Major ascidian species with negative impacts on bivalve aquaculture: Current knowledge and future research aims

Biofouling constitutes one of the main obstacles in the sector of shellfish farming. Under this perspective, it is of highly importance to critically combine the updated information regarding the invasive potential of ascidian species, together with the factors contributing toward these events. The biological features of each species in relation to the gathering of the main non-indigenous species in the Mediterranean basin represent the first step toward mitigation of negative effects of the phenomenon. Further, there are limited studies investigating the physiological changes of bivalves caused by biofouling while leading to an increase in stress biomarkers. In the present review, the major ascidian species negatively affecting bivalve culture in the Mediterranean Sea are presented, alongside monitoring of ascidians from four Greek mussel farming locations as typical mussel culture cases. Among the main ascidian species, Styela plicata, Clavelina oblonga, Ciona robusta, Aplidium sp., Didemnum sp., Botryllus schlosseri, and Didemnum drachi are included, with the last three being the most harmful for this aquaculture sector. Based on the existing literature and research conducted so far, future research directions are proposed, in an effort to effectively control or efficiently manage ascidian biofouling organisms. Overall, perspectives toward the way we manage the biofouling phenomenon, such as the use of ascidian’s by-products in feedstuffs, chemical and pharmaceutical industry, or their incorporation in bivalve co-culture and integrated multi-trophic aquaculture systems represent promising alternative approaches.