First Advisor

Catherine de Rivera

Term of Graduation

Fall 2021

Date of Publication


Document Type


Degree Name

Master of Science (M.S.) in Environmental Science and Management


Environmental Science and Management




Carcinus maenas, Zostera marina, Introduced organisms, Estuarine ecology



Physical Description

1 online resource (v, 60 pages)


Eelgrass (Zostera marina) plays a critical role in estuarine ecosystem function by sustaining a variety of marine and freshwater species, but it's increasingly threatened by the aggressive non-native green crab (Carcinus maenas). The abundance of C. maenas is on the rise within the coastal environment of Oregon and it is imperative to know how these populations will affect the long-term health of Z. marina. C. maenas have been linked to declines in Z. marina coverage and shellfish abundance, but there has been no research on to what extent the density of Z. marina affects its capability to survive despite C. maenas activity. Z. marina density is decreasing globally, leaving beds more vulnerable to disturbance and reducing options for recovery after disturbance. We tested the hypothesis that greater loss in Z. marina coverage would occur at low densities because the sparse rhizome mat could be easily uprooted by C. maenas. We conducted an enclosure experiment in Netarts Bay, OR to analyze change in Z. marina coverage and health over the span of two weeks with or without C. maenas. Low density Z. marina experienced a greater decrease in coverage regardless of C. maenas presence. We also observed greater loss in Z. marina coverage in plots with C. maenas. However, the interaction between Z. marina density and C. maenas activity on overall Z. marina survival and health was not statistically significant. Given that C. maenas contributed to the loss in Z. marina coverage and low density Z. marina was vulnerable to any type of disturbance removal of C. maenas would be beneficial across Z. marina densities. These observations suggest that efforts to restore Z. marina should include replanting at high densities to create more resilient beds.


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