Distribution and Diversity of Economically Important Bivalves and Shrimps in Rekawa Lagoon in Sri Lanka

Abstract

The present study was undertaken to study distribution, diversity and correlation of bivalves and shrimps community in relation to environmental factors in Rekawa lagoon. Samples were randomly obtained from 19 selected sites in Rekawa lagoon and were separated by wet sieving method and identified up to family and genus level. In addition to that available mangrove species, sea grasses, soil texture, plankton diversity were recorded to investigate their correlation with bivalves and shrimp. Two types of benthic bivalves belonging to family Corbiculidae were identified up to the family level and they were most abundant in Parappuwa. Macrobrachium sp, and Atya sp. were recorded as shrimp species in the lagoon. In addition to that Pseudocalanus elongates, Calanus sp. and Naviculasp., were identified as planktons. Mean pH, ambient temperature, salinity, dissolved oxygen, water temperature and depth values of the lagoon were respectively 7.5, 36.3 C0, 21ppt, 11.2mg/L, 31.6 C0, and 70.3cm. Sand, clay and muddy soil textures were identified. Sea grasses Halophilaovalis, Hallophila, H. minor and Ruppia maritime and mangroves such as Aegicera scorniculatum, Avicennia marina, Avicennia officinalis, Bruguiera sexangula, Ceriopstagal, Excoecaria agallocha, Heritiera littoralis, Lumnitzera racemosa, Nypa fruticans, Rhizophora mucronata and Sonneratia caseolaris were among the identified species. In this study a significant correlation (p<0.05) between sea grass Halophila, H.ovalisand both Macrobrachium Sp. and Atya Sp.,water temperature and distribution pattern of Atya species, salinity level and Macrobrachium Sp., Dissolved Oxygen and Macrobrachium Sp., and water depth and Atya Sp. were observed. Shrimp fishery was observed as the main economic activity while Penaeus indicus, Penaeus monodon, Penaeus semisalcatus, Macrobrachium rosenbergii were recorded in the lagoon and off shore catch. Though diversity of bivalves is very low in Rekawa lagoon, diversity and availability of shrimp is very high due to government shrimp stocking programs and favorable water quality parameters.