Hydrological constraints to macrobenthic fauna biodiversity in transitional waters ecosystems

Lagoons are habitat islands in the coastal landscapes characterised by heterogeneity among ecosystems, due to the different terrestrial-freshwater-marine interfaces, as well as by heterogeneity within an ecosystem, due to an intrinsic patchy spatial distribution of abiotic and biotic components. Here, we investigated the influence of nine hydrological forcing factors of the patchiness of a lagoon benthic macroinvertebrates, described through macroinvertebrate diversity. This study is based on the analysis of two databases built, respectively, upon (1) a literature survey (ITA-DB) carried out considering a 25-year period and (2) a series of sampling campaigns during 2004-2005 in ten Mediterranean and Black sea lagoons (CaD-DB). Both databases showed a patchy distribution of macroinvertebrate taxa among lagoons with most taxa found in one or two lagoons only. Average similarity in taxa composition among lagoons revealed to be low for both ITA-DB (10%) and CaD-DB (11%), showing that macroinvertebrate taxonomic diversity is strictly linked to large-scale phenomena. Regression trees models indicate that 60.0% (ITA-DB) and 42.3% (CaD-DB), respectively, of total deviance of the macroinvertebrates diversity are explained by physiographical and hydrological factors, being openness and tidal range the two most relevant components. Therefore, hydrological constraints in the connection between lagoon and marine ecosystems seem to have a relevant role in the organisation and maintenance of benthic macroinvertebrate fauna of coastal lagoons. In order to design strategies of biodiversity conservation in Mediterranean transitional waters one suggested direction is a coordinated, inter-country governance, rather than a purely local management.