In a new study, just published in the online free journal PLoS ONE *, Marta Coll and 36 co-authors, experts of the Mediterranean Sea, have joined forces to update the estimates of how many marine species inhabit the Mediterranean Sea, using the information available in the published record and the opinion of experts. Based on this information, they also described the overall spatial distribution of these species and how they have changed with time, in addition to identifying the major threats to biodiversity.

The results list approximately 17,000 marine species occurring in the Mediterranean Sea, which highlights that the Mediterranean Sea is a region with a high biodiversity. The study contains an extent appendix which includes revised lists of several taxonomic groups. This is an important new information that is freely available as well *.

One will note that these new estimates of marine diversity are still incomplete as there are many species that are still unknown to science. For example, the diversity for the smallest organisms, such as microbes, is substantially underestimated, and the deep-sea areas - particularly in the southern and eastern Mediterranean region - remain poorly known. The study also confirms that the invasion of alien species (currently more than 600 species) is an important factor. Many invasive species, of tropical origin, are recorded in the eastern basin (see CIESM Atlases of Exotic Species for details) and they can spread to the west due to the warming of the Mediterranean Sea.

The spatial patterns that were analyzed show a general decrease in biodiversity from the northwestern areas to southeastern regions. This pattern follows the known gradient of production that has been described in the Mediterranean Sea. However, the authors caution that there are still enormous gaps in the knowledge of the organism inhabiting the Mediterranean Sea along the southern and eastern regions. The results also show that marine biodiversity is generally higher in coastal areas and continental shelves, and decreases with depth.

The results of this study suggest as well that overexploitation of marine resources and the habitat loss have been the main human drivers of changes in biodiversity of the Mediterranean Sea during the past. Nowadays, habitat loss and degradation, followed by fishing impacts, pollution, climate change, eutrophication, and the establishment of alien species are the most important threats and affect the greatest number of organisms. Scientists think that all these impacts will likely grow in importance in the future, along with climate change and habitat degradation.

Finally, this study identifies the hot spots, or areas of conservation concern, where several endangered, threatened, or vulnerable species concentrate. These areas concern most of the western Mediterranean shelves (and in particular, the Strait of Gibraltar and the adjacent Alboran Sea), the North African coast, the Adriatic, and the Aegean Sea.

__________________________

* Download — pdf format 8 Mo —