Scales of spatial variation in tropical benthic assemblages and their ecological relevance: epibionts on Caribbean mangrove roots as a model system

The analysis of spatial patterns of biodiversity remains a focal issue in ecological studies. The recognition of spatial scales at which significant differences in biodiversity are detected allows us to infer the relative importance of the ecological processes that may shape those patterns. In marine benthic studies, small-scale variability is always seen, irrespective of habitat, but little consensus exists on the relative importance of variability at intermediate and wider spatial scales, and thus the drivers acting at each of those scales. In this study, the relevance of different spatial scales for fouling assemblages on the roots of the Caribbean red mangrove Rhizophora mangle L. was assessed by partitioning variation in richness and species composition over 4 natural and nested spatial scales observed on 5 occasions. Spatial scales consisted of 2 marine parks (about 400 km apart), sectors representing environmental gradients (1-2 km apart), sites within each sector (50-400 m apart), and neighbouring roots (1-2 m apart). Species richness and species composition varied significantly at all spatial scales. The greatest partitioned variation for richness was among parks, followed by neighbouring roots, whereas the opposite pattern was found for species composition. The relative magnitude of sector and site variability depended on the park, for both species richness and composition. These results highlight the importance of processes that operate at the scales of 100s of kilometres and a few metres over local drivers such as environmental gradients and the dispersal abilities of larvae.