Thomas Belsher

The Introduced Green Alga Caulerpa Taxifolia Continues to Spread in the Mediterranean

The tropical green alga Caulerpa taxifolia in the Mediterranean has spread steadily since its introduction in 1984. At the end of 2000, approximately 131 km2 of benthos had been colonized in 103 independent areas along 191 km of coastline in six countries (Spain, France, Monaco, Italy, Croatia and Tunisia). Large regions neighboring the invaded areas appear favorable to further colonization, and there is thus no reason to believe that spreading will slow down in the years to come.

Sargassum muticum begin to invade the mediterranean

Abstract In the Mediterranean, the Japanese brown alga Sargassum muticum (Yendo) Fensholt is no longer confined to the relatively closed Thau lagoon (France), but is spreading along the Languedoc open-sea coasts: 11 new localities, from Grau du Roi (Gard) to Port-la-Nouvelle (Aude), are mentioned.

Deep-water dispersal of the tropical alga Caulerpa taxifolia introduced into the Mediterranean

Abstract The deep-water dispersal of the tropical alga Caulerpa taxifolia (Vahl) C. Agardh, introduced into the Mediterranean in 1984, was investigated. Observations made from the French Navy submarine “Griffon” showed the presence of the alga at depths of 45–100 m off the most densely invaded coast (near Monaco). The alga was mostly found drifting on the muddy bottom and occasionally fixed on solid substrates.

Standardization proposal for the mapping of Caulerpa taxifolia expansion in the Mediterranean sea

Fourteen years after the first observation of Caulerpa taxifolia (Valh) C. Agardh in the northwestern Mediterranean Sea, this green alga of tropical origin is now present in five countries (Spain, France, Monaco, Italy and Croatia). By the end of 1997, more than 46 km2, at depths of between 0 and 50 m, were found to be affected by this expansion. A standardization of the cartographic procedure is proposed here. Such a standardization is necessary to compare maps produced by various organizations from different countries. For a given independent station, it is based on the definition of three levels of colonization: • - Level I refers to a station where one or several colonies less than 100 m apart cover a total surface area inferior to 1000 m2; • - Level II refers to a station where several colonies less than 250 m apart totally cover more than 1000 m2 with fragments and small colonies dispersed over a surface area inferior to 10 ha; • - Level III is attained when several large colonies are dispersed over a surface area superior to 10 ha, with a total covered surface of more than 1000 m2, impossible to map with precision due to its size. For each of these colonization levels, descriptive parameters can be used to precisely describe the situation: covered surface area, dispersion surface (i.e. “affected” zone), estimation of very large affected zones (i.e. “concerned” zones) and the portions of the coastline along which an affected or concerned zone can be found.