Greening of the Sea Gives Adriatic States the Blues

The pristine waters of the Adriatic have long been the boast of the countries with coastlines alongside it. Azure in colour and much cleaner than the adjoining Mediterranean, they are a major draw for the growing numbers of foreigners holidaying in Slovenia, Croatia, Montenegro and more recently, Albania. With the decline of heavy industry in all, these waters constitute a precious economic asset.

Now they face a new danger. Year by year, an insidious green underwater predator is making its stealthy advance, disturbing the marine environment as it does so and turning pristine sandy and rocky seabeds into thick carpets of waving green fronds.

The state of the once clear waters around the Ligurian island of Elba is a stark warning of what the Adriatic may expect. Formerly home to beds of dazzling coral and molluscs, they were a paradise for divers. “Today, no one goes there for diving,” Professor Francesco Cinelli, a marine biologist at the University of Pisa, laments, peering into the water at the village of Marina di Pisa. “The seabed is covered by a green carpet”, he explains.

Professor Cinelli is talking about Caulerpa Racemosa, an invasive algae that has spread like wildfire in the Mediterranean, and now threatens to do the same in the Adriatic.

The plant is not merely unattractive. Forming dense colonies on all types of seabeds, in both clean and in polluted waters, it transforms the characteristics of its adopted habitat, dramatically reducing the variety and abundance of other underwater fauna. Rapidly growing on all surfaces and in both cold and warm water, it blocks out the sunlight that smaller marine plants need, causing their death. In addition, the algae releases alkaloid substances that kill all other organisms in its vicinity. By destroying rival flora as it covers the seabed, it also impairs the survival of fish and molluscs that feed on other underwater plants, or which require bare sand or rock as a habitat. Sole and spider fish are especially endangered, as they require sandy seabeds.

“When Caulerpa covers the seabed like a carpet, these species lose their natural habitat,” says Ante Žuljević of the Institute for Oceanography and Fishery in Split, Croatia. The spread of the algae into the rest of the Adriatic and the Mediterranean, therefore, will deplete economically viable edible fish stocks as well as deter divers and tourists. Seas renowned for numerous fish species and for the beauty of their underwater landscape could turn into monotonous underwater deserts.

Scientists say if governments in Italy, Slovenia, Croatia, Montenegro and Albania fail to take concerted action to eradicate the scourge, it is likely to spread beyond their control. Yet in spite of the serious nature of the threat, governments in the Adriatic region have so far shown no sign of cooperating among themselves, nor have they actively sought advice from other EU countries, such as France, Italy and Spain, which have already faced this problem and worked together to limit the damage.


Coming to a sea near you

The existence of Caulerpa Racemosa in the Mediterranean was first noted some 80 years ago. A tropical species originating in the Red Sea, it came through the Suez Canal in the early 1930s and gradually took over more than 50,000 hectares of the seabed. Designated by the European Commission as a serious threat to marine biodiversity some ten years ago, it has since advanced across the Mediterranean and into the Adriatic with growing speed.

After its initial appearance off Libya about 20 years ago, it moved to the coastal waters of other Mediterranean countries on sea currents. Man inadvertently carried these marine hitchhikers on the bottoms of ships, their anchors and on fishing nets and diving equipment. Each time an “infected” boat anchored or discharged ballast water at a port of call, algae fell off and found new habitats.

Arriving later to the Adriatic, Caulerpa Racemosa has, in the last three years alone, spread in Montenegrin waters from two to eight locations. The biggest infested area is around the Luštica peninsula at the entrance to the Bay of Kotor, where the algae has spread over two square kilometres. Two new outbreaks were recently spotted there and in the immediate vicinity of the resort of Budva, south of Kotor. By late August, it was estimated that the algae covered a total of over four hectares of the Montenegrin seabed.

In Croatia, the scourge is worse. After first appearing near the Pakleni Otoci, a group of islands in central Dalmatia, a total of 54 locations have become infected. It was also reported recently in the waters off the island of Mljet, a national park whose blue seas are an important attraction for visitors.

The fact that the algae has no natural enemies in the Mediterranean has assisted its spread. So has insufficient awareness of the seriousness of this problem. Long after it appeared, France, Italy and Spain failed to take much notice, and by the time they realised the nature of the threat, it was too late.

Today, the waters off Elba are not the only ones in the Mediterranean suffering massive infestation. Much the same has happened to the seabed off Monaco, on the Cote D’Azur, according to Thierry Thibeau, a researcher from Nice University. There, the algae has driven out rival flora and fauna. “Divers don’t want to dive around Monaco since there is only a green carpet of Caulerpa there now,” Thibeau maintains.