Sea Grapes Caulerpa racemosa
This seaweed has creeping stolons (stems) that anchor it to rocks or in sand, and from which arise upright shoots covered with round sacs, or vesicles, hence the common name sea grapes. Each plant is a single huge cell. Old plants may become densely branched and entangled, growing to 6 ft (2 m) across. There are many varieties of sea grapes, and around 60 species of Caulerpa worldwide.
A strain of Caulerpa taxifolia that is widely used in marine aquariums is an invasive species. It is toxic to grazers, grows rapidly, and forms a dense, smothering carpet on the seabed. In 1984 it was discovered in the Mediterranean off Monaco, and has since spread rapidly along the coast, altering native marine communities.