Spatial scaling in the distribution of macrofauna associated with Sargassum stenophyllum (Mertens) Martius: analyses of faunal groups, gammarid life habits, and assemblage structure

Abstract

Benthic communities can vary greatly at a range of temporal and spatial scales, due to different ecological processes that operate at each scale. Characteristics of the natural history of the organisms, such as mobility and behavior, can influence their distribution, mainly at smaller scales. In this study, the spatial distribution of the macrofauna associated with Sargassum stenophyllum in SE Brazil was documented using a hierarchical sampling design, repeated four times throughout 1 year. We found differences in the density of the main macrofaunal groups at spatial scales ranging from meters to kilometers, sometimes with greater differences at smaller scales than between shores. We then analysed whether life habits influenced the distribution of gammarid amphipods, the dominant group. The distribution of tube-building amphipods was generally more patchy than that of free-living animals, although some variation among species was found within each category. Multivariate analyses indicated distinct gammarid assemblages a few meters distance from each other. Similarity among assemblages was reduced when comparing more distant assemblages, whereas faunal density influenced similarity in one of the four sampling dates. Factors that may influence the small-scale patchiness found in phytal communities include differences in physical conditions created by the spatial distribution of the substrate, habitat complexity as a result of epiphyte colonization, and aggregations caused by colonization of algal patches by organisms with direct development. Differences in reproductive and dispersal strategies of the animals can influence small-scale distribution of these assemblages, suggesting that effective descriptions of phytal communities should include more than one spatial scale.