The threats are legion. Habitat destruction, rampant overfishing, contamination, global warming, massive runoff of agricultural fertilisers and inpouring sewage are taking their toll on 17,000 species that inhabit this sea. "And these threats will probably grow in future, especially the ones associated with climate change and habitat degradation,” according to one of the study coordinators, Marta Coll, a researcher at theInstitute of Marine Sciences(ICM) in Barcelona.

Havoc in the Mediterranean

And there are more dangers lurking. According to the new study, which is part of an international project to compile a Census of Marine Life, an army of over 600 alien species have invaded the Mediterranean. Over half of them are from the Red Sea, they enter through the Suez Canal. Another 22% of the invaders arrive by boat from other regions of the world. And one in ten invasive species is a fish farm escapee.

It is hard to forecast the havoc these invaders may wreak in the Mediterranean. The authors of the study, which came out today in the magazine PLoS ONE, recall the case of the jellyfish Mnemiopsis leidyi: it reached European waters by boat from the northeast Atlantic and, by 2009, had expanded its domain from Israel to Spain. In the 1980s, this medusa ravaged the Black Sea, causing a collapse in the anchovy populations and severe economic losses.

Most endangered species are corals

Many of these invasive species come from tropical seas and thrive in the warming waters of the Mediterranean. Over the course of the 1980s, the temperature at sea surface along the Mediterranean coast ranged from 16.25°C in the western waters to 22.75 degrees over in the east. At any rate, the scientists predict that by around 2050 the temperature will exceed 24°C in some areas, says Bhavani Narayanaswamy, European spokeswoman for the Marine Life Census.

"Some of the most endangered Mediterranean species are corals from deep, cold waters. There is no way for them to escape the warming water, so their populations are shrinking,” laments Narayanaswamy, who fears “local extinctions” in the offing. "Never before have so many species been studied over such a large geographic area. This work should alert policymakers,” hopes one author of the study, biologist Daniel Oro, from the Mediterranean Institute of Advanced Studies in the Balearic Islands.

75% of deep-sea species still unknown

The Horizon 2020 initiativestarted up by the European Commission four years ago is the closest thing to any large-scale effort to save the Mediterranean. Its aim is ambitious: to drastically beat back the contamination. The figures from the EU executive itself show the daunting magnitude of the challenge. Over 140 million people live on the Mediterranean coasts, and another 175 million regularly visit the region every year. In 2025, half the Mediterranean coast will be urbanised, buried in cement. According to the Commission, 80% of the pressures on marine organisms stem from terra firma. More than half the urban centres with a population of over 100,000 lack sewage treatment plants. And 60% of the plants empty directly into the sea.

Narayanaswamy is sceptical about the project’s prospects: "I’m not sure reducing runoff from industry, agriculture and urban developments will restore the Mediterranean ecosystem to what it was.” To co-author Josep María Gasol from the ICM in Barcelona, "The most surprising thing was to find we don’t know anything.” The new Marine Life Census figures put the number of identified marine species in the Mediterranean Basin at 17,000, almost double the previous estimates. But 75% of the deep-sea species are still unknown – and could disappear without anyone’s sounding the alert.