Structure and functioning of Mediterranean lagoon fish assemblages: a key for the identification for water body types

Knowledge on the structure and functioning variability of transitional water fish assemblages may help in finding out the main descriptors for identifying different water body types for which specific biological reference conditions can be reliably derived. Fish assemblages from 19 Mediterranean lagoons were therefore investigated by evaluating the variability of their structure and functioning, and by relating it to the lagoons’ environmental features. Fish assemblage structure was measured by its species richness. Functioning was measured by categorizing fish species into functional categories (or guilds) according to their use of lagoon habitat, feeding and reproduction, and by defining the functional structure of fish assemblages as the relative number of species per guild in each lagoon. Mediterranean lagoons’ fish assemblages were found to be more similar to each other in their functional structure than in the taxonomical composition, thus confirming a shared functional role of these environments for biological communities. Lagoon local features, such as the lagoon area, its habitat heterogeneity and average salinity, significantly affected the total species richness and the different use that fish make of the lagoon environment, hence playing a primary role in the assessment of these water body types. Latitude also influenced the variability of fish assemblages in the Mediterranean lagoons investigated, with particular regard to their functioning as feeding and reproductive grounds for fish. These results are compared with previous studies and, although this limited the investigation to structural aspects only, were found to confirm in part the previous results and also added new insights about the key factors affecting the functioning of transitional water systems.