Impact of antifouling booster biocides on single microalgal species and on a natural marine phytoplankton community

Phytoplankton were exposed to 4 antifouling booster biocides (Sea-Nine 211®, Irgarol 1051®, diuron and zinc pyrithione) to investigate toxicological responses. Initially, single species/single biocide exposure experiments revealed changes in pigment ratios under all biocide exposures for the prymnesiophyteEmiliania huxleyi, but not for the cyanophyteSynechococcussp. Growth inhibition results following 72 h exposures indicated thatSynechococcussp. was more tolerant to zinc pyrithione (NOEC of 1.0 μg l–1) and Sea-Nine 211®(NOEC of 0.9 μg l–1) thanE. huxleyi(EC50of 0.54 and EC50of 0.35 μg l–1, respectively). In contrast,Synechococcussp. was more sensitive to diuron (EC50of 0.55 μg l–1) thanE. huxleyi(EC50of 2.26 μg l–1), whereas exposure to Irgarol 1051®similarly impacted both species (EC50of 0.16 and 0.25 μg l–1, respectively). In addition, the impact on photosynthesis and on pigment chemotaxonomy was investigated through a laboratory exposure experiment using a natural phytoplankton community. Pigment signatures were measured by High Performance Liquid Chromatography (HPLC) and densities of size-classified phytoplankton groups were monitored using Analytical Flow Cytometry (AFC). Group-specific sensitivity of the natural phytoplankton community was detected through pigment composition after 72 h exposure to 5 μg l–1zinc pyrithione and 10 μg l–1Sea-Nine 211®. Zeaxanthin increased proportionally, indicating a relative increase in Cyanophyceae. This result was corroborated using AFC. Primary production, estimated by14C-HCO₃⁻ uptake, was compared to maximum quantum yield of Photosystem II (F V/F M), which was quantified by Fast Repetition Rate Fluorimetry (FRRF). The 2 techniques were in good agreement (R² = 0.89, p = 0.0001), both primary production andF V/F Mbeing impaired by exposure to all biocides tested. These results are discussed in the context of the potential environmental impact of biocides on phytoplankton communities and the ecological implications of any modifications in species composition.