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Title: On the edge: assessing fish habitat use across the boundary between Pacific oyster aquaculture and eelgrass in Willapa Bay, WA

Author
item MUETHING, KELLY - Oregon State University
item TOMAS, FIONA - Oregon State University
item WALDBUSSER, GEORGE - Oregon State University
item Dumbauld, Brett

Submitted to: Aquaculture Environment Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2020
Publication Date: 12/3/2020
Citation: Muething, K.A., Tomas, F., Waldbusser, G., Dumbauld, B.R. 2020. On the edge: assessing fish habitat use across the boundary between Pacific oyster aquaculture and eelgrass in Willapa Bay, WA. Aquaculture Environment Interactions. 12:541-557. https://doi.org/10.3354/aei00381.
DOI: https://doi.org/10.3354/aei00381

Interpretive Summary: Estuaries serve as ecological links between terrestrial, freshwater, and marine systems, but are subject to diverse stresses from humans. Along the US West Coast, shellfish aquaculture is one potential stress agent because it involves extensive use of estuarine tidelands. Pacific oyster (Crassostrea gigas) aquaculture is a century-old practice that significantly contributes to the regional culture and economy, but overlaps the distribution of the native seagrass (eelgrass, Zostera marina). Seagrasses are recognized to provide nursery habitat for many commercially harvested species of fish and invertebrates. Eelgrass is federally protected as “essential fish habitat” and aquaculture activities within or near eelgrass are restricted. We characterized use of both aquaculture and eelgrass habitat by fish in order to better inform such management guidelines and focused on two questions: 1) what is the role of habitat edges or boundaries between these two habitats in the larger seascape, and 2) does aquaculture method affect this response. Direct (underwater video) and indirect ( predation tethering units) methods were used to quantify fish distribution and behavior along a gradient between aquaculture and eelgrass in each type of aquaculture. Results suggest that most fish species use long-line oyster aquaculture and eelgrass habitats similarly with minimal edge effects, but on-bottom oyster aquaculture was less used than the other two habitat types. Though results differed by species, they are consistent with previously observed positive relationships between fish abundance and vertical habitat structure.

Technical Abstract: Estuaries serve as ecological links between terrestrial, freshwater, and marine systems, but are subject to diverse anthropogenic stressors. Along the US West Coast, shellfish aquaculture is one potential stressor as it involves extensive use of estuarine tidelands. Pacific oyster (Crassostrea gigas) aquaculture is a century-old practice that significantly contributes to the regional culture and economy. Native eelgrass (Zostera marina) also commonly occurs in intertidal areas where oyster aquaculture is practiced. Seagrasses provide nursery habitat for many commercially harvested species and have recently garnered more conservation interest because of widespread decline. Eelgrass is federally protected as “essential fish habitat”, restricting aquaculture activities within or near eelgrass. To inform associated management decisions, we sought to characterize habitat use of aquaculture and eelgrass by fish. Two perspectives shaped the investigation: 1) seascape ecology, highlighting the role of edge effects, and 2) aquaculture method where. Aa recent shift towards off-bottom culture methods, in part to protect seagrasses, precipitated a comparison between long-line and on-bottom aquaculture. Direct (underwater video) and indirect (e.g. predation tethering units) measures of fish distribution and behavior were used to quantify differences along a transect between aquaculture and eelgrass in each type of aquaculture. Results suggest that most fish species use long-line oyster aquaculture and eelgrass habitats similarly with minimal edge effects, but on-bottom aquaculture was used less than the other two habitat types. These results are consistent with previously observed positive relationships between fish abundance and vertical habitat structure but appear to reflect individual species behavior and use of these intertidal habitats.