The Role of Eelgrass in Marine Community Interactions and Ecosystem Services: Results from Ecosystem-Scale Food Web Models

Eelgrass beds provide valuable refuge, foraging and spawning habitat for many marine species, including commercially valuable species such as Pacific salmon (Oncorhynchus spp.), Pacific herring (Clupea pallasii), and Dungeness crab (Metacarcinus magister).  We used a food web model of central Puget Sound to examine how the marine community responds to changes in coverage of native eelgrass (Zostera marina), spanning 0% to 200% of current coverage.  Seventeen of the model’s 62 functional groups responded strongly (|slope| >10%) to varying eelgrass coverage, primarily due to food web effects mediated through groups that use eelgrass as habitat; 14 of those 17 groups responded positively to increased eelgrass coverage, including wild salmon groups, juvenile Pacific herring, Dungeness crab, and rockfish (Sebastes spp.).  We then associated various groups with several consumptive and non-consumptive ecosystem services.  Increased eelgrass coverage was most associated with increases in consumptive services (e.g., recreational harvest and total value of commercial fisheries), while decreased eelgrass coverage resulted in sharp declines in consumptive services as well as some non-consumptive services (e.g., beach combing, bird watching).  We saw little evidence of tradeoffs among marine resources; that is, increasing eelgrass coverage was essentially either positive or neutral for all services we examined, although we did not examine terrestrial activities (e.g., land use) that affect eelgrass coverage.  Ongoing improvements in ecosystem model performance and in how ecosystem services are defined and measured are essential in order for these methods to properly inform management decision-making.