Styela clava (Tunicata, Ascidiacea) – a new threat to the Mediterranean shellfish industry?

The solitary ascidian Styela clava Herdman, 1882 has recently been found in the Bassin de Thau, France, an area of intensive oyster and mussel farming. The shellfish are grown on ropes suspended in the water column, similar to the technique employed in Prince Edward Island (PEI), Canada. S. clava is considered a major threat to the mussel industry in PEI but, at present, it is not considered a threat to oyster production in the Bassin de Thau. Anoxia or the combined effect of high water temperature and high salinity may be constraining the growth of the S. clava population in the Bassin de Thau. Identification of the factors restricting the population growth may provide clues to potential control methods.