The impact of the ascidian Styela clava Herdman on shellfish farming in the Bassin de Thau, France

The solitary ascidian Styela clava Herdman, 1882 has recently been found in the Bassin de Thau, on the French Mediterranean coast, an area of intensive oyster and mussel farming. S. clava has the potential to greatly reduce oyster production in the Bassin de Thau by competing with the oysters for food. An understanding of how this species arrived in the Bassin de Thau and why the population growth is limited at present may provide clues to suitable management options to prevent its further spread. The potential impact of S. clava on the wider Mediterranean shellfish industry is considered.