Madrid - There is no sea like the Mediterranean, which links three continents and has contributed to the development of human civilization for millennia. Today, however, the sea the Romans called Mare Nostrum (Our Sea) evokes ugly images of pollution and concrete apartment blocks rather than that of the goddess Aphrodite rising from its foamy waves. Pollution, oil spills and global warming are affecting the Mediterranean with a frightening speed, environmental organizations warn in Spain, one of the 21 countries bordering the sea which is almost completely enclosed by land. More than 1,500 endemic or nearly endemic marine plant or animal species are under threat, Ricardo Aguilar, an expert on the Mediterranean with the environmental group Oceana, told Deutsche Presse-Agentur dpa. "It would be exaggerated to say that the Mediterranean will die, but it is in a serious danger of suffering a great impoverishment in terms of plant and animal diversity," Aguilar said. The alarm raised by groups such as Oceana can be corroborated by almost any Spanish swimmer who has seen bottles, cans, plastic bags or other types of garbage floating on the waves. Spain has also seen the beauty of its Mediterranean coast disappear beneath strings of hotels and holiday apartments, which are responsible for part of the pollution. About 200,000 ships crisscross the Mediterranean every year, releasing up to 650,000 tons of oil into the water and making the Mediterranean the world's oiliest sea. At the same time, global warming is causing the sea level, water temperature and saltiness to rise, aggravating the threat to coastal ecosystems and to underwater life. About 150 million people live around the Mediterranean, and more than 100 million tourists come to its shores annually. The most polluted parts of the Mediterranean include the coasts of highly industrialized countries - Spain, France, Italy - and river mouths with dams, Aguilar explains. In Spain, for instance, about 800 municipalities systematically disobey rules on waste water, which is poured into the sea without purifying it first, according to local press reports. The Western Mediterranean has 1,900 pieces of garbage - mainly plastic - per square kilometre on its sea bed on the average, more than any other sea, according to figures given by the environmental group Greenpeace. A plastic bottle, for instance, can take centuries to disintegrate. Ships and boats routinely release fuel and other effluent into the sea. The joint impact of such spills is more harmful than that of major environmental disasters, Aguilar says. Contamination from garbage, waste water and oil affects fish and other animals, entering the food chain and leaving local people at risk of eating the pollution they produce. At the same time, the Mediterranean will offer less and less nourishment, with 65 per cent of its fish stocks estimated to be outside safe limits because of overfishing. If the sea level continues rising with the current speed, southern Spanish shores will retrocede by about 10 metres by 2050 on the average, according to a study by the University of Cantabria. Surface water temperature has risen by up to half a degree centigrade over the past 50 years, and the water is also becoming saltier. "The excess of heat in the water is killing typical Mediterranean species such as certain corals, sea fans and sponges," Aguilar says. "Millions of corals have died in the recent years."Seaweed, fish, molluscs and crustaceans also face the threat of invading tropical species, which come in for instance on ship hulls and can now survive in the warmer water. Global warming is also damaging beach ecosystems. The rising sea meanwhile washes sand to the sea bed, where it suffocates plants, Aguilar explains. Less than 1 per cent of the Mediterranean is currently under environmental protection, while scientists recommend protective measures for up to a half of it. In Spain alone, it would cost 5 billion euros (7 billion dollars) to rescue nothing but the coastal landscape with measures such as demolishing illegally erected buildings, the Environment Ministry estimates. "Many agreements have been signed to protect the Mediterranean, but most of them are not applied. Governments still see the Mediterranean mainly as a tourist destination," Aguilar complains. Saving the Mediterranean would not be easy, as it would require joint action from countries differing from each other politically, culturally and, above all, in terms of their wealth, he admits.