Relative importance of local biotic and environmental factors versus regional factors in driving macrobenthic species richness in intertidal areas

Species richness depends on both regional and local factors, including regional species pools and habitat type.We compared diversity, scaling from α (site species richness) to β (heterogeneity in species richness) and γ (location species richness), at 6 different intertidal habitat types within 8 coastal locations in the New Zealand North Island.Physical variables at each location (the harbour total area to high water, tidal prism and % intertidal) and habitat variables (comprising habitat fragmentation indices and number and size of patches) were correlated with the diversity measures, evaluating the importance of local variables against regional species pools.Results showed that differences in diversity indices within locations were greater than between locations, and that generally habitats with structuring fauna (cockles, seagrass, tubeworms) held higher diversity than purely sedimentary habitats (mud and sand).In all habitats except mud, local variables had significant interaction with diversity; patch size had a positive effect for all diversity measures, and fragmentation indices had negative effects.The intertidal extent also negatively affected diversity, especially regional species richness.These findings underline the importance of minimising habitat loss and fragmentation for the conservation of marine soft sediments.