A comparison of toxicant-induced succession for five antifouling compounds on marine periphyton in SWIFT microcosms

Five antifouling biocides, chlorothalonile, dichlofluanide, medetomidine, tolylfluanide, and zinc pyrithione, were evaluated regarding their effect on the composition of the periphyton community and the subsequent toxicant-induced succession (TIS). The periphyton communities were exposed in a semi-static setting for 96 h using a SWIFT microcosm. As a measure of community composition, pigment profiles from the exposed communities were used as effect indicators and compared with unexposed parts of the same community using the Bray–Curtis dissimilarity index. Chlorothalonile caused changes in the community starting at 85 μg l^?1 while dichlofluanide had no effect even at the highest concentrations used, 810 μg l^?1. The related substance tolylfluanide only affected the community composition at 2700 μg l^?1. Medetomidine had a different response curve with a small effect on the community composition at 0.8 μg l^?1 which then disappeared only to reappear at 240 μg l^?1. Zinc pyrithione had the largest effect on the periphyton community with changes starting at 10 μg l^?1 and no detectable pigments at 100 μg l^?1. The changes in the community composition for the five substances were also compared using multidimensional scaling. When all substances were analyzed and plotted together, chlorothalonile, dichlofluanide, medetomidine, and tolylfluanide showed surprisingly similar effects compared to zinc pyrithione that gave very different TIS. However, when only chlorothalonile, dichlofluanide, and tolylfluanide were plotted together, clear differences in TIS between the three toxicants were revealed. Dichlofluanide only induced small effects, while concentration-dependent TIS trajectories for chlorothalonile and tolylfluanide took off in opposite directions indicating very different responses of the periphyton communities. This study demonstrates that substances with a similar chemical structure and mechanisms of action can have different effects on the community composition. With the exception of zinc pyrithione, none of the recorded effect levels were at concentrations reported from marine environments so far.