Tirpitz, V. | bioRxiv Science

bioRxiv2023

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

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. HighlightsO_LIThe effects of major sources of microdebris pollution on coral physiology were compared. C_LIO_LIOverall, microdebris had only minor impacts on coral physiology. C_LIO_LIArtificial fibers and tire wear caused the strongest effect on coral physiology. C_LIO_LISingle polymer and complex microdebris caused similar, yet species-specific effects. C_LIO_LISpecies-specific effects might be due to different feeding behaviors. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/569976v1_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@1ba7ba8org.highwire.dtl.DTLVardef@c5795org.highwire.dtl.DTLVardef@4a10deorg.highwire.dtl.DTLVardef@9983e5_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2021

Interactive effects of microplastic pollution and heat stress on reef-building corals

Plastic pollution is an emerging stressor that increases pressure on ecosystems such as coral reefs that are already challenged by climate change. However, the effect of plastic pollution in combination with global warming is largely unknown. Thus, the goal of this study was to determine the cumulative effect of microplastic pollution with that of global warming on reef-building coral species and to compare the severity of both stressors. For this, we conducted a series of three controlled laboratory experiments and exposed a broad range of coral species (Acropora muricata, Montipora digitata, Porites lutea, Pocillopora verrucosa, and Stylophora pistillata) to microplastic particles in a range of concentrations (2.5-2,500 particles L-1) and mixtures (from different industrial sectors) at ambient temperatures and in combination with heat stress. We show that microplastic can occasionally have a negative effect on the corals thermal tolerance. In comparison to heat stress, however, microplastic constitutes a minor stressor. While heat stress led to decreased photosynthetic efficiency of algal symbionts, and increased bleaching, tissue necrosis, and mortality, treatment with microplastic particles had only minor effects on the physiology and health of the tested coral species at ambient temperatures. These findings underline that while efforts to reduce plastic pollution should continue, they should not replace more urgent efforts to halt global warming, which are immediately needed to preserve remaining coral reef ecosystems. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=108 SRC="FIGDIR/small/454458v1_ufig1.gif" ALT="Figure 1"> View larger version (51K): org.highwire.dtl.DTLVardef@c2eeb0org.highwire.dtl.DTLVardef@1c49ea6org.highwire.dtl.DTLVardef@18bab59org.highwire.dtl.DTLVardef@9e952b_HPS_FORMAT_FIGEXP M_FIG C_FIG

ecology↗