Graduate Thesis Or Dissertation
 

Functional Comparison of Longline Oyster Aquaculture and Eelgrass (Zostera marina L.) Habitats Among Pacific Northwest Estuaries, USA

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/44558k18z

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  • Understanding the ecological role of Pacific oyster aquaculture (Crassostrea gigas) and eelgrass (Zostera marina L.) as important habitats in US Pacific Northwest estuaries is critical for management and regulatory decisions. The oyster aquaculture industry is currently restricted by regulations concerning impacts of their activities on Z. marina. This seagrass is protected under several legislative designations including Essential Fish Habitat (EFH) for federally managed fish species under the Magnuson Stevens Act. To date, federal and state regulations do not consider aquaculture as functional ecological habitat. While estuarine habitats serve multiple functions, the focus of our study was to evaluate fish and crab use. Underwater digital video surveys and minnow traps were used to quantify fish and crab abundance and behavior in longline oyster aquaculture, eelgrass beds, and the edge between these two habitats. Standardized predation tethering units (PTUs) were also deployed in each of these habitats to examine predation risk and refuge value. Our objective was not only to determine what fish and crab species were present, but also to determine whether their behavior could be used to clarify the functional role of these habitats and compare results among estuaries. Although there were no differences among habitat types in minnow trap catch, shiner perch (Cymatogaster aggregata) and Pacific staghorn sculpin (Leptocottus armatus) were the most common fish taken in all three estuaries. Shiner perch were sighted in Samish Bay video more frequently in longline aquaculture than in eelgrass while Pacific staghorn sculpin were more frequently sighted on the edge than in either oyster aquaculture or eelgrass. Additionally, behavior of fish and crab did not differ among habitat types in Samish Bay. Results of predation assays suggested that predation pressure was highest in Tillamook Bay and lowest in Samish Bay where an apparent edge effect is consistent with higher abundance of Pacific staghorn sculpins. While benthic structure provided by both eelgrass and oysters has previously been shown to be important, our results suggest that the form of the benthic structure (e.g. off-bottom versus on-bottom) and features such as edge habitats may also play an important role in PNW estuaries.
  • Keywords: Humboldt Bay, Tillamook Bay, Samish Bay, relative predation intensity, eelgrass, video camera surveys, fish and crab assemblage, longline oyster aquaculture, ecosystem based management
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