Additive partitioning of estuarine benthic macroinvertebrate diversity across multiple spatial scales

Knowledge of how diversity changes across spatial scales is important for conservation of biodiversity. Alpha (alpha), beta (beta) and gamma (gamma) species richness and Shannon-Wiener diversity index (H') of benthic macroinvertebrates were analysed by additive partitioning across 3 different nested spatial scales (cm, m and km scales) in the estuarine Baltic Sea-North Sea transition area. The data set consisted of abundance of 324 species from a total of 638 samples taken at 64 sites distributed over 6 salinity-defined regions. Results were compared to a null model, randomly assigning individuals of species among samples beta-richness among regions was significantly high and the major contributor to gamma-richness, while alpha- and beta-richness were less than expected at finer scales, Suggesting that salinity-defined regions largely determined gamma-richness. Salinity effects on alpha-richness were positive and most evident at a regional scale, likely reflecting differential evolutionary adaptation to salinity among species. For H', the greatest. contribution to gamma-diversity was from alpha and beta at the finest scale, but significantly high contributions at larger scales likely indicated that different species dominated abundance in different sites and regions. Effects of rare species on partitioning of total richness was less different from random, compared to common species, for beta among regions, suggesting that the occurrence of rare species was more affected by chance than for common species, Results suggest that additive partitioning is a simple and effective tool to unravel changes and sources in diversity over spatial scales in marine and/or estuarine benthic environments. This method may be used to assess effects of habitat homogenisation and as a basis for the design of conservation protocols.