Differential enrichment and physiological impacts of ingested microplastics in scleractinian corals in situ

Microplastics are emerging contaminants and widespread in the ocean, but their impacts on coral reef ecosystems are poorly understood, and in situ study is still lacking. In the present study, the distribution patterns of microplastics in the environment and inhabiting organisms were investigated along the east coast of Hainan Island, South China Sea, and the physiological impacts of the microplastics on scleractinian corals were analyzed. We documented average microplastic concentrations of 14.90 particlesL^-1 in seawater, 343.04 particleskg^-1 in sediment, 4.97 particlescm^-2 in corals, and 0.67-3.12 particlescm^-1 in Tridacnidae, Trochidae and fish intestines. Further analysis revealed that the characteristics of microplastics in the organisms were different from those in the environment, indicating preferential enrichment in the organisms. Furthermore, there was an obvious correlation between microplastic concentration and symbiotic density in corals. Furthermore, caspase3 activity was significantly positively correlated with the microplastic content in the small-polyp coral Pocillopora damicornis, but the large-polyp coral Galaxea fascicularis showed higher tolerance to microplastics. Taken together, our results suggest that microplastics are selectively enriched in corals and other reef-dwellers, in which they exact differential stress (apoptotic) effects, with the potential to impact the coral-Symbiodiniaceae symbiosis and alter the coral community structure.