Relationships between mobile macroinvertebrates and reef structure in a temperate marine reserve

Relationships between different metrics of reef structure and the density of macroinvertebrates were examined at 3 nested spatial scales inside and outside a long-established, 'no-take' marine protected area (MPA) at Maria Island, Tasmania, Australia. Generalized linear models were developed that best explained the contributions of rugosity, substratum composition (different-sized boulders, bedrock, sand) and refuge metrics to the spatial variability in invertebrate species richness, total abundance, and the abundances of major taxonomic classes and focal species. To distinguish responses associated with protection from fishing from those relating to natural geographic variation, relationships between reef structure and invertebrate density were also assessed using survey data from before the MPA came into effect. Models combining reef structure and MPA protection explained between 44 to 67% of spatial variability of total invertebrate abundance across all survey scales examined (1 x 5, 1 x 50 and 1 x 200 m). The number of refuge size categories provided the best predictor of invertebrate species richness at the 5 m scale; however, no reef structure metric investigated was significant at the largest (200 m) spatial scale for species richness. Amongst the explanatory variables examined, MPA protection and density of small refuges generated significant responses for the majority of taxa. One commonly applied metric of reef structure, rugosity, was found to be a relatively poor predictor of invertebrate abundance and richness, generating few significant relationships. Comparisons with pre-MPA data indicated that protection from fishing greatly influenced most major components of the invertebrate community, while reef structure appears to have little interactive influence on these MPA effects at the scales tested here.