E-commerce and Caulerpa: unregulated dispersal of invasive species

Professional aquarists and hobbyists are thought to be the source of invasions of the aquarium strain of the green macroalga Caulerpa taxi folia in the Mediterranean, southern California, and Australia. The US Department of Agriculture, Animal and Plant Health Inspection Service (USDA-APHIS) restricted interstate commerce and importation of the Mediterranean clone of C taxi folia prior to the California invasion and is currently deciding if it should strengthen regulation of this genus as more species of Caulerpa are being described as invasive. Here we document the importance of e-commerce as a mode of dispersal for many species of Caulerpa in the United States. We purchased Caulerpa from 30 internet retailers and 60 internet auction sites representing 25 states and Great Britain. Twelve different Caulerpa species were confirmed using DNA sequencing. Only 10.6% of sellers provided the correct genus and species names with their shipments. Thirty purchases of "live rock" provided four species of Caulerpa, as well as 53 additional marine species. Our results confirm the extensive e-commerce availability of this invasive genus and its high dispersal potential via postal services and hobbyists. We recommend that both eBay and the USDA maximize regulation of Caulerpa.