The Western Mediterranean sea covers an area of approximately 0.9 million km2 in subtemperate to temperate latitudes (36° to 46° N, approximately). It is connected to the North Atlantic Sea through the 14 km-wide straits of Gibraltar and is characterised by narrow continental shelves, where biological productivity and consequently fisheries are concentrated. Temperatures are relatively high, with high salinity and oxygen levels but, in comparison to the adjacent North Atlantic, it is considered to be low in nutrients and plant life and rich in oxygen. Biological productivity is generally low with zones of high primary production restricted to areas of high fresh water runoff near rivers or in coastal lagoons where there exists a risk of eutrophication (for further information see Land-based pollution).
The Western Mediterranean has a high biological diversity, with 87% of all Mediterranean species occurring in the western basin, including charismatic species such as dolphins, turtles and seabirds. Various conservation and regulatory instruments exist to safeguard these ecologically important species and marine habitats, but nature conservation is often subordinate to the competing demands of the region’s 150 million residents and 200 million annual tourists.
The Western Mediterranean coastal zone is increasingly under threat from climate and non-climate stressors, such as human uses. The most important key drivers, which are having impacts on coastal systems in the Western Mediterranean, were identified during VECTORS as: tourism, fisheries, maritime transport, energy, and extraction and disposal activities. The first three were examined using a variety of observational techniques as well as state of the art knowledge and modelling approaches.
Tourism accounts for 68% of the total economic value of the Western Mediterranean coastal systems and 20-30% of the world’s tourists visit the area. Tourism provides economic benefits to local (and national) economies but tourism-related activities impose a high demand on the goods and services provided by coastal systems (energy, clean water, space, etc.). Touristic development combined with increasing coastal populations have led to degradation and habitat loss in areas such as lagoons, deltas, estuaries and seagrass meadows.
The increasing exploitation of living marine resources by fisheries in recent decades has led to 80% of fish stocks being exploited beyond safety limits. This has impacts beyond the populations of target species and has led to changes in marine food webs, has likely increased jellyfish numbers and bloom frequency, and has reduced marine biodiversity. In particular, bottom trawling negatively affects the structure and function of seabed communities. These impacts may be exacerbated by climate change, and may facilitate the spread of invasive species.
Different types of research methodologies were applied to increase scientific understanding of the dynamics of human impacts and how they relate to, and are affected by, socio-economic pressures.
The work that has been done in the Western Mediterranean has focused on gaining a mechanistic understanding of how pressures, specifically relevant in the Western Mediterranean, cause changes in ecosystem functioning, biodiversity, ecosystem goods and services and economic activities.