The dynamics of habitat-forming species can reverberate throughout an ecosystem, and the disturbance of these species may therefore have wide-ranging effects. Eelgrass (Zostera marina) forms marine meadow habitats that host epi- and infaunal invertebrates as well as fish of commercial interest. The geoduck clam (Panopea abrupta) is one infaunal bivalve that can be found in natural association with eelgrass, but here we explore a recent, and artificial, association of the two species that results in the disturbance of eelgrass. Intertidal farming of the geoduck is a new and lucrative industry in the Pacific Northwest, and the ecological impacts of this practice are unknown. In cooperation with shellfish farmers, we documented the effects of geoduck harvest in a farm where eelgrass and aquaculture overlap, in Samish Bay, Washington. Before and after harvest, we assessed eelgrass demography and morphology, sediment texture and organic content, and infaunal richness and abundance. We hoped to trace the contemporaneous, and possibly causal, changes in the habitat-forming eelgrass alongside changes in abiotic and biotic characteristics of the eelgrass meadow.
Results/Conclusions
After harvest, within the farmed zone, we found significant decreases in eelgrass density, shoot size, and rates of flowering, and significant decreases in sediment organic content and elevation. We found no significant change in the patchiness of eelgrass or in the texture of sediment, and no evidence of spillover effects across the farm boundary. Our results suggest that geoduck harvest has detectable effects on the habitat-forming eelgrass, and that these effects are confined to the zone of aquaculture activity. As this project continues, our data will inform regulatory practices that seek to balance a sustainable aquaculture industry with ecosystem function.
