Reductions in distribution, photosynthesis, and productivity of eelgrass Zostera marina associated with oyster Crassostrea virginica aquaculture

Abstract

This study provides the first quantitative description of the influence of suspended bag oyster aquaculture (SBOA) of Crassostrea virginica on the distribution, morphology, physiology, and productivity of eelgrass Zostera marina. We explored possible mechanisms related to decreased light availability, nutrient stress, organic loading, and physical damage from bags or boats. Surveys at multiple spatial scales across a 125 km range of Atlantic Canadian bays and estuaries demonstrated consistent declines in eelgrass biomass by as much as 79% at commercial culture leases versus reference areas. Reductions in biomass were negatively related to both oyster stocking density and the age of culture leases. We further observed reductions in the capacity of eelgrass photochemistry at culture sites, accompanied by primary production declines of 37.9%. Our data suggest that these reductions in Z. marina distribution, productivity, and photosynthetic rates are primarily occurring as a result of light limitation caused by shading from aquaculture equipment. © Fisheries and Oceans Canada 2013.