Do microplastics affect the zoanthid Zoanthus sociatus?

Microplastics (1 μm–5 mm), a ubiquitous and persistent marine pollutant, pose a severe threat to coral reefs when recently associated with physiological distress and increased diseases on corals. Studies conducted so far have only reported effects on scleractinian species. Knowledge about its effects on other corals (e.g. Order Zoantharia) remains uncovered, and responses at biochemical levels remain poorly documented. This study aimed to assess the potential effects induced by the presence of microplastics (1 and 10 mg L−1 low-density polyethylene, LDPE MP, or polyvinyl chloride, PVC MP) in the tropical and subtropical cosmopolitan species Zoanthus sociatus (order Zoantharia. Anthozoa: Hexacorallia), at organism level (survival and behaviour), endosymbionts (photosynthetic efficiency) and the cellular level (oxidative stress, detoxification capacity and energy metabolism). In a short-term exposure (96 h), this species was more sensitive to PVC MP. The presence of this polymer at a concentration of 10 mg L−1 caused a ten-fold higher adhesion to the coral epidermis, increased photosynthetic efficiency, lipid peroxidation, and antioxidant defences; without, however, inducing energetic costs. Although the observed physiological and biochemical effects did not compromise Z. sociatus survival in the short term, it does not rule out potential long-term (cumulative) effects that could endanger this and other physiologically similar species that underlie coral reefs. [Display omitted] •Microplastics (MPs) may threaten coral reefs due to physiological distress.•Zoanthus sociatus polyps exposed to 1 and 10 mg L−1 LDPE and PVC particles 63–125 μm.•PVC MPs were more harmful to Zoanthus sociatus than LDPE MPs.•PVC MPs altered photobiology and induced oxidative stress on polyps only at 10 mg L−1.•MPs at concentrations below 1 mg L−1 might do not pose a risk to Z. sociatus.