Case Study: Caulerpa Taxifolia

A decorative aquarium plant, Caulerpa taxifolia, escaped into the Mediterranean in 1984 and is now decorating much of the sea floor along the French, Monaco, and Italian Rivieras from Nice to Imperia. Calerpa taxifolia is a green alga, native to the Caribbean and the Indian and Pacific Oceans, that is present, but normally uncommon, in warm waters. The strain now spreading throughout the Mediterranean was cultivated during the 1970s in the Stuttgart Zoo aquarium and is believed to have been accidentally discharged into the sea by the Oceanographic Museum of Monaco. By 1992, it had spread to cover 1,000 acres of seabed; it now covers more than 10,000 acres.

Caulerpa taxifolia competes with, and often outcompetes, native Mediterranean species. It produces high levels of toxic metabolites, which make it distasteful to herbivores and allow it to supplant native communities. Caulerpa taxifolia monopolizes the water’s oxygen, smothering marine plants such as sea grass and kelp, and its toxins can destroy the eggs of many animal species. It destroys clam beds and fisheries, overcomes corals and sponges, and prevents animals from grazing on invertebrates in bottom muds. Long lived native algae are particularly threatened by this strain, but available data show that invertebrate and fish abundance and diversity are also affected.

Caulerpa taxifolia has now spread to the United States. Discovered June 12, the alga has established a half-acre patch of sea bottom in the Agua Hedionda Lagoon, off Carlsbad, California. Control of Caulerpa taxifolia is difficult. It cannot be dug up because the algae spread through fragmentation and each small piece of the plant can regenerate an entirely new plant. Plant stems can grow to over nine feet long and can survive for up to ten days out of water. Given the regenerative capability of Caulerpa taxifolia, fishing equipment or boat anchors could potentially spread the invasive throughout the coastal waters of the United States. Chemical control is most effective, but requires saturation with chlorine or copper sulfate, which kills everything in the water.

-- Boudouresque, C.-F. "The Great Escape" IUCN World Conservation, April 1997 p. 17-18

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