Studies on the Periphytic Algae in pokkali and prawn fields of N Paravoor and Vypeen Island

Abstract

The backwaters of Kerala support as much biological productivity and diversity as tropical rain forest. They are also responsible for the rich fisheries potential of the state. The pokkali and prawn fields are highly productive ecosystems. Pokkali and prawn fields of N. Paravoor and Vypeen Island are located eastern and western side of Vembanad kayal and Cochin estuarial system. Pokkali is unique paddy cultivation practiced mainly in three districts of Kerala. Ernakulam district in which both N. Paravoor and Vypeen Island include has more pokkali field than other districts. The farming systems followed in the pokkali land is internationally acclaimed as a sustainable system. The integration of paddy and prawn rotationally with the change in the field water salinity tunes well with the rhythm of nature. Prawn fields are permanent fishing ponds. Enhancement of fish production though periphyton growth is well documented. Ten sites both pokkali and prawn fields were selected from the area to assess the temporal and spatial variation of periphytic flora, physicochemical parameters, primary production and water quality. Qualitative and quantitative analysis of periphytic flora were carried out. The physico-chemical parameters such as temperature, dissolved oxygen, pH, salinity, phosphate, silicate, nitrite and nitrate, photosynthetic pigments, autotrophic index, assimilation number and primary productivity were estimated. During the present investigation a total 245 periphytic algae were recorded. Out of the 245 organisms 185 were of Bacillariophyceae, 34 Myxophyceae, 24 Chlorophyceae and 2 from Euglenineae. The monthly average periphyton cell number in the study area varied from 4.4x103 to 6.4x104 cells cm-2. The highest cell numbers in the study area recorded was 3x105 cells cm-2.The annual mean concentration of Chl. a recorded was 18.794 ± newline12.129 mg m-2. The annual mean periphytic primary production estimated was 66.401 ± 40.308 mg C m-2 h-1. The monsoon season recorded the highest production.