Studies on the Marine Fouling Alga Ulothrix flacca (Dillwyn) Thuret

Marine biofouling is a worldwide problem which costs billions of pounds each year in purchasing and applying the antifouling products in order to clean the fouled surfaces and to repair the damages caused by fouling organisms. Recent immersion panel trials and examination of the fouling literature have revealed the marine green macroalga Ulothrix flacca to be a major pioneering fouling organism on toxic surfaces. Despite its importance, virtually nothing is known about this alga in a fouling context. The present study addressed this issue and attempted to provide a better understanding of its biology, its fouling role and aspects of its resistance to current antifouling biocides and heavy metals. The toxicity of biocides and heavy metals was tested only on the vegetative growth of U.flacca, because spore production could not be carried out. In order to produce vegetative material, investigation of the effects of light quality on the life cycle of U.flacca was carried out. White (control), blue, green, red and yellow lights were used, and only yellow light has been found to be the one to block spore production while producing a vegetative growth in the same quantity as the control. Then, all the bioassays were carried out under yellow light. The biocides investigated were Irgarol 1051©, Preventol A6© and Sea-Nine 211© and the heavy metals were copper, cadmium and zinc. Laboratory studies, using varying concentrations of the toxins, gave EC50 values after 1 and 2 weeks of 204 μg.L-1 for Irgarol,1 μg.L-1 for Preventol, 903 μg.L-1 for Sea-Nine. This order of toxicity, Preventol>Irgarol>Sea-Nine was not found after 3 weeks of treatment where Irgarol showed a better efficacy. Concerning the heavy metals, laboratory studies showed EC50 values after one week of 2213μg.L-1 for copper, 2906μg.L-1 for cadmium, 4903μg.L-1 for zinc. After one week of treatment, Preventol is far more efficient than any other toxin used. The scanning electron microscopy studies looked at the different stages of the life cycle of U.flacca focusing on the attachment mechanisms, which enable its strong adhesion to the surface. The result of these studies showed the high tolerance of U.flacca to common toxins and the results could lead to further research in order to find alternative antifouling products with a lower environmental cost.