Spatial variation of vegetative growth of the introduced species Caulerpa scalpelliformis along La Guajira Peninsula, Colombia

Invasive macroalgae represent a major threat to marine biodiversity and may modify the invaded habitat, displace native species, and form monospecific beds altering the tridimensional structure of the ecosystem. Several species of the genus Caulerpa are high-profile invaders, with very aggressive behavior and high expansion rates. We report, for the first time, the presence of Caulerpa scalpelliformis in Colombia, along the Caribbean coast of La Guajira peninsula. The alga was observed both on rocky shores and in seagrass beds at several locations, which indicates that the species is well established. The alga has two different growth forms, at one location, the erect fronds reached 35 cm in length, a size never reported before for the species. At the other sites, the fronds were much smaller. The population with large fronds was observed at a site where raw sewage discharge takes place. The species has shown invasive behavior in Brazil, where it has displaced the dominant native taxon Sargassum vulgare. La Guajira peninsula harbors more than 80% of the seagrass beds of Colombia, and the presence of this introduced species justifies the start of a monitoring program to determine its effect on the ecosystem.