Native clams facilitate invasive species in an eelgrass bed

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 Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 424: [87][88][89][90][91][92][93][94][95] 2011 Despite the ecological and environmental importance of eelgrass beds, their decline has been observed in many areas of the world, i.e. Florida Bay in North America (Fourqurean & Robblee 1999), Japan (Environment Agency of Japan 2000), the European Mediterranean (Marbà et al. 2005), and Australia (Walker et al. 2006). Over the last decade, 90 000 ha of eelgrass loss has been documented, although the actual area lost is certainly greater (Short & WyllieEcheverria 1996). Declines have been attributed to (1) disturbance of coastal and estuarine environments, including industrial, residential, and recreational development, where impacts are most notably manifested in the near-absence of eelgrasses in industrialized ports and areas of intense human coastal development (Short & Wyllie-Echeverria 1996, Orth et al. 2006, and (2) the incursion of non-native species (Orth et al. 2006, Martínez-Lüscher & Holmer 2010.We found the non-native seaweed Sargassum muticum (Yendo) Fensholt (Phaeophyceae: Fucales) colonizing an eelgrass bed at the head of Bamfield Inlet, Bamfield, British Columbia. A non-native seaweed from southeast Asia, Sargassum muticum was accidentally introduced to British Columbia around the 1940s with Japanese oysters Crassostrea gigas that were imported for aquaculture (Scagel 1956). Sargassum muticum is both a fouling species and an opportunist (Critchley...

Anthropogenic structures and the infiltration of natural benthos by invasive ascidians

“…Interestingly, when B. violaceus and B. schlosseri were recorded on rocky reefs in our field surveys, they often occurred as epibionts on algae, particularly on the fronds of non‐native Sargassum muticum . Their ability to utilize secondary substrata, such as algal fronds, as habitat may help facilitate their infiltration into natural benthos (White & Orr 2011).…”