Biodiversity and dispersal of demersal community in the Central Mediterranean Sea

It is well known that the major groups of animals and plants increase the gradient of diversity from the poles to the tropic. Patterns of marine biodiversity may not conform to the terrestrial model, because the spectrum of environmental variation in the sea has a longer wavelength over both ecological and evolutionary time scales than on land (Gee et al., 1996). In this contest the impact of exploitation on demersal resource and on fish diversity in the Central Mediterranean Sea becomes a relevant question. In all the Mediterranean demersal resources are exploited both by trawler fleet and by numerous small fishing vessels using various gear, such as trammel nets, gillnets, longline etc. It seemsmost likely that the changes in fish community structure can be related to the destruction of large epibenthic organisms by the trawl gear. Fishing affects demersal fish communities through selective removal of target species, by-catch of non-target species and habitat modification, resulting in changes in overall biomass, in species composition and size structure (Bianchi et al., 2000). Documented changes in the structure of demersal fish communities include: Pauly (1979); Gulland and Garcia (1984); Greenstreet and Hall (1996); Sharp and Csirke (1984); Sainsbury et al. (1997); Haedrich and Barnes (1997); Bianchi et al. (2000). In this paper we focus our study on changes in species diversity, between seven area, and dispersal of marine organisms in the Central Mediterranean Sea.