Body size affects lethal and sublethal responses to organic enrichment: evidence of associational susceptibility for an infaunal bivalve

Eutrophication is an increasing problem worldwide and can disrupt ecosystem processes in which macrobenthic bioturbators play an essential role. This study explores how intraspecific variation in body size affects the survival, mobility and impact on sediment organic matter breakdown in enriched sediments of an infaunal bivalve. A mesocosm experiment was conducted in which monocultures and all size combinations of three body sizes (small, medium and large) of the Sydney cockle, Anadara trapezia, were exposed to natural or organically enriched sediments. Results demonstrate that larger body sizes have higher tolerance to enriched conditions and can reduce survival of smaller cockles when grown together. Also, large A. trapezia influenced sediment organic matter breakdown although a direct link to bioturbation activity was not clear. Overall, this study found that intraspecific variation in body size influences survival and performance of bioturbators in eutrophic scenarios.