Abstract
The large-scale distribution pattern of megafauna communities along the Mediterranean middle slope was explored. The study was conducted between 500 and 800 m depth where deep-water fishery occurs. Although community studies carried out deeper than 500 m are partly available for some geographic areas, few large-scale comparative studies have been carried out. Within the framework of the MEDITS survey programme, we compared the megafauna community structure in ten geographical sub-areas (GSAs) along the Mediterranean coasts. Additionally, the spatial distribution of fishing was analysed using vessel monitoring by satellite information. Overall, the community showed a significant difference between sub-areas, with a decreasing eastward pattern in abundance and biomass. Longitude was the main factor explaining variation among sub-areas (by generalized additive models). However, we found a region which did not follow the general pattern. GSA 6 (northern Spain) showed significantly lower abundance and a different composition structure to the adjacent areas. The decrease in community descriptors (i.e. abundance and biomass) in this area is probably a symptom of population changes induced by intense fishery exploitation. Overall, a combination of environmental variables and human-induced impacts appears to influence the bentho-pelagic communities along the slope areas of the Mediterranean.
Highlights
The continental slopes are the connecting habitat between the shelf (200 m) and the deep basins (4000 m)
The study covers ten geographical sub-areas (GSAs) with specific environmental and biological characteristics defined by the General Fisheries Commission for the Mediterranean (GFCM): the northern Alboran Sea (GSA 1), Alboran Island (GSA2), the Balearic Islands (GSA 5), northern Spain (GSA 6), the Gulf of Lions (GSA 7), eastern Corsica (GSA 8), the central-southern Tyrrhenian Sea (GSA10), the Strait of Sicily (GSA 16), the southern Adriatic Sea (GSA 18) and the western Ionian Sea (GSA 19)
In GSA 6 other Mollusca represent more than 50% of the community
Summary
The continental slopes are the connecting habitat between the shelf (200 m) and the deep basins (4000 m) They play an important role in the global carbon cycle, cycling nutrient and providing valuable food and energy resources (Levin and Dayton 2009). These biological systems cannot support high levels of exploitation due to their low productivity and the presence of productive but not yet well-identified habitats (de Juan and Lleonart 2010, Norse et al 2012, Watson and Morato 2013). The biological production decreases from north to south and west to east and is inversely related to the increase in temperature and salinity, being the eastern basin one of the poorest marine areas in the world (Azov 1991, Danovaro et al 2010)
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