Fish-seaweed association on temperate reefs: do small-scale experiments predict large-scale patterns?

Abstract

Processes affecting reef fish populations are likely to vary with spatial scale, but there have been few attempts to determine whether predictions generated by small-scale experiments are manifested at larger spatial scales. Our goal in this study was to determine if patterns of microhabitat use measured in small-scale experimental manipulations scaled-up and allowed predictions of among-reef patterns of abundance across larger spatial scales. Manipulations of algal biomass in artificially created 1.5 m 2 plots indicated that patches of Sargassum filipendula supported greater numbers of slippery dick Halichoeres bivittatus than those with an equal biomass of Zonaria tournefortii, or than patches with an equal mix of S. filipendula and Z. tournefortii. Scaling up and manipulating S. filipendula and Z. tournefortii abundance in 100 m 2 sections of reef produced results qualitatively similar to the small-scale experiments; fish densities varied as a function of S. filipendula mass. Larger scale surveys of fish densities and algal biomass on large reefs separated by 1 to 30 km showed positive associations between fish density and S. filipendula biomass. For the reefs that we studied, our small-scale experiments scaled up and predicted large-scale patterns of abundance on reefs in the South Atlantic Bight.