Habitat configuration affects colonisation of epifauna in a marine algal bed

Habitat fragmentation is a threat to the preservation of both terrestrial and marine biodiversity. While terrestrial systems have been well studied, relatively few studies have considered how changes to the spatial arrangement of habitats affect fauna in marine systems. In this study, sampling and manipulative experiments examined the effects of varying the size and isolation of habitat patches on the abundance of mobile invertebrates inhabiting an algal dominated rocky reef. Variation in the size of naturally occurring patches of the brown alga Sargassum linearifolium did not impact upon the abundance of any taxonomic groups, with the exception of polychaete worms, which were most abundant in small patches. When habitat patch size and isolation were manipulated, the abundance of colonising isopods increased with increasing isolation from contiguous habitat. Amphipods and ostracods colonised small patches to greater numbers than large patches. Sampling of the matrix was undertaken to examine the rarely tested assumption that the area between habitat patches is not a potential source of colonists to the habitat in question. The matrix was found to support a strikingly different community of invertebrates than did the algal habitats and thus was unlikely to be a source of colonists to isolated algal patches. The increased abundance on small and isolated patches for some taxa are inconsistent with traditional predictions of the effects of reduced habitat patch sizes and indicate that patchy landscapes should not necessarily be considered poor habitats. The variation in responses among taxonomic groups suggests that a range of patch sizes may be necessary to maintain species diversity.