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Common types of microdebris affect the physiology of reef-building corals
Summary
Researchers exposed two coral species to four types of microdebris — plastic fragments, synthetic clothing fibers, tire/brake wear particles, and pure microplastic beads — for eight weeks in a lab. Clothing fibers and tire wear particles caused the strongest harm, reducing calcification in one coral species and disrupting normal physiology in both. The study shows that real-world microdebris pollution, which is always a mixture of materials, can stress reef-building corals in ways that studies using single plastic types may underestimate.
Abstract Marine debris, particularly microdebris (< 1 mm) poses a potential threat to marine life, including reef-building corals. While previous research has mainly focused on the impact of single polymer microplastics, the effects of natural microdebris, composed of a mixture of materials, have not been explored. Therefore, this study aimed to assess the effects of different microdebris, originating from major sources of pollution, on reef-building corals. For this, we exposed two scleractinian coral species, Pocillopora verrucosa and Stylophora pistillata , known to frequently ingest microplastics, to four types of microdebris in an 8-week laboratory experiment: fragmented environmental plastic debris, artificial fibers from clothing, residues from the automobile sector consisting of tire wear, brake abrasion, and varnish flakes, a single polymer microplastic treatment consisting of polyethylene particles, and a microdebris-free control treatment. Specifically, we (I) compared the effects of the different microdebris on coral growth, necrosis, and photosynthesis, (II) investigated the difference between the microdebris mixtures and the exposure to the single polymer treatment, and (III) identified potential mechanisms causing species-specific effects by contrasting the feeding responses of the two coral species on microdebris and natural food. We show that the fibers and tire wear had the strongest effects on coral physiology, with P. verrucosa being more affected than S. pistillata . Both species showed increased volume growth in response to the microdebris treatments, accompanied by decreased calcification in P. verrucosa . Photosynthetic efficiency of the symbionts was enhanced in both species. The species-specific physiological responses might be attributed to feeding reactions, with P. verrucosa responding significantly more often to microdebris than S. pistillata . These findings highlight the effect of different microdebris on coral physiology and the need for future studies to use particle mixtures to better mimic naturally occurring microdebris and assess its effect on corals in more detail. Highlights The effects of major sources of microdebris pollution on coral physiology were compared. Overall, microdebris had only minor impacts on coral physiology. Artificial fibers and tire wear caused the strongest effect on coral physiology. Single polymer and complex microdebris caused similar, yet species-specific effects. Species-specific effects might be due to different feeding behaviors. Graphical abstract