The chronic exposure to pharmaceuticals and phtalates results in sub-lethal effects in the zooxanthellate coral Balanophyllia europaea

Corals are fundamental elements of rocky shore ecosystems, which are threathened by wastewater and river discharges, tourism and climate change. Among many threats, that posed by emerging contaminants still needs to be throughly investigated. The aim of this study was to test wether a prolonged exposure to low concentrations of pharmaceuticals and bisphenol A (BPA) might affect the common and widespread shallow water zooxanthellate coral Balanophyllia europaea. B. europaea polyps were collected at 6 m depth in Calafuria (LI, Italy) in May 2023 and 2024, soon before the brooding period. B. europaea larvae were exposed to Carbamazepine (CB), Ibuprofen (IB) and Valsartan (VS) at 1-10 µg/L and to BPA at 10-100 µg/L, both separately and as mixtures (MIX_L: 1 µg/L CB, IB, VS + 10 µg/L BPA; MIX_H: 10 µg/L CB, IB, VS + 100 µg/L BPA), for 4 weeks. Toxicity endpoints were: mortality, metamorphosis and the average amount of chlorophyll (Chl) a-c2/larva. Adults of B. europaea were exposed to MIX_L and MIX_H for 4 weeks, and toxicity endpoints were: Chla-c2/zooxanthellae, Chla-c2/coral surface, zooxanthellae/coral surface and the predation ability. Results showed no significant mortality for the larvae but an alteration in their ability to metamorphosize, which was reduced for larvae exposed to single pharmaceuticals but was enhanced for those exposed to BPA. In the adults, the ratio Chla-c2/zooxanthellae was significantly reduced upon exposure to both MIX_L and MIX_H, as well as the ratio Chla-c2/coral surface, while the ratio zooxanthellae/coral surface showed a slight increase. The predation ability resulted reduced in specimens exposed to both mixtures. The overall results showed that the prolonged exposure to low concentrations of pharmaceuticals and BPA might impact both larvae and adults of B. europaea and that the chlorophyll content, the metamorphosis and the predation ability might represent sensitive endpoints for the impact of such compounds.