The Effect of Manila Clam Aquaculture on Invertebrate Diversity

Abstract

The success of commercial shellfish aquaculture is rooted in a healthy and productive nearshore marine ecosystem, making it essential to strike a balance between ecological and economic interests for farmers and regulators alike. Consequently, the removal of marcoalgae from anti-predator nets and the development of new harvest techniques used in Manila clam (Venerupis philippinarum) aquaculture have raised important questions regarding their ecological impacts. In this study, I examine these impacts on the infaunal invertebrate communities of a Manila clam farm in Samish Bay, Washington. Using species data gathered from benthic and epibenthic sampling, I found that farmed sites support different invertebrate communities compared to reference sites, regardless of whether or not macroalgae is removed from anti-predator nets. Similarly, farmed sites support different invertebrate communities and lower taxon densities and richness values when compared to eelgrass habitats, regardless of whether or not sites are harvested by hand or by machine. Within farmed sites, however, a significant decline in both density and richness was observed after hand harvesting events, but not after mechanical harvests. These results provide ecological evidence that supports the removal of macroalgae from anti-predator nets, and the continued use and development of mechanical forms of Manila clam harvest. Both technologies are responsible for increases in the economic returns from shellfish operations, but until now, their ecological effects have been less clear.