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Mean ( ± SEM) microplastics ([MP], A,B) and Artemia nauplii (C,D) ingestion rates of corals exposed to ambient (dark bars) and increased (light bars) temperature. Note the difference in scale of the y-axes.

Mean ( ± SEM) microplastics ([MP], A,B) and Artemia nauplii (C,D) ingestion rates of corals exposed to ambient (dark bars) and increased (light bars) temperature. Note the difference in scale of the y-axes.

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Rising sea temperatures and increasing pollution threaten the fate of coral reefs and millions of people who depend on them. Some reef-building corals respond to thermal stress and subsequent bleaching with increases in heterotrophy, which may increase the risk of ingesting microplastics. Whether this heterotrophic plasticity affects microplastics...

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... After offering both types of particles independently, we found that the corals ingested the natural food at a higher rate than microplastics. In general, these findings are consistent with previous studies (Axworthy and Padilla-Gamiño, 2019;Savinelli et al., 2020), although there is also a counterexample (Rotjan et al., 2019). Yet, particle numbers deviated (SD) in average by 38 microplastic particles and 141 Artemia sp. ...
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Microplastics are omnipresent in the oceans and threaten marine animals through physical contact or ingestion. Short-term studies have already shown that reef-building stony corals respond differently to microplastics than natural food. However, it remains unknown whether corals exhibit acclimation mechanisms to combat the effects of microplastic exposure. Specifically, the long-term effects of microplastics on the feeding and defense behavior of reef-building corals remain unexplored. Therefore, the goal of this study was to infer potential acclimation mechanisms in the behavior of the corals. For this, four reef-building species (Acropora muricata, Porites lutea, Pocillopora verrucosa, and Heliopora coerulea) were exposed in a long-term experiment to microplastics for 15 months. Subsequently, coral feeding rates on microplastics and natural food (Artemia sp. cysts), feeding discrimination, and reactions to both were assessed in a 24 h pulse exposure experiment. The results showed that corals’ feeding rates did not decrease after long-term exposure to microplastics. Similarly, the feeding discrimination (i.e., ratio of feeding on microplastics and natural food) did not differ after long-term exposure to microplastics. Moreover, corals showed no changes in defense behavior (i.e., mucus production or extrusion of mesenterial filaments) against microplastics. These findings suggest that symbiotic, reef-building corals do not develop mechanisms to adapt to long-term microplastic exposure. Thus, microplastic pollution might constitute a constant stressor for coral organisms, likely leading to sustained energy expenditures and impaired health.
... These studies demonstrate that the capture of microplastic particles by anthozoans is not uniform, and responses to microplastics will be different across species. Moreover, mixed microplastic and food treatments have resulted in increased microplastic uptake by some anthozoan species (Axworthy and Padilla-Gamiño, 2019;Romanó de Orte et al., 2019;Savinelli et al., 2020), due to the presence of prey promoting feeding activity (Kamio and Derby, 2017). For example, the coral Pocillopora damicornis and anemone E. pallida ingested significantly more microplastics in the presence of shrimp, while little or no uptake occurred when exposed to only microplastics (Axworthy and Padilla-Gamiño, 2019;Romanó de Orte et al., 2019). ...
... Moreover, mixed microplastic and food treatments have resulted in increased microplastic uptake by some anthozoan species (Axworthy and Padilla-Gamiño, 2019;Romanó de Orte et al., 2019;Savinelli et al., 2020), due to the presence of prey promoting feeding activity (Kamio and Derby, 2017). For example, the coral Pocillopora damicornis and anemone E. pallida ingested significantly more microplastics in the presence of shrimp, while little or no uptake occurred when exposed to only microplastics (Axworthy and Padilla-Gamiño, 2019;Romanó de Orte et al., 2019). ...
... This study observed no significant influence of elevated temperature on fibre or fragment uptake in A. viridis. A similar multi-stressor study using the tropical corals Montipora capitata and Pocillopora damicornis, also found no significant difference in microplastic uptake at ambient (27°C) and increased (30°C) temperatures (Axworthy and Padilla-Gamiño, 2019). Conversely, the anemone E. pallida was more susceptible to microplastic ingestion when thermally stressed (Romanó de Orte et al., 2019). ...
Article
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Microplastics (<1 mm) are ubiquitous in our oceans and widely acknowledged as concerning contaminants due to the multi-faceted threats they exert on marine organisms and ecosystems. Anthozoans, including sea anemones and corals, are particularly at risk of microplastic uptake due to their proximity to the coastline, non-selective feeding mechanisms and sedentary nature. Here, the common snakelocks anemone (Anemonia viridis) was used to generate understanding of microplastic uptake in the relatively understudied Anthozoa class. A series of microplastic exposure and multi-stressor experiments were performed to examine particle shape and size selectivity, and to test for the influence of food availability and temperature on microplastic uptake. All A. viridis individuals were found to readily take up microplastics (mean 142.1 ± 83.4 particles per gram of tissue) but exhibited limited preference between different particle shapes and sizes (n = 40). Closer examination identified that uptake involved both ingestion and external tissue adhesion, where microplastics were trapped in secreted mucus. Microplastic uptake in A. viridis was not influenced by the presence of food or elevated water temperature (n = 40). Furthermore, environmental sampling was performed to investigate microplastic uptake in A. viridis (n = 8) on the coast of southwest England, with a mean of 15.8 ± 4.0 particles taken up per individual. Fibres represented the majority of particles (91%) followed by fragments (9%), with 87% either clear, blue or black in colour. FTIR analysis identified 70% of the particles as anthropogenic cellulosic or plastic polymers. Thus, this study provides evidence of microplastic uptake by A. viridis in both laboratory exposures experiments and in the marine environment. These findings support recent literature suggesting that external adhesion may be the primary mechanism in which anthozoans capture microplastics from the water column and highlights the potential role anemones can play as environmental microplastic bioindicators.
... There is some evidence that other anthropogenic stressors have a synergistic effect with MNPs in Anthozoa. For example, thermally bleached anemones and corals ingested more MNPs relative to prey, and experience greater internal exposure to MNPs due to longer retention times [120,121]. This is of particular concern given that coral reef ecosystems are facing increases in frequency and intensity of bleaching events due to ocean warming in conjunction with the predicted increase in MNP exposure. ...
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Plastic pollution in a growing problem globally. In addition to the continuous flow of plastic particles to the environment from direct sources, and through the natural wear and tear of items, the plastics that are already there have the potential to breakdown further and therefore provide an immense source of plastic particles. With the continued rise in levels of plastic production, and consequently increasing levels entering our marine environments it is imperative that we understand its impacts. There is evidence microplastic and nanoplastic (MNP) pose a serious threat to all the world's marine ecosystems and biota, across all taxa and trophic levels, having individual- to ecosystem-level impacts, although these impacts are not fully understood. Microplastics (MPs; 0.1–5 mm) have been consistently found associated with the biota, water and sediments of all coral reefs studied, but due to limitations in the current techniques, a knowledge gap exists for the level of nanoplastic (NP; <1 µm). This is of particular concern as it is this size fraction that is thought to pose the greatest risk due to their ability to translocate into different organs and across cell membranes. Furthermore, few studies have examined the interactions of MNP exposure and other anthropogenic stressors such as ocean acidification and rising temperature. To support the decision-making required to protect these ecosystems, an advancement in standardised methods for the assessment of both MP and NPs is essential. This knowledge, and that of predicted levels can then be used to determine potential impacts more accurately.
... On the other hand, active prey capture and passive suspension feeding account for a small percentage of daily metabolic requirements in healthy corals (Houlbrèque and Ferrier-Pagès, 2009). The heterotrophic feeding behavior leads to MPs consumption by corals from ambient environments (Axworthy and Padilla-Gamiño, 2019;Tang et al., 2021). Recent studies have revealed key patterns of MPs consumption by corals including ingestion, egestion, and retention (Hankins et al., 2018;Rotjan et al., 2019). ...
... MPs as a microbial vector can increase prevalence of coral disease and even mortality (Rotjan et al., 2019). Recently, MPs in combination with thermal stress were also investigated (Axworthy and Padilla-Gamiño, 2019;Mendrik et al., 2021). Since MPs could increase the bioaccessibility of sorbed contaminants and polymer additives, corals may suffer higher bioaccumulation of chemicals during MPs ingestion (Khalid et al., 2021). ...
Article
Marine microplastics (MPs)-induced threats to shallow-water scleractinian corals are a growing global concern that needs interdisciplinary studies. However, it remains uncertain to what extent the ecotoxicological effects of MPs can explain the potential health impacts on corals at the species-specific scale. Using recent datasets of multiple MPs-induced impacts on coral species, we developed an integrated ecotoxicological modeling approach to quantify the MPs–corals interaction dynamics. Toxicokinetic (TK)-based corals ingestion, egestion, and adhesion processes posed by MPs were comprehensively evaluated. Based on estimated uptake and egestion rates, we showed that corals were much likely to bioaccumulate marine MPs. We applied toxicodynamic (TD) models to appraise time- and concentration-dependent response patterns across MPs–corals systems. We found that marine MPs are highly toxic to corals with a median benchmark concentration causing 10% compromised coral health of 20–40 mg L⁻¹ and a mean growth inhibition rate of ~2% d⁻¹. By providing these key quantitative metrics that may inform scientists to refine existing management strategies to better understand the long-term impact of MPs on coral reef ecosystems. Our TK/TD modeling scheme can help integrating current toxicological findings to encompass a more mechanistic-, ecological-, and process-based understanding of diverse coral ecosystems that are sensitive to MPs stressor varied considerably by species and taxonomic group.
... Of the 20 coral-microplastic experiments published to date, less than half exposed corals to microplastics in combination with other common seawater particulates (e.g. microinvertebrates and sediments) 29,36,41,44 . Only one study so far compared how corals react to both sediments and microplastics, briefly documenting that significantly more cnidocytes are fired towards microplastics 29 and no study has addressed whether microplastics compromise sediment rejection efficiency in corals. ...
Article
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Investigations of encounters between corals and microplastics have, to date, used particle concentrations that are several orders of magnitude above environmentally relevant levels. Here we investigate whether concentrations closer to values reported in tropical coral reefs affect sediment shedding and heterotrophy in reef-building corals. We show that single-pulse microplastic deposition elicits significantly more coral polyp retraction than comparable amounts of calcareous sediments. When deposited separately from sediments, microplastics remain longer on corals than sediments, through stronger adhesion and longer periods of examination by the coral polyps. Contamination of sediments with microplastics does not retard corals’ sediment clearing rates. Rather, sediments speed-up microplastic shedding, possibly affecting its electrostatic behaviour. Heterotrophy rates are three times higher than microplastic ingestion rates when corals encounter microzooplankton ( Artemia salina cysts) and microplastics separately. Exposed to cysts-microplastic combinations, corals feed preferentially on cysts regardless of microplastic concentration. Chronic-exposure experiments should test whether our conclusions hold true under environmental conditions typical of inshore marginal coral reefs.
... With respect to their exogenous feeding, coral are suspension feeders, ingesting plankton, both actively and passively, that are entrapped on their tentacles (Fig. 1). In addition to plankton, corals can also ingest microplastics (Hall et al., 2015;Hankins et al., 2018;Rotjan et al., 2019;Corona et al., 2020;Hankins et al., 2021), with smaller pieces likely being inadvertently consumed (Hankins et al., 2018;Axworthy and Padilla-Gamiño, 2019). Ingested plastics may block the gastrovascular cavity of the coral polyp leaving the polyp feeling satiated or may prevent feeding on nutritious food sources, as has been seen in other taxa (McCauley and Bjornal, 1999;Xu et al., 2017;Egbeocha et al., 2018;Ory et al., 2018;de Barros et al., 2020). ...
... Ingested plastics may block the gastrovascular cavity of the coral polyp leaving the polyp feeling satiated or may prevent feeding on nutritious food sources, as has been seen in other taxa (McCauley and Bjornal, 1999;Xu et al., 2017;Egbeocha et al., 2018;Ory et al., 2018;de Barros et al., 2020). While large percentages of ingested MPs (64-92%) will likely be egested (Allen et al., 2017;Hankins et al., 2018;Hankins et al., 2021) by coral polyps, microplastic exposure has been shown to impact feeding, stress response, immune system, coralhost signaling, zooxanthellae photosynthetic performance, growth, and can cause bleaching and tissue necrosis (Chapron et al., 2018, Tang et al., 2018, Axworthy and Padilla-Gamiño, 2019, Reichert et al., 2019, Syakti et al., 2019, Huang et al., 2021a, 2021b, Lanctôt et al., 2020, Hankins et al., 2021. ...
... The 3D model presented in Fig. 3a interpolates ingestion potential between 0.231 and 0.462 mm; the lower threshold is likely within this size range. Additionally, the lower threshold may be indicative of the MP sizes in which coral passively feed on MPs (Hankins et al., 2018;Axworthy and Padilla-Gamiño, 2019) suggesting that smaller MPs do not elicit a tactile response from the coral tentacles. ...
Article
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Coral reefs have been heavily impacted by anthropogenic stressors, such as global warming, ocean acidification, sedimentation, and nutrients. Recently, microplastics (MP) have emerged as another potential stressor that may also cause adverse impacts to coral. MP ingestion by scleractinian coral among four species, Acropora cervicornis, Montastraea cavernosa, Orbicella faveolata, and Pseudodiploria clivosa, was used to identify the relationship between calyx and MP size as it pertains to active coral ingestion. A range of MP sizes (0.231–2.60 mm) were offered to the coral species across a wide range of calyx sizes (1.33–4.84 mm). Laboratory data showed that as the mean calyx size increased, so too did the mean percent of ingestion with increasing MP size. From laboratory data, a logistic model was developed to extrapolate the range of MP sizes that can be actively ingested by coral species based on calyx size. The data and model presented here offer the first predictive approach that can be used to determine the range of MP sizes that have a high likelihood of being actively ingested by coral of various sizes, thus offering insight to possible impacts on scleractinian coral.
... Plastics are known to accumulate and persist longer in sediments than on land (Worm et al., 2017). With the global explosion of plastic pollution, there is evidence cnidarians are capable of ingesting microplastics which are known to release phthalates (Hall et al., 2015;Axworthy and Padilla-Gamiño, 2019;Rotjan et al., 2019;Deng et al., 2020). As a leachable compound from plastics, phthalates are one of the most frequently detected persistent organic pollutants in the environment (Gao and Wen, 2016). ...
Article
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Endocrine disruption is suspected in cnidarians, but questions remain how occurs. Steroid sex hormones are detected in corals and sea anemones even though these animals do not have estrogen receptors and their repertoire of steroidogenic enzymes appears to be incomplete. Pathways associated with sex hormone biosynthesis and sterol signaling are an understudied area in cnidarian biology. The objective of this study was to identify a suite of genes that can be linked to exposure of endocrine disruptors. Exaiptasia diaphana were exposed to nominal 20ppb concentrations of estradiol (E2), testosterone (T), cholesterol, oxybenzone (BP-3), or benzyl butyl phthalate (BBP) for 4 h. Eleven genes of interest (GOIs) were chosen from a previously generated EST library. The GOIs are 17β-hydroxysteroid dehydrogenases type 14 (17β HSD14) and type 12 (17β HSD12), Niemann-Pick C type 2 (NPC2), Equistatin (EI), Complement component C3 (C3), Cathepsin L (CTSL), Patched domain-containing protein 3 (PTCH3), Smoothened (SMO), Desert Hedgehog (DHH), Zinc finger protein GLI2 (GLI2), and Vitellogenin (VTG). These GOIs were selected because of functional associations with steroid hormone biosynthesis; cholesterol binding/transport; immunity; phagocytosis; or Hedgehog signaling. Quantitative Real-Time PCR quantified expression of GOIs. In silico modelling utilized protein structures from Protein Data Bank as well as creating protein structures with SWISS-MODEL. Results show transcription of steroidogenic enzymes, and cholesterol binding/transport proteins have similar transcription profiles for E2, T, and cholesterol treatments, but different profiles when BP-3 or BBP is present. C3 expression can differentiate between exposures to BP-3 versus BBP as well as exposure to cholesterol versus sex hormones. In silico modelling revealed all ligands (E2, T, cholesterol, BBP, and BP-3) have favorable binding affinities with 17β HSD14, 17β HSD12, NPC2, SMO, and PTCH proteins. VTG expression was down-regulated in the sterol treatments but up-regulated in BP-3 and BBP treatments. In summary, these eleven GOIs collectively generate unique transcriptional profiles capable of discriminating between the five chemical exposures used in this investigation. This suite of GOIs are candidate biomarkers for detecting transcriptional changes in steroidogenesis, gametogenesis, sterol transport, and Hedgehog signaling. Detection of disruptions in these pathways offers new insight into endocrine disruption in cnidarians.
... Allen et al. 2017, Reichert et al. 2018. The interaction between microplastics and coral involves ingestion (Allen et al. 2017, Axworthy & Padilla-Gamiño 2019, egestion (Reichert et al. 2018) and surface adhesion (Martin et al. 2019). Laboratory studies have demonstrated that microplastic exposure might adversely influence growth rate, health status and physiology of corals, with consequences for feeding behaviour, photosynthetic performance, skeletal calcification, tissue bleaching and necrosis (reviewed in Huang et al. 2021). ...
Article
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Microplastics pollution differentially impacts coral reef systems, by threatening corals physically, through physiological distress and by increasing diseases. However, most of the studies to date have focused on scleractinian corals. The present work reports for the first time the patterns of microplastic ingestion and adhesion by the alcyonacean Coelogorgia palmosa. Feeding and adhesion tests were carried out with various concentrations of polyethylene microbeads. Results showed a wide range of surface adhesion, ranging from 3 to 1573 microbeads per coral fragment, suggesting that adhesion driven by mucus is the main mechanism of microplastic trapping. Polyethylene was ingested by 60% of coral fragments, and the average number of ingested microbeads was much lower compared to scleractinian corals. Considering the ecological importance of soft corals in coral reef ecosystems, specific attention regarding microplastic pollution effects on this taxon is recommended.
... Therefore, the more permanent microplastic exposure may prepare the corals for additional short-term (heat) stress through the process of molecular frontloading (Barshis et al., 2013). Although the impact of microplastic on the feeding behavior of corals is not well understood yet (Allen et al., 2017;Axworthy and Padilla-Gamiño, 2019;Chapron et al., 2018), another potential explanation for better performance in the microplastic treatments could be higher heterotrophic feeding rates stimulated by the presence of microplastic particles. Higher energy reserves and heterotrophic capacity may lead to higher thermal tolerance and shorter recovery times after coral bleaching (Grottoli et al., 2006). ...
Article
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 (2.5–2500 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.
... Although the impact of microplastic on the feeding behavior of corals is not well understood yet (Allen et al., 2017;Axworthy and Padilla-Gamiño, 2019;Chapron et al., 2018), another potential explanation for better performance in the microplastic treatments could be higher heterotrophic . CC-BY-NC 4.0 International license available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. ...
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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