Influence of intertidal Manila clam Venerupis philippinarum aquaculture on biogeochemical fluxes

Bivalve aquaculture introduces high densities of farmed organisms to the natural environment with potential consequences on a number of ecosystem processes, including modification of nutrient fluxes (e.g. NH4, NOX, PO4, and Si(OH)4) and benthic respiration, and may impact benthic communities. Infaunal clam culture may influence the environment due to the clams themselves [their metabolic processes (e.g. feeding, respiration), production of faeces/ pseudo faeces, and/or trapping of organic matter], the farm structures, or the fouling on these structures. This study examined how farmed Manila clams Venerupis philippinarum, the nets placed on beaches to protect them from predators, and the fouling organisms growing on these nets modify nutrient fluxes, benthic respiration, and benthic community structure in coastal British Columbia, Canada. In 2012, a manipulative experiment involving sixty 2.25 m2 plots and 6 treatments was conducted on an intertidal farmed beach to evaluate the effect of clams (presence/ absence) and net status (fouled, cleaned, and absent). Percentage organic matter in the first centimetre of sediment was significantly greater with the presence of clams than without. The abundance and taxonomic richness of organisms in sediments were significantly affected by net status. Nutrient fluxes and oxygen consumption increased significantly with the presence of clams, the latter also increasing with the presence of nets and fouling on nets (incubated under dark conditions). These results show that farmed clams and the structures used to culture them influence several environmental parameters, and provide a better understanding of the role of these factors in modulating the benthic environment.