Resource specialisation among suspension-feeding invertebrates on rock walls in Fiordland, New Zealand, is driven by water column structure and feeding mode

Abstract

Sessile suspension feeders are an important component of benthic-pelagic coupling on subtidal rocky reefs. We used stable isotope analysis to investigate intra-specific variation in trophic level and composition of basal organic matter sources (macroalgae and phytoplankton) supporting food webs used by sessile suspension feeders from rock wall sites throughout Fiordland in southwestern New Zealand. We characterised water column structure in terms of salinity and chlorophyll a from a 12 yr time series of CTD casts at 25 sites. During 2006 and 2010, at these same 25 sites, we measured the depth distribution of 8 common sessile suspensionfeeding inverte brates that use a broad range of feeding modes. In order to resolve variability in the use of basal organic matter sources in the food webs supporting these species, we measured δ 13C and δ 15N of the 8 suspension-feeding species at 11 core sites. Using a mass balance approach, we assessed intra-specific variability in the composition of basal organic matter as well as the trophic level of each species. These data demonstrate distinct patterns of resource specialisation among species linked to depth distribution and to intra-specific variation in food web position. Our results indicate that species composition and depth distribution of benthic suspension feeders have important influences on benthic-pelagic coupling at the regional scale (100 to 300 km). © Inter-Research 2012.