Biological invasions are recognized as a serious threat to marine biodiversity. Within the last two years, invasive populations of Caulerpa taxifolia were found in southern California’s coastal waters as well as in New South Wales, Australia. In addition, two other seaweeds (Undaria pinnatifida and Caulacanthus ustulatus) also appear to have recently invaded southern California’s warm temperate waters. The introduction of C. taxifolia has attracted much attention because this exotic seaweed is thought to have significantly altered the structure of Mediterranean marine ecosystems following its 1984 invasion. The southern California inoculation of C. taxifolia is believed to have resulted from the release of aquarium specimens. Besides C. taxifolia, other species of Caulerpa being sold for aquarium use also may have the potential to invade temperate waters. As a first step towards making this determination, the availability (% frequency) of Caulerpa species being sold in southern California for aquarium use was ascertained. Fifty retail saltwater aquarium stores were visited in three southern California counties between November 2000 and August 2001. Sixteen Caulerpa taxa were identified from the retail aquarium outlets. Caulerpa species were sold in 52% of these stores. Caulerpa taxifolia, “Mediterranean form”, was offered for sale in 10% of the visited stores; C. serrulata var. hummii (18%), C. racemosa (14%), and C. racemosa var. lamourouxii (14%) were the most commonly sold species. These data indicate that the aquarium industry is bringing into the region other species of Caulerpa besides C. taxifolia. Some of these species may also have the potential to invade temperate waters.

Key words: Aquarium Industry, Caulerpa, Invasive species, Macroalgae