Formation of propagules on an invasive strain of Caulerpa racemosa (Chlorophyta) in the Mediterranean Sea

An invasive strain of Caulerpa racemosa has been spreading rapidly in the Mediterranean Sea since 1990. It reproduces itself sexually or by random fragmentation of the thallus. We report a new way of vegetative reproduction: a specific fragmentation process involving detachment of ramuli. The ramuli of the invasive strain of C. racemosa are cylindrical to clavate, with a rounded apex and a slight constriction at their insertion on the rachis of the frond. They detach themselves from the fronds and form fine coenocytic chlorophyllous filaments. The production of these propagules may explain the regeneration of C. racemosa meadows, which disappear in certain regions during winter, and may also account for the rapid dissemination of the alga.