Freshwater mussels: species roles, ecosystem services and conservation

C.C. Vaughn, D.E. Spooner, H.S. Galbraith, K.L. Reagan, and D.M. Allen.Oklahoma Biological Survey and Department of Zoology, University of Oklahoma, Norman, OK, USA 73019

Freshwater mussels are a guild of long-lived, filter-feeders that link the water column with bottom sediments. We are using comparative field observations, field experiments, and laboratory experiments to ask: (1) What is the overall importance of the mussel guild to stream ecosystem function?; (2) Do species perform different ecological roles?; and (3) Do species roles vary with environmental context? Our results indicate that many ecosystem services performed by mussels (algal clearance, nutrient excretion, organic matter biodeposition) are linearly related to community biomass; thus, there is the potential for strong ecosystem effects when mussel biomass is high and hydrologic residence times are long. In comparative field studies and field experiments we have shown that living mussels provide biogenic structure and nutrients to other organisms; algal growth is higher on the shells of living mussels compared to shells alone, and macroinvertebrate richness and densities are higher on the shells of living mussels and in mussel patches than in other streambed areas. Field and laboratory experiments demonstrate strong effects of a potentially keystone species, Actinonaias ligamentina, on factors such as periphyton biomass, but comparatively weak diversity effects. In addition, species effects are context-dependent and regulated by abiotic factors such as temperature and flow.