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The same authors proposed a plan of action to address the conservation issues and management
of human activities related to the protection of the Mediterranean deep seas, framed within the
current relevant legal situation, and considering the international policy context and the current
commitments to the relevant international conventions.

2.3.3 Biodiversity of the Mediterranean High Seas

While it exhibits a low overall level of biological productivity, the Mediterranean Sea as well as the
surrounding lands is characterized by a relatively high degree of biological diversity (UNEP 1999).
The fauna includes many endemic species and is considered richer than that of Atlantic coastal
areas (Bianchi and Morri 2000). With few exceptions, the continental shelf is usually narrow, but
the coastal marine area of the Mediterranean, which stretches from the shore to the outer extent of
this continental shelf, shelters rich ecosystems and the main areas of high productivity in the sea.
Whereas central zones of the Mediterranean are generally low in nutrients, coastal zones benefit
from telluric nutrients that support higher levels of productivity.

The biota of the Mediterranean Sea consists primarily of Atlanto-Mediterranean species (62%)
derived from the adjacent Atlantic biogeographic provinces beyond the Strait of Gibraltar. Many
(>20%) Mediterranean species are endemic, while others are cosmopolitan or circumtropical
(13%), or Indo-Pacific (5%). These proportions differ for different major taxonomic groups and also
for different parts of the Mediterranean Sea, but the pattern remains essentially the same
(Ketchum 1983).

Within the Mediterranean there is a gradient of decreasing species diversity from west to east. The
number of species among all major groups of plants and animals is lower in the eastern
Mediterranean than in the western and central parts of the sea. The southeast corner, the Levant
Basin, is the most impoverished area. The benthic and littoral populations show a similar change in
species diversity and abundance, which decrease from west to east, and from the northern Adriatic
to the south (Ketchum 1983).

According to Zenetos et al. (2005), out of a total of about 6000 benthic invertebrate species in the
Mediterranean, about 67% (4030) are found in the Western Mediterranean, 38% (2262) in the
Adriatic Sea, 35% (2119) in the Central Mediterranean, 44% (2637) in the Aegean Sea, and 28%
(1658) in the Levantine Sea. This trend in number of species demonstrates a west-east
zoogeocline: a large number of geographic, climatic and trophic variables are highly correlated with
this pattern which has been found to be similar for many taxonomic groups (Zenetos et al. 2005).

This zoogeocline is also evident from a map (Fig. 2-8), available from the online project
“AquaMaps” (www.aquamaps.org, Kaschner et al. 2008), representing the species-richness
distribution of 79 deep sea fish species. AquaMaps is an approach to generating model-based,
large-scale predictions of currently known natural occurrence of marine species. Models are
constructed from estimates of the environmental tolerance of a given species with respect to depth,
salinity, temperature, primary productivity, and its association with sea ice or coastal areas. Maps
show the colour-coded relative likelihood of a species to occur in a global grid of half-degree
latitude / longitude cell dimensions, which corresponds to a side length of about 50 km near the
equator. Predictions are generated by matching habitat usage of species, termed environmental