Graduate Thesis Or Dissertation

Utilization of the Non-Native Seagrass, Zostera japonica, by Crab and Fish in Pacific Northwest Estuaries

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  • The introduction of non-native species often results in fundamental changes in the structure and function of disturbed environments. In the Pacific Northwest (PNW), the introduced seagrass Zostera japonica is rapidly expanding in distribution, impacting stakeholders and public use of the intertidal. Z. japonica’s expansion has prompted a number of different management strategies and many research studies that examine its ecology in the PNW. A number of studies have compared the benthic and epifaunal communities in Z. japonica to those of the native Z. marina, but to date, none have contrasted the nekton communities using the two seagrasses. The goals of this project were to 1) examine the community composition of a variety of available estuarine habitats in Willapa Bay, Washington, and Yaquina Bay, Oregon, via paired deployment of cameras and small fish traps; and 2) to explore the different management strategies used in the PNW and identify strengths and weaknesses associated with invasive species management, as indicated by short interviews with professionals working on Z. japonica. In Willapa Bay, Z. japonica, Z. marina, clam aquaculture, and on-ground oyster aquaculture were examined. In Yaquina Bay, Z. japonica, Z. marina, and bare substrate were examined. A total of 11 species, with 10 occurring in Willapa Bay and 9 in Yaquina Bay, were observed in video footage. Habitat was a significant predictor of catch per unit effort (CPUE) for the most abundant species in Yaquina Bay but not those in Willapa Bay. Community composition was significantly different between habitats in each bay but not between the bays. Explicit comparisons of seagrass habitat in each bay indicate some evidence that community composition of the two seagrasses differs in Yaquina Bay, but not in Willapa Bay. We conclude that community composition varies little between seagrass structure in Yaquina Bay and Willapa Bay and that local variation is highly dependent on the availability of structured habitats. Additionally, the distribution of Z. japonica relative to Z. marina may drive these differences in community composition between seagrass habitats in these estuaries. In short, unstructured interviews with professionals working on Z. japonica in the PNW, ecological characteristics that prompted management consideration; historical and potential management approaches; and suggestions to improve invasive species management at the local, regional, and national levels were discussed. Interview participants highlighted Z. japonica's expansion into historically unstructured regions of the intertidal, its role as an ecosystem engineer, and the intrinsic value of the local, native ecology as reasons for management. The need for collaboration across all levels (local, state, regional, and federal) of invasive species management, public outreach and education, professional development, and explicit statement of management position were all stressed as potential improvements to invasive species management.
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