Diversity and species composition of phytoplankton from the Mandaitivu Coast, Sri Lanka, and the water quality parameters influencing them.

C.N.S.Wijesundara^*, K. Sivashanthini

Department of Fisheries, Faculty of Science, University of Jaffna, Jaffna, Sri Lanka

^*cnethmalie@gmail.com

Abstract

Mandaitivu coast is located in the Jaffna District, Northern Province, Sri Lanka possess high productivity indicated by the high diversity of phytoplankton. The research aimed to identify the diversity of phytoplankton in the study area and to find out the influence of water quality parameters on phytoplankton diversity. Plankton and surface water samples were collected monthly from the study site for analysis of phytoplankton diversity and water quality parameters respectively. The result revealed that the minimum and maximum values for pH, water temperature, air temperature, dissolved oxygen (DO), phosphate, nitrate, and total dissolved solid were 7.97-8.41, 28–31 °C, 32–37 °C, 5.04– 7.05 mg l^-1, 0.13-0.19 mg l^-1, 0-5.6 mg l^-1, and 25-32 mg l^-1respectively. A total of 40 species of phytoplankton belonging to 21 families were identified in the study. The high density of phytoplankton (10000 cellsL^-1) was recorded in the month of January while the chlorophyll- content was 3.7784 µgL^-1 which reveals the high productivity of the ocean. High population density and species diversity during January and February might be due to the influence of water quality parameters and the predominance of diatoms such as Thalassiothrix frauenfeldii, Cylindrotheca Closterium, Coscinodiscus radiatus, Licmophora sp., Climacosphenia elongate, Pleurosigma normanii and Nitzchia spp. The descending order of percentage contribution of each group of phytoplankton was Diatoms>Cyanobacteria>Blue greens>Dinoflagellate. Canonical correspondence analysis (CCA) expressed that the water quality parameters significantly influence the distribution of the phytoplankton in Mandaitivu coast. The abundance of family Coscinodiscacea showed a significant (P<0.05) positive correlation with the TDS, actual conductivity, and salinity. It also reveals that nutrient content (Nitrate and Phosphate) had a significant (P<0.05) association with most phytoplankton families.

 Keywords- Plankton, Phytoplankton, water quality

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