ANTHROPOGENIC IMPACTS OF NEAR-SHORE ACTIVITY ON THE MOLLUSCAN COMMUNITIES IN LAKE TANGANYIKA, AFRICA

Abstract

In recent decades, increased near-shore agriculture and urbanization surrounding the large lake basins of the African Rift Valley have led to increasing rates of sedimentation and nutrient loading. These environmental changes can impact benthic habitats through altering substrates, suffocating feeding appendages, and accumulating organic matter on the lake floor. Whereas the response of marine benthos to similar anthropogenic effects is increasingly documented, freshwater environments have been historically understudied. Consequently, our understanding of freshwater benthic response in areas at-risk of sedimentation is limited. Using extensive shell beds of mollusks collected from 9 to 20m along three coastlines of Lake Tanganyika, I reconstructed the taxonomic, functional feeding, and taphonomic composition of benthic communities. Results indicate an inverse taxonomic and functional community composition across sites, driven by substrate type and organic matter concentrations. N. tanganyicense, a gastropod with mixed detritivore/suspension-feeding habits, along with numerous algivore/grazing gastropods, were abundant in muddy, organic-rich areas, whereas a suspension-feeding unionid bivalve, G. burtoni, thrived in sandy, organic-limited substrates. After performing taxonomic rank-order and similarity metrics on each site, results indicate a taxonomic discordance trend in organic-rich substrates similar to that found in areas experiencing anthropogenic eutrophication. The findings also suggest broader relevance for understanding taxonomic and functional tolerances, indicating that relationships among molluscan functional feeding groups could serve as biological indicators of organic-rich substrates.