The functional diversity of marine communities is thought to influence community processes; thus the loss of taxa alters community function. Florida Bay was once populated by a diverse community of sponges before perturbations critically reduced their density and diversity. Given the impressive filtration rates of sponges and their role in nitrogen cycling among other ecological processes, the effects of sponge losses on community function are potentially great. To date, most studies of the effects of sponges on water column constituents have focused on measurements of individual species. However, sponges do not occur naturally in monoculture and no study has tested how changes in sponge communities affect planktonic communities and the biogeochemistry of the water column. We manipulated sponge biomass and diversity in outdoor flume-like mesocosms to determine the effect of functional diversity and water velocity on sponge filtration and nutrient conversion, measured as concentrations of nutrients, chlA, bacteria, and viruses.
Results/Conclusions
Generally, species-rich sponge assemblages functioned at a higher level (e.g., greater bacterial removal) than the equivalent biomass of species in monoculture. However, evidence of transgressive over-yielding (i.e., when species-rich replicates outperform monocultures) varied among species, the filtration effects of some being greater in monoculture than in high diversity combinations.