Biological Studies on some Bivalves

The biomass of the molluscs is very important to ecosystems. In marine environments, molluscs may form the dominant group, especially in their larval stage, but also on soft substrates (bivalves), and on hard substrates, where some molluscs such as Pearl oysters (Pinctada) and mussels may be more important in terms of their biomass than corals (Van Bruggen, 1995). In freshwater environments biomass of molluscs is significant in some environments: for example in temperate countries lake bottoms may be covered with the small bivalves from families Sphaeriidae and Pisidiidae. In tropical areas, the same can be true. Brown (1994) summarises much of the data available on contribution of molluscs to the biomass of freshwater systems in Africa, and shows that prosobranchs contribute the major part in Lakes, such as Chad, Malawi, Tanganyika and Victoria. Molluscs in the man-made Lake Kariba made up nearly the entire biomass of the benthic animals (Prosobranchs 4.1 % and Bivalves 95.8%) (Machena and Kautsky, 1988).