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Marine Ecology Progress Series

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MEPS 424:87-95 (2011)  -  DOI:

Native clams facilitate invasive species in an eelgrass bed

Laura F. White1,2,*, Lindsay C. Orr2,3

1Department of Zoology, University of British Columbia, 6270 University Blvd., Vancouver, British Columbia V6T 1Z4, Canada
2Bamfield Marine Sciences Centre, 100 Pachena Road, Bamfield, British Columbia V0R 1B0, Canada
3Department of Biology, University of Victoria, Victoria, British Columbia V8W 2Y2, Canada

ABSTRACT: Whether the non-native seaweed Sargassum muticum can displace or impact native eelgrass Zostera marina has been debated in the literature, based on differing substrate requirements of the 2 species. Field observations in Bamfield, British Columbia, Canada, revealed that the non-native S. muticum successfully inhabits an eelgrass bed through colonizing siphons of the native clam Tresus capax. Numerical or physical facilitation of S. muticum into the eelgrass bed by T. capax may be tempered by seaweed quality or condition. We used field sampling to investigate whether seaweed condition differs between 2 attachment substrates (clam siphon and rock) as a proxy for habitat quality. Attachment substrate promoted different morphologies of S. muticum; individuals attached to clam siphons expressed morphologies consistent with sheltered areas compared to individuals attached to rock, which expressed wave-exposed morphologies. Habitat association with the different morphologies supported differences in the epibiont communities colonizing S. muticum. Further, S. muticum subsequently facilitated incursion of the non-native tunicates Styela clava and Botrylloides violaceous into the eelgrass bed through habitat provisioning. By facilitating 2 additional invaders, S. muticum enhances the level of invasion in the eelgrass bed. This non-native seaweed has the potential to disrupt the persistence of eelgrass in this system.

KEY WORDS: Sargassum muticum · Zostera marina · Non-native species · Facilitation · Tresus capax

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Cite this article as: White LF, Orr LC (2011) Native clams facilitate invasive species in an eelgrass bed. Mar Ecol Prog Ser 424:87-95.

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