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

Abstract

Estuaries are subject to diverse anthropogenic stressors, such as shellfish aquaculture, which involve extensive use of estuarine tidelands. Pacific oyster Crassostrea gigas aquaculture is a century-old practice in US West Coast estuaries that contributes significantly to the regional culture and economy. Native eelgrass Zostera marina also commonly occurs in intertidal areas where oyster aquaculture is practiced. Eelgrass is federally protected in the USA as ‘essential fish habitat’, restricting aquaculture activities within or near eelgrass. To contribute scientific information useful for management decisions, we sought to compare fish habitat use of oyster aquaculture and eelgrass, as well as the edges between these 2 habitats, in Willapa Bay, Washington, USA. Furthermore, given a recent shift towards off-bottom culture methods, in part to protect seagrasses, long-line and on-bottom oyster aquaculture habitats were compared. A combination of direct (underwater video, minnow traps) and indirect (predation tethering units, eelgrass surveys) methods were employed to characterize differences in fish habitat use. Eelgrass density declined within both aquaculture habitats but less so within long-line aquaculture. Most fish species in our study used long-line oyster aquaculture and eelgrass habitats similarly with minimal edge effects, and on-bottom aquaculture was used less than either of the other 2 habitat types. These results are consistent with previously observed positive relationships between fish abundance and vertical habitat structure, but also reveal species-specific behavior; larger mesopredators like Pacific staghorn sculpins were sighted more often in aquaculture than in interior eelgrass habitats.

De novo reefs: Fish habitat provision by oyster aquaculture varies with farming method

“…However, fish observations were higher for baskets than seagrass, perhaps reflecting the additional complex-ity that baskets add to the underlying habitat. Previous studies have likewise found similar invertebrate and fish communities between seagrasses and longline farms and between seagrasses and longlines with flipbag farms (Coe 2019, Muething et al 2020, Munsch et al 2021, although in some instances, long lines supported higher abundances but lower richness of fish than seagrass habitats (Dealteris et al 2004, Glenn 2016.…”

“…Mean (± SE) observations of bream as documented by 75 min remote underwater video deployments. Data are averaged across the 2 study years, as these did not significantly differ, with 4 cameras deployed on 3 replicate days of each season and year, to give n = 24. Letters above columns denote treatments that were significantly different (at α = 0.05) within each site and season by estimated marginal means structure can serve as important habitat to wild organisms, and there is growing evidence that off-bottom shellfish aquaculture can provide important fish habitat (Dealteris et al 2004, Mercaldo-Allen et al 2020, Muething et al 2020, Ferriss et al 2021) and trophic resources (Lefcheck et al 2019). Yet, uncertainty surrounding the impact of farm and infrastructure type on habitat provisioning functions remains a major knowledge gap which could inhibit the development of multifunctional shellfish aquaculture.…”

“…Previous studies that have found that shellfish farms can provide food and habitat to commercially important fish have come predominantly from Europe and the Americas (Dealteris et al 2004, Erbland & Ozbay 2008, Muething et al 2020, Ferriss et al 2021, Theuerkauf et al 2022). This study similarly documents that oyster farms provide important fish habitat in Australia.…”

“…The infrastructure provided by oyster farms can support communities of invertebrates and fishes with similar, or in some instances, greater biomass and abundance than adjacent habitats, including rocky reef, seagrass beds, mudflats and oyster reefs (Glenn 2016, Coe 2019, Mercaldo-Allen et al 2020, Muething et al 2020, Munsch et al 2021. However, how this service of oyster farms varies as a function of farming methodology is poorly understood (but see Theuerkauf et al 2022 for a metanalysis addressing this question).…”

Ecosystem Restoration: Enhancing Ecosystem Services with Floating Aquaculture

“…It is comprised of the biofouling community found in the top 30 cm growing on floating objects and a subset of natural reef community members that enter bags as propaguels or small swimming juveniles. In Beaufort NC and around the globe in temperate and tropical harbors about 95% of biofouling organisms are invasive species, many of which arrived with boats and trade before or with the first European settlers [51][52][53] . Though found in the immediate coastal ocean [24] biofouling communities are particularly adapted to live in polluted harbors [54] .…”