MICRODISTRIBUTION AND ABUNDANCE OF FRESH-WATER MUSSELS (MOLLUSCA, UNIONACEA AND CORBICULACEA) IN SUZANA LAKE, SOUTHERN BRAZIL

Freshwater mussels from a small lake in southern (subtropical) Brazil are analized in their distribution and abundance. The mussels were sampled through transects using quadrats of 1 m-2. The individuals were manually collected with SCUBA and free diving. Data on substrate type, percentual of plant cover and depth were also recorded. A total of 443 m-2 were sampled in the lake. Four species of Unionacea (Diplodon charruanus, Anodontites trapesialis, Anodontites (cf.) patagonicus, Monocondylaea minuana) and two of Corbiculacea (Neocorbicula limosa and Corbicula fluminea) are registered. D. charruanus was the most abundant species, occurring in the over-all substrates with the greatest mean density (ind. m-2) in the muddy sand subset of the lake. The lowest mean density of this species is on the pure mud subset. M. minuana was restricted to a band of 1.0 - 1.5 m of depth, sandy substrate. There are indicatives of a crash in the population of A. trapesialis. Only five individuals of A. (cf.) patagonicus were registered. N. limosa and C. fluminea apparently are restricted to a sand shore near and into the outlet channel, though the population of the exotic C. fluminea seem is on the rise.