Algae in the Adriatic: A Rapidly Growing Problem

27/01/2005

The proliferation of two aggressive species of tropical algae along Croatia's Adriatic coastline and nearby islands has alarmed scientists. Over the long term, the problem could threaten tourism.

By Miranda Novak for Southeast European Times in Zagreb – 27/01/05

Croatia, which relies on tourism along its Adriatic coast, fears the spread of algae could affect its appeal. [AFP]

The appearance and rapid spread of tropical algae in the Croatian Adriatic is becoming an increasingly serious problem, according to recent research. Two strains of algae -- Caulerpa Taxifolia and Caulerpa Racemosa -- were discovered in the Croatian part of the Adriatic in 1995. France, Spain and Italy have been struggling with the algae for the last two decades, but with limited success.

Racemosa has been found on many spots around Croatia's southern Adriatic islands, while Taxifolia has so far been found in three places -- Stari Grad and two northern Adriatic islands -- Rab and Krk.

While Racemosa is thought to have come from the Red Sea through the Suez Canal, Taxifolia may have been accidentally introduced into the sea from the oceanographic museum in Monaco 20 years ago.

Racemosa is an exceptionally aggressive species that creates dense settlements. Covering the seabed with several layers, it prevents sunlight from reaching other sea organisms, making photosynthesis impossible. Without food and oxygen, the other sea life dies.

Since the first discovery of the algae, it has spread to as many as 35 locations. The rapid proliferation has surprised scientists, who now warn that some of the affected areas could merge during the next three years.

To date, the worst affected area is the island of Mljet, near the Sobra inlet, where the algae has spread along 11.5km of coastline. The problem is also severe on the nearby island of Bisevo. Biologist Vladimir Onofri says his colleagues were stunned when he showed them a cliff there which is completely covered with racemosa, at depths of 7m to 40m.

Most harmful algae can be held in check by covering them with foil, but not racemosa -- its growth is too rapid. It has no natural enemies in the Adriatic, and its fragments are light and do not sink to the bottom, so the currents spread them.

"The latest testing of the conditions in Mljet, where we tried to destroy the racemosa settlements by covering them with black foil, indicates that within ten days this algae grew underneath the foil a full 27cm. Hence, its daily growth amounted to 2.7cm," Onofri said.

Due to costs, labour conditions and the huge scope of the problem, Croatian scientists have advised the government to concentrate on removing the algae in areas of exceptional cultural and biological importance -- principally Mljet National Park. However, unless the overall problem is addressed, the long-term consequences could be grave. At the rate it is growing, algae could over-run the area in about ten years, making the region less attractive and damaging Croatia's tourist industry -- a major source of the country's economic growth.