Hierarchical scaling of biodiversity in lagoon ecosystems

Lagoons are habitat islands in the coastal landscapes characterised by both among ecosystems heterogeneity, due to different terrestrial-freshwater, freshwater-marine interfaces, and within ecosystem heterogeneity, due patchy spatial and temporal distribution of biotic and abiotic components. Here, we investigate to what extent biodiversity in lagoon ecosystem is affected by these different sources of heterogeneity and which are the implications of the different sources for biodiversity management at the local scale of each single lagoon. To this aim, we focused on benthic macroinvertebrates using two sources of data: literature data on a sample of 26 Italian lagoons, and synoptically collected data on a sample of 10 lagoons in Eastern Mediterranean and Black Sea. The first data set allowed interface on the among ecosystem heterogeneity and the second on the within ecosystem heterogeneity at the scale of habitat type. Therefore, a hierarchical scaling of biodiversity in lagoon ecosystem is globally addressed. Results show that the largest component of biodiversity in lagoon ecosystems is due to the differences among ecosystems. Dissimilarity among the taxonomic composition of macro-invertebrate guilds of the Italian lagoons was close to 90%. Differences in habitat type within lagoon ecosystems also affect biodiversity but less than among ecosystem differences; average dissimilarity among habitat types at the ecosystem level was 66.4±10.6 and within habitat types 49.67±6.0. The analysis suggest that most of biodiversity on benthic macro-invertebrates guilds in the Mediterranean and Black Sea is maintained at Ecoregional scale, being realised only at a small extent at every local ecosystems. This finding stress the importance of a transnational governance of coastal ecosystem health in order to preserve biodiversity at any local scale within the EcoRegion. A role of land use management in lagoon watersheds was also emphasised and scaled up with respect to biological interactions acting at very local scale.