of pigments are due to temperature, salinity and nutrients in the Nethravathi estuary.

Introduction Photosynthetic pigments are widely used to predict the phytoplankton standing crop (Fogg, 1975), as pigments are more specific to plants and easy to estimate (Moss, 1967). Chlorophyll a is an index of primary production which is used for estimating the living resources of aquatic ecosystems, whereas, the degradation products (chlorophyll b and c, phaeophytin and phaeophorbide a) are diagnostic indicators of physiological status, detrital content and grazing levels in natural populations of phytoplankton. The ratios of chlorophyll a/c could vary significantly due to species composition (Law and Wong, 1978), nutrient and illumination temperature and salinity (Sournia, 1978). Carotenoid also serve as indicators of standing crop (Lehman, 1981). Seasonal distribution of chlorophyll pigments, carotenoids and the

abundance of phytoplankton with environmental factors help to understand the biological processes occurring in the ecosystem. Seasonal variations of phytoplankton pigments are available for different estuaries and coastal waters of India (Balasubramanian, 1974; Bhargava and Dwivedi, 1974; Bhattathiri and Devassy, 1977; Ram et al., 1984; Desai et al., 1984; Balachandran et al., 1989, Akpen and Offen, 1993 and Satyanarayana et al., 1994). Since information on phytoplankton pigments is lacking in Nethravathi estuary, the present study was initiated to understand the variation of pigments in this estuary.

Materials and methods The study was carried out in the Nethravathi estuary (12° 50' N and 74° 50' E) for 16 months during Feb. 1993 -

G. Gowda, et al. May 1994. Three stations were fixed in the lower estuary, St. 1 at bar mouth, St. 2 and 3 at 3 and 8 kms away from the bar mouth into the upper estuary (Fig. 1). Surface water samples were collected monthly by using a mechanised dinghy during high tide for pigment analysis. Samples were filtered through 300 µm mesh net to remove heterotrophs, then through 0.45 µm GF/C glass fibre filter under reduced pressure. Pigments were extracted from the filters using 90% acetone and analysed spectrophotometrically (Parsons et al., 1989). Phytoplankton samples were collected using Heron - Tranter net with a mesh size of 64 µm, preserved in 4% formalin and identified to species level using compound microscope. Water temperature, salinity and nutrients were estimated following standard methods (Strickland and Parsons, 1972; Parsons et al., 1989).

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Fig.1. Map showing the location of stations.

1973; Bhargava and Diwedi, 1976; Desai et. al., 1984; Nair, 1990). Chlorophyll c ranged from 0.08 to 25.82 mg/m3. Higher values were found during late postmonsoon period. The dominant peaks were observed during Nov. at St. 1 (19.44 mg/m3), St. 2 (14.37 mg/m3) and May

Results Pigments The biomass of chlorophyll a varied between 1.18 and 11.35 mg/m3 with three peaks. Higher values were observed during May, July and Nov. - Dec. Peaks were noticed during July (10.62 mg/m3) in the bar mouth region, May (10.25 mg/m3) in the middle and July (10.25 mg/m3) in upper stretch of the estuary. Pre and post monsoon peaks were common in other estuaries (Nair, 1990 and Vijayalakshmi, 1986). Chlorophyll b fluctuated between 0.12 and 14.88 mg/m3 with maximum during May, July and Nov. The dominant peaks were noticed during Nov. (14.88 mg/m3 and 7.58 mg/m3) at St. 1 and 2 respectively, whereas, at St. 3 dominant peak was noticed during July (4.85 mg/ m3). Higher chlorophyll b was observed during May, July and Oct. - Dec. along south west coast of India (Bhargava,

Fig.2. Distribution of chlorophyll pigments and phytoplankton biomass in Nethravathi estuary.

0.58 0.14 1.28 1.02 2.98 0.77 0.79 0.06 7.89 5.38 0.29 1.71 0.33 0.53 0.94 0.63 0.002 0.65 0.45 0.16 0.09 0.01 0.05 0.40 1.60 1.86 0.14 0.23 0.57 0.29 0.62 0.13 0.40 0.13 0.45 4.60 4.89 0.31 0.53 0.32 0.33 4.80 0.31 0.38 0.02 0.10 0.07 0.38 0.04 0.10 0.05 0.06 1.33 0.47 0.37 1.54 1.97 1.47 0.44 0.85 0.46 0.08 0.07 0.34 0.24 0.16 1.46 0.89 3.50 0.93 0.33 0.26 5.22 4.36 0.32 0.65 0.72 0.20 0.49 1.02 0.27 0.37 0.09 0.08 0.11 0.01 0.03 0.31 0.17 1.13 0.14 0.52 0.50 0.47 0.90 0.15 0.13 0.03 0.76 0.70 1.45 1.31 0.38 0.31 1.96 3.36 0.55 0.27 0.23 0.02 0.03 0.88 0.04 0.03 0.02 0.15 0.76 0.81 0.32 0.68 0.93 1.77 0.24 0.32 0.46 0.12 0.17 0.19 0.22 0.30 1.49 0.03 2.19 1.09 0.84 0.57 3.50 8.5 0.49 1.32 0.11 0.81 0.43 0.72 0.51 0.23 0.54 1.10 1.30 0.50 0.50 0.35 3.49 5.17 0.83 0.34 0.03 0.04 0.34 0.86 0.09 0.11 0.25 0.38 0.70 0.02 0.59 0.06 0.37 3.96 0.12 0.20 0.52 0.11 0.13 0.22 Feb, 1993 Mar. April May June July Aug. Sep. Oct. Nov. Dec. Jan, 1994 Feb. Mar. April May

0.03 0.04 0.23 0.15 0.07 0.01 0.02 0.34 0.71 4.34 0.14 0.38 0.49 0.37 0.50 0.31

c/a b/a Months

Station 1 Carotenoids/a

TABLE 1. Ratios of different pigments Station 2 Phaeopigment/a b/a c/a Carotenoids/a Phaeopigment/a

b/a

c/a

Station 3 Carotenoids/a

Phaeopigment/a

Phytoplankton pigments in the Nethravathi estuary

269 (25.82 mg/m3) in St. 3. Among the pigments, chlorophyll a values were generally higher than b. However, chlorophyll b and c were observed to vary conspicuously during late premonsoon and monsoon. The predominance of chlorophyll c was observed during postmonsoon and monsoon period in the estuaries along the west coast of India (Qasim and Gopinathan, 1969; Desai et al., 1984). The percentage composition of chlorophylls, carotenoids and phaeopigments are given in Fig. 3. Primary peak was noticed during May - June and secondary during Nov. - Dec. Chlorophyll values varied between 2.60 and 38.08 mg/ m3 in the estuaries of Goa (Bhargava and Dwivedi, 1976). Carotenoids showed maximum values varing between 0.01 and 16.31 mg/m3 during Oct. - Nov. and March - April. The peak values were noticed during Nov. at all stations; (16.31, 4.82 and 5.33 mg/m 3 at st. 1,2,3, respectively). Carotenoids were always found to be less than chlorophyll a. The concentration of phaeopigments were more during Oct. - Nov. and June - July with peak values in Nov. at all stations, ranging between 0.11 and 32.04 mg/m3. Ratios of pigments are presented in Table 1. Chlorophyll a/b was dominant during late monsoon and early

G. Gowda, et al.

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TABLE 2. Physico-chemical characteristics of Nethravathi estuary (Range and annual mean values) Parameters Stations 1 2 3 Temperature (0C)

24.25 - 32.1 (28.12)

25.4 - 31.6 (28.25)

24.05 - 31.8 (28.1)

Salinity (x10-3)

1.91 - 31.78 (19.59)

0.92 - 31.52 (16.8)

0.47 - 31.06 (15.15)

Nitrate - nitrogen (µg - at/l)

1.1 - 6.21 (2.37)

1.1 - 7.28 (2.74)

1.1 - 5.89 (2.55)

Phosphate - phosphorus (µg - at/l)

0.32 - 4.32 (1.170

0.27 - 1.08 (0.72)

0.1 - 3.76 (0.77)

values varied from 0.01 to 4.34. Predominance of phaeopigments to chlorophyll a was observed during Oct. - Nov, April and June with a range of 0.03 - 8.50 mg/m3. Phytoplankton Phytoplankton composed of diatoms, dinoflagellates, blue green algae, green algae and silicoflagellates with cell counts varing from 4.32 x 104 to 6.5 x 104 cells/ m3 (Fig. 2). Higher biomass was observed during April - May, June - July and Nov. - Dec. Green algae were most dominant during monsoon period, whereas, diatoms, dinoflagellates, blue green algae were observed during pre and postmonsoon. Estuaries along the west coast of India show higher production during pre and postmonsoon with the dominance of diatoms and dinoflagellates (Joseph and Pillay, 1975; Vijayalakshmi, 1986 and Patil, 1987). Temperature, salinity and nutrients Fig.3. Distribution of phytoplankton pigments (mg/m3) in the Nethravathi estuary, Mangalore.

postmonsoon period and values varied between 0.02 and 3.96. Chlorophyll b/c was high in May, July and Oct. - Nov. with a range of 0.02 - 5.17. The ratios of carotenoids to chlorophyll a was maximum during Nov. at all stations. The

Lower temperature was recorded during monsoon (24.25 - 26.05 0C), moderate during postmonsoon (25.45 - 27.90 0 C) and higher during premonsoon period (27.9 - 31.8 0C). During the corresponding periods salinity was 0.47 - 6.87 ppt, 3.04 - 28.98 ppt and 18.64 - 31.69 ppt respectively. Nitrate-nitrogen was high during monsoon and low during

Phytoplankton pigments in the Nethravathi estuary premonsoon. Phosphate was high during monsoon period and low during post and premonsoon period (Table 2). Nutrient enrichment was observed during the period of low temperature and salinity and vice-versa in Nethravati estuary.

Discussion Pigments are being used for systematic classification of phytoplankton (Riley and Wilson, 1965; Wright and Jeffery, 1987) and as biomarkers of particulate organic carbon (Mile et. al., 1993; Bianchi and Lambert, 1995). Chlorophyll a, b and c are the important pigments present in phytoplankton (Parsons et al., 1989), which showed trimodal distribution with higher production during April - May, June - July and Nov. - Dec. Peak periods of pigments coincided with higher production of phytoplankton. Similar observations were made in other estuaries of India (Joseph, 1982; Vijayalakshmi, 1986 and Nair, 1990). Diatoms were the chief components present during pre and postmonsoon season, whereas, green and blue green algae were more abundant during monsoon and postmonsoon period. Diatoms such as Ceretulina bergonii, Chaetoceros curvisetus, Coscinodiscus marginatus, Nitzschia seriata and dinoflagellate, Ceratium furca form bloom during April - May. Blue green algae like Oscillatoria sp., species of green algae like Cylindrocystis, Mougoetia, Spirogyra and diatoms such as Thallassionema nitzschiodes, Pluerosigma directum were common during June - July (monsoon) while species of Chaetoceros loranzianus, Ceratulina bergonii, Ceratium fucus, Ulothrix sp. were abundant during Nov. - Dec. (postmonsoon) period. Higher production of phytoplankton coincided the higher biomass of phytoplankton pigments in

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the other estuaries also. (Bhargava and Dwivedi, 1976; Ram et. al., 1984 and Desai et al., 1984). Species diversity was more during pre and postmonsoon period. During these periods salinity and temperature was high and condition of water was more stable which helped in high phytoplankton growth as temperature and salinity showed positive correlation with phytoplankton biomass (Qasim and Reddy, 1967; Thangaraj, 1984; Ram et al., 1984; Jagadeesan, 1986 and Gopinathan et al., 1994). Akpan and Offen (1993) opined that increased concentration of pigments are due to increased penetration of light, reduction of freshwater discharge, resuspension of microalgae and increased nutrient concentration. The lower temperature during monsoon due to cloudy sky, rainfall and high turbidity caused lower phytoplankton biomass (Qasim, 1980; Chandran, 1987 and Jagadeeshan, 1986). Adverse effect of salinity on the reproductive physiology was also reported (Qasim and Reddy, 1967). Chlorophyll c/a ratio indicates the physiological state of plankton and for a healthy plankton it should be less than one (Bhargava and Dwivedi, 1976). A low ratio of chlorophyll a to carotenoid would suggest a chlorite, unhealthy population (Ketchum et. al., 1958). Phytoplankton in the Nethravati estuary were healthy as the ratios were less than 1 excepting the bloom periods. Chlorophyll a showed positive relationship with phytoplankton (0.59); chlorophyll b with c (0.78), carotenoid (0.72), phaeopigment (0.90) and negative relation with salinity (-0.58). An inverse relationship was observed between chlorophyll a and salinity (Dehadrai, 1970), positive correlation with phytoplankton (Devassy and Goes, 1989) in Mandovi Zuari estuary.

G. Gowda, et al.

Acknowledgement The authors are grateful to the Director of Instruction, College of Fisheries for encouragement, technical advise and facilities provided.

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