Spatial variation in biodiversity patterns of neuston in the Western Mediterranean and Southern Adriatic Seas

Neuston - comprising a diverse assemblage of organisms living in the surface layer of the water column - plays a unique ecological role in marine life. Notwithstanding its importance, quantitative information on its spatial structure are still limited, in particular for the Mediterranean Sea. Here, the spatial structure of neuston assemblage of the Western Mediterranean and the Southern Adriatic Seas was analysed, with particular emphasis on the biodiversity pattern in the two study areas. A total of 59 stations were sampled in an oceanographic cruise conducted in May-June 2013. Additional analyses were performed on data on 21 stations sampled in the Southern Adriatic in March 2015 in order to confirm the generality of the patterns observed in the 2013 cruise. Geostatistical analyses indicated that in 2013 in the Southern Adriatic the variation in taxonomic richness, abundance, and ecological diversity of the neuston across stations was characterized by a significant spatial autocorrelation. Conversely, in the Western Mediterranean a negligible spatial structure was observed. In addition, the taxonomic richness and ecological diversity of the neuston resulted significantly higher in Southern Adriatic than in the Western Mediterranean. Data collected in the 2015 cruise confirmed a high taxonomic richness and diversity for the Southern Adriatic; furthermore, a significant spatial autocorrelation was observed for both parameters. The present study represents an original insight into the structure of the neuston community in the Mediterranean Sea, providing strong evidence of the spatial variability of its diversity patterns. The influence of local and large-scale processes is discussed, and the need of more extended investigations is emphasized.