We investigated the roles of facultative versus strict niche feeding in the maintenance of trophic consistency in soft-bottom macrobenthic communities in the Strait of Georgia, British Columbia, Canada. Changes in trophic structure across gradients in depth and percent fine sediments were examined over a broad regional scale by identifying trophic compartment(s) responsible for the resulting trophic changes. The use of proportional organic biomass data allows direct comparison of community trophic structure across diverse hydrographic regime(s), large ranges in overall biomass and productivity, and highly variable community composition. Cluster analyses revealed low overall dissimilarity in trophic structure across all substrate and depth ranges (24 and 28% divergence, respectively), suggesting an overall economy of trophic function. Similarity percentage (SIMPER) analyses revealed that low trophic dissimilarity is driven primarily by the remarkably even distribution of the 2 dominant facultative feeding groups in all habitat types. These facultative groups contained the most ubiquitous and abundant taxa found throughout the Strait, and likely confer strong resilience in these communities to habitat change. In contrast, the small but significant divergences in trophic structure over depth and percent fine sediment gradients was explained by the distributions of strict niche feeders: (1) macro-omnivores and herbivores dependent on non-detrital food sources were important in shallow areas (< 25 m) with coarse sediments (<10% fine sediment), contributing to a unique trophic composition in these areas; and (2) subsurface deposit feeders were the only trophic group to vary significantly in proportional biomass explained by depth and percent fine sediment combined (22%; positive linear response to both factors).KEY WORDS: Deposit feeding · Suspension feeding · Strait of Georgia · Salish Sea · British Columbia · Facultative feeding · Trophic structure Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 445: [129][130][131][132][133][134][135][136][137][138][139][140] 2012 2001). Most studies of macrobenthic trophic structure tend to classify benthic fauna in terms of strictly defined trophic groups only (e.g. Chardy & Clavier 1988, Gaston & Nasci 1988, Ricciardi & Bourget 1999, García-Arberas & Rallo 2002, Coyle et al. 2007, Albano & Obenat 2009, Cacabelos et al. 2009, Dolbeth et al. 2009). Most commonly these trophic groups are: suspension feeders, deposit feeders (surface and subsurface), carnivores, herbivores and omnivores. However, many macrobenthic taxa exhibit more than one feeding mode (e.g. Okamura 1990, Brown et al. 2000, Gaudencio & Cabral 2007, Gray & Elliott 2009). This trophic flexibility has been proposed as an important feature of benthic marine communities (Cadée 1984). For instance, many species of facultatively carnivorous polychaetes are also known to deposit feed (e.g. Glyceridae, members of Lumbrineridae; Fauchald & Jumars 1979). Other taxa ...

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