Habitat isolation and size influence the structure of macroinvertebrate benthic assemblages

Abstract

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The structure of local communities is generally thought to be the result of local responses to environmental and biotic factors. Recent theoretical advances have, however, emphasized the role of dispersal in structuring communities. In this study we examined the effects of habitat isolation and habitat size in structuring macroinvertebrate benthic assemblages. We manipulated distance to a rocky reef (as a surrogate to isolation from a source of colonists) and habitat size of experimental mimics of macroalgal turfs. Experimental habitats were deployed following a hierarchical structure in which experimental patches were grouped in small (3 patches) and large (6 patches) habitat groups (referred to as metacommunities). Our results show that isolation influenced the richness of sessile organisms, with greater numbers of species closer to the reef, regardless of the scale at which diversity was measured (i.e. metacommunity or patch scale). In contrast, motile richness did not respond to habitat isolation. Sessile richness was similar in small and large metacommunities, whereas motile richness was greater in large metacommunities, but only at the scale of the patch. Species composition in isolated habitats was similar (for sessile) or a subset (for motile) of that found closer to the reef suggesting that differences in richness were associated with the ability of species to disperse and not to different environmental conditions between isolated and non-isolated habitats. Despite spatial variability in assemblages, results were spatially consistent. Overall, our results indicate that species dispersal ability mediates the effects of isolation and habitat size and that results are scale-dependent.

Keywords

• macroinvertebrates
• scale
• richness
• Artificial habitats
• Species movement