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The comparative effects of chronic microplastic and sediment deposition on the scleractinian coral Merulina ampliata
Summary
Researchers exposed tropical coral fragments to PET microplastics and natural sediment particles over 28 days and found no meaningful difference in coral growth, symbiotic algae density, or chlorophyll levels between the two. While microplastic particles were physically incorporated into coral skeletons, the coral species studied appeared resilient at the tested concentrations, suggesting microplastics may not pose a greater threat to this species than ordinary sedimentation stress.
Despite increasing research into the effects of microplastics on corals, no study to date has compared this relatively novel pollutant with a well-established stressor such as downwelling sediments. Here, Merulina ampliata coral fragments were exposed to polyethylene terephthalate (PET) and calcium carbonate particles (200-300 μm) at two deposition levels, high (115.20 ± 5.83 mg cm d, mean ± SE) and low (22.87 ± 1.90 mg cm d) in specially-designed Flow-Through Resuspension (FloTR) chambers. After 28 d, there were no significant differences between fragments exposed to sediments and microplastics for coral skeletal growth, Symbiodiniaceae density, and areal or cellular chlorophyll a concentrations. There were also no significant differences between levels of treatments, or with the control fragments. More PET microplastic particles were incorporated into the coral skeletons of fragments exposed to microplastics compared to those exposed to sediment and the control fragments, but there was no difference between fragments exposed to high and low microplastic levels. Together, the results show that M. ampliata appears to be able to cope with both microplastic and sediment stress, and suggests that microplastics do not represent a more serious threat than downwelling sediments at the levels tested.
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