ORIGINAL ARTICLE Phylogeography of Acesta clams from submarine seamounts and escarpments along the western margin of North America Gillian E. Clague 1 , William Joe Jones 2 , Jennifer B. Paduan 1 , David A. Clague 1 & Robert C. Vrijenhoek 1 1 Monterey Bay Aquarium Research Institute, Moss Landing, CA, USA 2 Environmental Genomics Core Facility, University of South Carolina, Columbia, SC, USA Introduction The slow-growing animals that dominate many submar- ine seamounts are especially vulnerable to habitat damage that accompanies trawling for deep-sea fisheries (e.g. Koslow et al. 2001). Trawling dramatically reduces popu- lations of large sessile suspension-feeders such as corals and sponges and thereby affects the structural complexity and diversity of benthic communities (Althaus et al. 2009; Clark & Rowden 2009). Despite conservation efforts, recovery of these assemblages is hampered by slow recruitment. Seamounts are believed to share many characteristics with other oceanic islands, i.e. geographical isolation, high endemicity and accelerated rates of specia- tion (Hubbs 1959; Wilson & Kaufmann 1987; Richer de Forges et al. 2000). Nonetheless, recent surveys indicate that seamount communities may not be as distinct from neighboring deep-sea regions as previously suspected, suggesting that significant undersampling and taxonomic uncertainties may partly be responsible for previously reported patterns of isolation and endemicity (Samadi et al. 2006; McClain 2007; O’Hara 2007; McClain et al. 2009; Thoma et al. 2009; Clark et al. 2010). The present study emerged as a side project from ongo- ing geological and biodiversity surveys of seamounts bor- dering the Eastern Pacific margin of North America, Keywords Acesta; connectivity; mitochondrial cytochrome oxidase subunit I (COI ); phylogeography; seamounts. Correspondence Robert C. Vrijenhoek, Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, USA. E-mail: vrijen@mbari.org Accepted: 11 April 2011 doi:10.1111/j.1439-0485.2011.00458.x Abstract Genetic connectivity and habitat characteristics were examined in two species of Acesta clams (Bivalvia: Limidae) from submarine seamounts and continental slopes along the western North America margin. Two species were identified from dive videos obtained with submarine remotely operated vehicles that sur- veyed a 2200-km range between 27° and 46° N latitude. Acesta sphoni was only found at shallower habitats (545–860 m depth) in the southern part of this range, whereas Acesta mori was more abundant and widely distributed in deeper habitats (1029–1996 m). Both species occurred on seamounts and on the walls of submarine canyons and continental slopes. Segregation of these species by depth exposes them to correlated differences in water temperatures and dissolved oxygen concentrations. Ninety-eight individuals sampled from seven seamounts and one escarpment locality were characterized with DNA-barcodes based on 643 base pairs of mitochondrial cytochrome-c-oxidase subunit I (COI). Further analysis of these sequences revealed no significant geographical subdivision across the sampled range. This lack of differentiation suggests ongoing genetic exchange between the seamount populations and those possibly distributed along the continental margins. Examination of regio- nal bathymetric profiles suggested that an abundance of suitable habitat might exist along these margins. Marine Ecology. ISSN 0173-9565 Marine Ecology 33 (2012) 75–87 ª 2011 Blackwell Verlag GmbH 75