The role of infaunal functional and species diversity in short-term response of contrasting benthic communities to an experimental food pulse

Abstract

Benthic communities play a major role in organic matter remineralization but the role played by macrofauna functional and taxonomic diversity remains elusive. To investigate this topic, we collected sediment cores from two different continental shelf locations near British Columbia, Canada, that differed in diversity to determine how the communities would respond to organic enrichment in the short term (~24h). We added phytodetritus to half of the cores, measured benthic oxygen and nutrient fluxes in natural and enriched incubations, identified macrofauna, and calculated a suite of functional and taxonomic diversity indices. We found that benthic communities in Saanich Inlet (SI) and the Strait of Georgia East (SoGE) differed significantly in composition and that this difference corresponded to significant differences in benthic flux rates between sites. Multivariate analyses showed that the higher taxonomic (Simpson's diversity) and functional richness (FRic) observed in SoGE explained generally higher benthic flux rates at SoGE compared to SI. In enriched incubations, the higher species richness observed at SoGE explained most of the enhanced benthic flux rates measured in SoGE compared to SI. Our study also identified mean densities of detritivores and omnivores as primary predictors of the higher benthic flux rates measured in enriched incubations in SoGE compared to SI. These results suggest that detritivores and omnivores are the first functional groups of macrofaunal organisms to ingest fresh phytodetritus on the seafloor, and point to their primary importance in short-term remineralization of organic matter following phytoplankton bloom deposition on the seafloor. Our results further indicate that sediments with higher functional diversity may process organic matter and regenerate nutrients more quickly than lower diversity sediments, and that diversity loss may have negative consequences for ecosystem functioning of continental shelf sediments.