Effect of background substrate on recruitment of benthic marine invertebrates to subtidal cobble-filled collectors

The availability of suitable substrate for settlement can alter the behaviour of larvae of benthic marine invertebrates and consequently their settlement patterns. We tested the effect of the background substrate of a site (rocky vs sediment) on recruitment of invertebrates settling into standardized cobble-filled collectors deployed at shallow subtidal sites in the south-western Bay of Fundy, Canada, in 2009 and 2010. The assemblage of invertebrates that settled into the collectors differed significantly in both abundance and species composition between “paired sites” (≈0.003–0.009 km2 in area and 345–861 m apart) with rocky vs sediment background substrate, and markedly less so between paired sites comprised of rocky bottom. Species that are known to be rock-dwelling recruited in greater abundance to cobble-filled collectors at rocky sites, while those known to be sediment-dwelling recruited more to cobble-filled collectors at sediment sites. At the smaller spatial scale of patches of sediment within one site (14–107 m apart), differences in abundance but not species composition were detected between collectors on the two types of background substrate. This study supports the idea that larvae of some species of marine invertebrates respond to substrate at a larger spatial scale than their immediate location of settlement.