A comparison of epifaunal invertebrate communities in native eelgrass Zostera marina and non-native Zostera japonica at Tsawwassen, BC

Abstract

The introduction of non-native species can alter the structure of local communities and ecosystems. Although there is concern over the negative effects imposed by introduced species, positive effects are also possible. Introduced species may facilitate local resident species by providing or modifying habitat; these positive effects are sometimes overlooked, but are important for decisions about the local management of non-native species. The introduction of Zostera japonica to the Northeast Pacific coast is a case of a non-native foundation species that appears to expand total eelgrass habitat area, potentially facilitating local eelgrass-inhabiting species. In this study, we asked whether the non-native Z. japonica provides habitat for eelgrass-dwelling invertebrates that is similar to its native congener, Z. marina. We systematically quantified invertebrate assemblages in the two eelgrass species and quantified eelgrass characteristics that are relevant to epifaunal habitat quality (e.g. shoot density and surface area). We found that Z. japonica supports a greater total abundance of the same invertebrate species found in Z. marina meadows; however, the relative abundance of invertebrate species differed between Z. japonica and Z. marina. This result is consistent with differences in the two congeners’ morphological characteristics, density of vegetative and reproductive shoots, and total blade surface area per square metre. We conclude that the expansion of total eelgrass habitat due to the introduction of Z. japonica appears to increase the available habitat for local epifaunal invertebrate communities.

Key words:

• Facilitation
• foundation species
• invertebrates
• non-native species
• Northeast Pacific
• Zostera

Acknowledgements

We are grateful to Sarah Amundrud, Boaz Hung, Andrew Primavera, Patricia Sun and Nick Uthaikhaifar for their assistance with data collection and for their feedback. We would like to thank Alan Lewis for providing information on local copepod species. We also thank Natalie Caulk, Andrew Huang, Ross Whippo, Sally Hacker, Franz Uiblein and two anonymous reviewers for providing helpful comments on the manuscript.

Editorial responsibility: Sally Hacker

Additional information

Funding

This study was funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) discovery grant to M.I.O.