Single large or several small marine reserves? An experimental approach with seagrass fauna

On of the most frequently debated theories in conservation biology is whether a Single Large area will preserve more species than Several Small areas of the same total area (the SLOSS debate). We tested this theory in the marine environment by comparing the diversity and abundance of fish and macroinvertebrates associated with small and large seagrass beds. In natural beds, several small beds had significantly more species than a single large bed. This occurred because a large proportion of species were not shared among beds. However, results of experiments using artificial seagrass beds to manipulate size of beds were equivocal. More species and more individuals were found in several small beds on only few occasions in experimental treatments. These results contradicted the patterns found in comparisons among natural beds. Our results stress the need to experimentally validate theories for reserve design and also indicate the danger of directly applying land-based principles to marine communities without critically examining them for each habitat.