Spatial variation in the recruitment of benthic assemblages to artificial substrata

Artificial substrata have repeatedly been advocated as useful tools for monitoring environmental change; however, the spatial scales of recruitment to these substrata are mostly unknown. Nests of nylon pan scourers were used to examine variation in the recruitment of marine benthic assemblages over a range of spatial scales (metres, 10s of metres, 100s of metres, kilometres), within the Solitary Islands Marine Park (SIMP), NSW, Australia. Using a nested design, artificial substratum units (ASUs) were anchored to rocky reef for a period of 5 mo, at a depth of 6 to 8 m, at 2 island sites. Data were subjected to both univariate and multivariate analyses to determine the similarity of assemblages between all hierarchical levels. Artificial substrata were colonised predominantly by motile fauna. Large-scale patterns of recruitment were obvious, with samples from NW Solitary Island numerically dominated by the bivalve Hiatella australis, and samples from North Solitary Island by the amphipod Mallacoota euroka. Significant differences in the mean abundance of individual faunal groups (amphipods, bivalves, polychaetes, decapods) were identified over all spatial scales. Multivariate analyses revealed the structure of recruiting assemblages varied over all scales although differences at the smallest spatial scale were uncommon. The results highlight the importance of variation over both small and large spatial scales for assemblages of motile fauna recruiting to artificial substrata, and suggest that this variation needs to be considered when conductingexperiments with these types of artificial substrata.