Incorporating Non-Trophic Data into Food Web Models: An Alternative Perspective on the Ecological Impacts of Bivalve Aquaculture in Puget Sound, WA

Shellfish aquaculture has the potential to alter the structure and dynamics of marine food webs.  To better understand the ecosystem effects of increased shellfish aquaculture, we modified a marine food web model to include non-trophic interactions between farm structure and the surrounding community.  Specifically, we developed and applied habitat and behavioral mediation functions, where the abundance of one group (cultured bivalves and associated farm structure) influenced the interaction between two other groups in the food web.  The non-trophic effects associated with farm structure and harvesting activities were more influential on the surrounding community than the direct trophic impacts of increased cultured shellfish biomass.  Functional groups most sensitive to increased bivalve aquaculture included birds, flatfish, nearshore, demersal fish, and certain invertebrates (e.g., sea stars, predatory gastropods, and small crustaceans).  This study highlights the importance of understanding non-trophic relationships between bivalve aquaculture and the surrounding community. It also provides insight into the benefits and uncertainty of incorporating non-trophic data into a food web model.  Understanding these relationships will inform management decisions by clarifying tradeoffs in ecosystem functions and services in coastal estuaries and enable monitoring of direct and cumulative effects of bivalve aquaculture at a food web scale.