Responses of reef building corals to microplastic exposure

Pollution of marine environments with microplastic particles (i.e. plastic fragments <5 mm) has increased rapidly during the last decades. As these particles are mainly of terrestrial origin, coastal ecosystems such as coral reefs are particularly threatened. Recent studies revealed that microplastic ingestion can have adverse effects on marine invertebrates. However, little is known about its effects on small-polyp stony corals that are the main framework builders in coral reefs. The goal of this study is to characterise how different coral species I) respond to microplastic particles and whether the exposure might II) lead to health effects. Therefore, six small-polyp stony coral species belonging to the genera Acropora, Pocillopora, and Porites were exposed to microplastics (polyethylene, size 37–163 μm, concentration ca. 4000 particles L−1) over four weeks, and responses and effects on health were documented.

The study showed that the corals responded differentially to microplastics. Cleaning mechanisms (direct interaction, mucus production) but also feeding interactions (i.e. interaction with mesenterial filaments, ingestion, and egestion) were observed. Additionally, passive contact through overgrowth was documented. In five of the six studied species, negative effects on health (i.e. bleaching and tissue necrosis) were reported.

We here provide preliminary knowledge about coral-microplastic-interactions. The results call for further investigations of the effects of realistic microplastic concentrations on growth, reproduction, and survival of stony corals. This might lead to a better understanding of resilience capacities in coral reef ecosystems.

Jessica Reichert, Johannes Schellenberg, Patrick Schubert, Thomas Wilke, Environmental Pollution, Available online 13 November 2017, In Press

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Chemoreception drives plastic consumption in a hard coral

The drivers behind microplastic (up to 5 mm in diameter) consumption by animals are uncertain and impacts on foundational species are poorly understood. We investigated consumption of weathered, unfouled, biofouled, pre-production and microbe-free National Institute of Standards plastic by a scleractinian coral that relies on chemosensory cues for feeding. Experiment one found that corals ingested many plastic types while mostly ignoring organic-free sand, suggesting that plastic contains phagostimulents. Experiment two found that corals ingested more plastic that wasn’t covered in a microbial biofilm than plastics that were biofilmed. Additionally, corals retained ~ 8% of ingested plastic for 24 h or more and retained particles appeared stuck in corals, with consequences for energetics, pollutant toxicity and trophic transfer. The potential for chemoreception to drive plastic consumption in marine taxa has implications for conservation.

A. S. Allen, A. C. Seymour, D. Rittschof, Marine Pollution Bulletin, Volume 124, Issue 1, 15 November 2017, Pages 198-205

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Strandings of NE Atlantic gorgonians

Northeast coral gardens provide vital breeding and feeding habitats for fishes of conservation and commercial importance. Such habitats are increasingly at risk of destruction as a result of over fishing, ocean warming, acidification and marine litter.

A key cause for concern regarding the vulnerability of coral gardens to damage from any source is their slow growth rate, and thereby their ability to recover from damage. Hence protected areas are being put in place, which exclude the use of towed demersal fishing gear.

Citizen scientists observed that gorgonian coral (Pink Sea Fans) skeletons were stranding on beaches entangled in marine debris (sea fangles) across southwest England. Further, SCUBA divers reported that gorgonian corals were being caught up and damaged in lost fishing gear and other marine litter.

To determine the cause of the damage to coral gardens, sea fangles were collected and analysed.

The sea fangles were made up of a diverse range of litter from fishing and domestic sources, however, the majority comprised of fishing gear (P < 0.05).

Marine Protected Areas can protect coral gardens from direct fishing pressure, but risks still remain from ghost fishing pressure, demonstrating the need for sources of litter into the environment to be reduced and existing litter removed.

The EU Marine Strategy Framework Directive (MSFD) outlines targets for marine litter by 2020. This study highlights the importance of adhering to the MSFD and/or creating more ambitious regulation if the UK re-write existing legislation following BREXIT.

E.V. Sheehan, A. Rees, D. Bridger, T. Williams, J.M. Hall-Spencer, Biological Conservation, Volume 209, May 2017, Pages 482–487

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Distribution and biological implications of plastic pollution on the fringing reef of Mo’orea, French Polynesia

Plastic pollution has been recognized as a major pollutant of the open ocean, but the extent and impact of plastic pollution on the coral reef environment has yet to be fully understood. In this study, the distribution of both macro- (>5mm) and micro- plastic (<5mm) of a typical coral reef ecosystem— the fringing reef of an isolated South Pacific island, Mo’orea, French Polynesia—was quantified. During the course of the study, macroplastic was found on every beach on the island, and distribution of plastic was categorized by site type and the presence of Turbinaria oranata, a common macroalgae of Mo’orea. Microplastic (plastic pieces <5mm) was found in the water column of the fringing reef of the island, at a concentration of 0.74 plastic pieces per square meter. To test the impact on coral reef organisms of the plastic pollution found in the fringing reef, microplastic was exposed to a species of soft coral, Discosoma a laboratory setting. The resilience of Discosoma fluctuating temperatures and rising CO2 levels is well understood, but the effect of plastic pollution on Discosoma spp. and other corallimorphs has never before been analyzed. This study reports for the first time the ingestion of microplastic by the soft coral Discosoma spp. Positively buoyant and negatively buoyant microplastic were both ingested over different time frames. In addition, wild (not experimentally introduced) microplastic was found in the stomach cavity of the organism. These findings indicate that plastic debris are being ingested by Discosoma spp. and may impair the health of this prevalent coral reef organism.

Elizabeth Janice Connors, PeerJ Preprints 5:e2697v1, 5/01/2017

The article

Migration of nonylphenol from food-grade plastic is toxic to the coral reef fish species Pseudochromis fridmani

Nonylphenol (NP) is a non-ionic surfactant used extensively in industrial applications, personal care products, and many plastics. We exposed marine orchid dottybacks (Pseudochromis fridmani) for 48 h to either glass, Teflon, or two bags labeled as FDA food-grade polyethylene (PE1 and PE2) from different manufacturers. The PE2 bags leached high levels of NP into the contact water, which were taken up by the fish, and decreased short and long-term survival. Concentrations of NP that leached from the bags were consistent with 96 h LC50 values determined in this study, indicating NP is the likely toxic agent. Despite being similarly labeled, the NP concentrations that leached from the bags and the resultant toxicity to the fish varied dramatically between manufacturers. This study highlights that some plastics, labeled as food-safe, can be highly toxic to aquatic animals, and could pose a greater threat to humans than previously realized. This study also highlights risks for aquatic animals exposed to increasing quantities of plastic waste.

Heather J. Hamlin, Kathleen Marciano, Craig A. Downs, Chemosphere, Volume 139, Pages 223–228, November 2015

The article


Potential release of PCBs from plastic scientific gear to fringing coral reef sediments in the Gulf of Thailand

A status on environmental contamination of the coral reefs on the islands of Samui and Katen of the western part of the Gulf of Thailand was investigated with a preliminarily analysis of bottom sediment samples. Coral reef bed sediments were characterized as relatively uncontaminated by human activities in terms of selected metals and PCBs. Potential release of PCBs to the ambient seawater from scientific equipment made of plastic materials placed into the coral reef waters for an extended period was investigated because the sedimentary PCBs concentrations were very low in the region. Eight plastics – acrylic, mono cast nylon, polycarbonate, polyethylene, polypropylene, ivory and grey-colored polyvinyl chloride, and Teflon® – were subjected to leaching in seawater after being thoroughly washed with laboratory detergent and distilled water. All plastics were found to release PCBs at highly variable rates to seawater in the initial 60 days. Grey-colored PVC, Teflon, and polycarbonate after rinsing with n-hexane were found to release less than 50 ng PCBs/kg of plastics and they could therefore be used to make scientific equipment to be deployed on the relatively PCBs-free coral reef beds.

Gi Hoon Hong and al., Deep Sea Research Part II: Topical Studies in Oceanography, Volume 96, Pages 41–49, November 2013

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