Common types of microdebris affect the physiology of reef-building corals

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 verrucosaandStylophora 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, withP. verrucosabeing more affected thanS. pistillata. Both species showed increased volume growth in response to the microdebris treatments, accompanied by decreased calcification inP. verrucosa. Photosynthetic efficiency of the symbionts was enhanced in both species. The species-specific physiological responses might be attributed to feeding reactions, withP. verrucosaresponding significantly more often to microdebris thanS. 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.HighlightsThe 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