Spatial distribution of live and dead bivalves in saltwater lake Malo jezero (Mljet National park)

There is a lack of knowledge on bivalve species in the lake Malo jezero. This paper deals with spatial distribution of bivalves with the aim of getting better understanding of ecological conditions in this protected area. A study of bivalves was conducted at 25 stations in saltwater lake Malo jezero in 1998. Bivalve samples were collected with the SCUBA using a specially designed hand-dredge. Sediment samples were collected by dragging a small plastic container along adjacent sediment surface. A total of 31 bivalve species were identified, of which all but five could be identified to the species level. Live individualswere found four fourteen of these species. Gastrana fragilis, Psammobia fervensis, Tapes decussatus and Mysia undata were found for the first time in Malo jezero. Statistical analyses of samples established the difference in spatial distriibution of bivalves with respest to depth: both the number of bivalve species and the number of specimens decreases with increasing depth. Stations of the same or similar depths, located in different parts of the lake, had a high index of faunistic similarity. Sediment type was correlated with the changes in depth: the proportion of sand decreases and the proportion of mud increases with increasing depth. The results of this study indicate that sediment is one of important abiotic factors that restrict the spatial distribution of bivalves to shallow parts of lake Malo jezero, and that living bivalves are all represented in locally accumulating death assemblage.