Intertidal community structure differs significantly between substrates dominated by native eelgrass (Zostera marina L.) and adjacent to the introduced oyster Crassostrea gigas (Thunberg) in British Columbia, Canada
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Eelgrass beds represent important habitats for marine organisms, but are in decline in many coastal areas around the world. On Cortes Island, British Columbia, Canada, oysters coexist regionally with native eelgrass (Zostera marina L.), but eelgrass is typically absent directly seaward of oyster beds (the “below-oyster cobble zone”). We compared assemblage structure of nekton (fish and swimming macroinvertebrates) and epibenthos (macroinvertebrates and macroalgae) between eelgrass bed and below-oyster habitats. We sampled the intertidal zone on Cortes Island at low tide using two methods: quadrats to enumerate epibenthic macroinvertebrates and macroalgae, and beach seines to enumerate fish and swimming macroinvertebrates. Using multivariate analysis of similarity (ANOSIM), we found that the structure of nektonic and epibenthic assemblages associated with below-oyster cobble zones were significantly different from those in eelgrass-beds. Univariate measures showed that nektonic species richness and abundance were significantly higher in eelgrass beds than in below-oyster cobble habitat, whereas epibenthic species richness and abundance were significantly higher in below-oyster habitat.
KeywordsSeagrass British Columbia Epibenthic invertebrates Fish Macroalgae
We wish to acknowledge logistical and field support of Mathew Brechtel, Michael, Sierra, Marg and Sully Sullivan, Heidi, Ruth and Fred Zwickel, and Chris Williamson. Research was supported by an NSERC Post Graduate Scholarship to JRK and an NSERC Discovery Grant and NSERC/SSHRC MCRI to JPV. We also thank two anonymous reviewers for their comments.
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