Organic solvents alter photophysiological and oxidative stress profiles of the coral Zoanthus sp. – Towards an optimization of ecotoxicological protocols

Highlights: • The effect of organic solvents in photosynthetic corals was unassessed until now; • Zoanthus sp. was exposed to ethanol, methanol and dimethyl sulfoxide; • Oxidative stress, energetic budget and photophysiological profile were measured; • LOEC for ethanol was 0.03 mL L⁻¹, for methanol 0.01 mL L⁻¹ and DMSO 0.01 mL L⁻¹; • Ethanol did not affect zoanthids three times above the general recommendations Coral reefs are declining, affected by climate change and escalating anthropogenic pressures, such as pollution or habitat alteration. Consequently, ecotoxicological assays with tropical corals have increased, specifically towards the study of emergent or persistent pollutants. However, standardized methodology to test for corals is non-existent, and their response to organic solvents, recurrently required in ecotoxicological appraisals, remains unknown. Therefore, we aimed to establish a threshold for the safe use of the selected solvents in ecotoxicological studies with these organisms. We assessed the oxidative stress response (antioxidant response and oxidative damage), cellular energy allocation and photophysiology of the photosynthetic coral Zoanthus sp. (Anthozoa, Hexacorallia) exposed to six doses of three different organic solvents (ethanol, methanol and dimethyl sulfoxide – DMSO). Our results suggest that the coral is more sensitive to methanol and DMSO than to ethanol. Methanol and DMSO LOEC were 0.01 mL L⁻¹ affecting maximum quantum yield (F_v/F_m) and glutathione S-transferase (GST) activity, respectively, while for ethanol was 0.03 mL L⁻¹, influencing F_v/F_m. Despite the higher tolerance of Zoanthus sp. to ethanol, 2.9 mL L⁻¹ of this organic solvent was the only treatment causing mortality. Based on these findings, thresholds for the use of organic solvents with tropical corals can now be adopted. Nevertheless, species specificities should not be overlooked.