Acute dimethyl phthalate exposure impairs tissue integrity in a model cnidarian without disrupting symbiosis

In addition to heat waves and diseases that continue to decimate coral reef ecosystems, corals must increasingly contend with growing concentrations of microplastics in the oceans. Phthalates (PAE), a class of commonly used plasticizers, readily leach from plastics into marine environments and may pose threats to cnidarian health and coral symbiosis. To assess the acute effect of phthalate exposure, we investigated the impact of dimethyl phthalate (DMP) on the model cnidarian Exaiptasia diaphana. Anemones were exposed to four treatments across three weeks to the following: a control, and DMP concentrations of 2.9 mg/L, 15.3 mg/L, and 29.4 mg/L. Changes to photosynthesis, symbiont density, and visual changes to the host anemone tissue integrity were measured. DMP exposure did not significantly affect symbiont density (i.e., bleaching rate) or photosynthetic efficiency (Fv/Fm) of the algal symbionts. However, marked degradation of host tissue was observed in the chemically-treated anemones. These findings raise concerns that PAEs, if their concentrations continue to rise, could contribute to the decline of reef ecosystems by weakening host resilience, even in the absence of symbiosis breakdown.