Chemoreception drives plastic consumption in a hard coral

Unveiling the risk of marine litter and derelict fishing gear in remote coral reefs of the Andaman and Nicobar Islands, North Indian Ocean

An increasing amount of plastic litter and derelict fishing gear in the global oceans poses significant threats to corals and reef-associated marine biota. In this context, an underwater marine litter survey was conducted along the fringing coral reefs in the Andaman and Nicobar Islands- a remote archipelago in the Bay of Bengal, Northern Indian Ocean. The result revealed entanglement and smothering of coral colonies by plastic and derelict fishing gear. The survey recorded an average litter density of 0.42 ± 0.08 items/m2 (range: 0.23 ± 0.02 to 0.71 ± 0.09) and a mean mass of 138.61 ± 42.15 g/m2 (range: 70.17 ± 7.74 to 303.4 ± 2.55). Plastic was the most dominant litter (60.82 %) recorded in the reef environment. Derelict fishing gear made of plastic comprised 33.65 % of the total litter. Plastic Abundance Index (PAI), Hazardous Item Index (HII), and Clean Environment Index (CEI) were used to assess the ecological impact of marine litter. These indices highlighted the significant risks posed by marine litter to the coral reef environment. The finding helps to strengthen the assessment of marine litter in remote islands and underscores the urgent need for improved waste management, stricter regulations on the disposal of fishing gear, and effective removal of derelict fishing gear from the coral reef environments. Present study offers actionable insights for policymakers and stakeholders to prioritize interventions for managing marine litter to safeguard vulnerable coral reef systems.

Microplastic pollution in stony coral skeletons and tissues: A case study of accumulation and interrelationship in South Penghu Marine National Park, Taiwan Strait

Microplastics (MPs) pose a growing threat to coral reef ecosystems worldwide. However, data on MP contamination in coral reefs remain limited, hampering accurate ecological risk assessment. This study investigated MP contamination in coral reefs at South Penghu Marine National Park, analyzing 40 samples from 31 coral species. The average MP abundance was 0.32 ± 0.32 MPs/g wet weight, and the mean MP abundance in the coral tissues (0.26 ± 0.26 MPs/g ww) was significantly higher than that in the coral skeleton (0.08 ± 0.10 MPs/g ww). Most MPs were small (<1 mm: >60 %), fibrous (99.7 %), and primarily composed of rayon (59.8 %) and polyester (27.5 %). Significant correlations were found among MP abundance in whole corals, coral tissues, and coral skeletons. The correlation equation established in this study, linking coral skeleton, tissue, and whole corals, can facilitate a more comprehensive understanding of MP pollution level and its associated risks in coral reef environments. Notably, monofilament overgrowth was observed, highlighting the impact of nearby fisheries and recreational activities on MP contamination. These findings provide valuable field-based data on MP pollution levels and the associated risks to corals and offer a novel tool for assessing MP accumulation and potential risks in coral ecosystems.

Increasing microplastic concentrations have nonlinear impacts on the physiology of reef-building corals

The pollution of marine environments with plastics, particularly microplastic (MP, i.e., plastic particles <5 mm), is a major threat to marine biota, including corals. While the effects of MPs are increasingly well understood, knowledge of how different concentrations of naturally occurring MP mixtures affect reef-building corals is still limited. Therefore, we aimed to elucidate the relationship of MP concentrations and their effects on reef-building corals. For this, we exposed two reef-building coral species (Stylophora pistillata and Pocillopora verrucosa) in a 12-week experiment to MPs at a gradient of concentrations (0, 0.1, 1, 10, and 100 mg·L-1). Specifically, we examined effects on the coral host physiology (i.e., surface and volume growth, calcification, necrosis, and polyp activity), and the photosynthetic activity of the photosymbionts (i.e., effective and maximum quantum yield, maximum relative electron transport rate, minimum saturating irradiance, and light capture efficiency). To mimic natural conditions, we used a MP mixture consisting of six polymers in forms of fibers and fragments. Both coral species showed reduced growth rates, necrosis, lower polyp activity, and an upregulation of photosynthesis, which intensified with increasing MP concentrations. While the effects on the coral host mostly showed basic linear or nonlinear dose-response relationships, the effects on the photosymbionts revealed more complex nonlinear dose-response relationships, and photosynthesis was only upregulated after a species-specific threshold. We found that high and extreme pollution scenarios caused strong adverse effects on coral physiology, while current low to moderate concentrations had minor effects. Increasing concentrations had amplifying effects, likely due to the disproportionately higher frequency of entanglement, leading to more frequent direct contact and potential transfer of toxins or pathogens. These results suggest that corals can cope with current average pollution levels. However, they also highlight the need for measures to limit permanent increases of MP pollution to protect the health of coral reefs.

Exposure to polypropylene microplastics induces the upregulation of protein digestion-associated genes and microbiome reorganization in the octocoral Junceella squamata

Microplastics, a new type of pollutants found in coral reefs, have attracted increasing attention. However, most of the current research focuses on the scleractinian corals and few reports on Octocorallia. To reveal the impact of microplastic exposure on Octocorallia, we analyzed the transcriptional response of the coral hosts Junceella squamata along with changes to the diversity and community structure of its symbiotic bacteria following exposure to polystyrene microplastics. These results suggest that the microplastics have adverse impacts on nutrient metabolism and absorption in J. squamata. The symbiotic bacteria of J. squamata exhibited a clear response after exposure to microplastics, which may also reflect an adaptation mechanism of corals, and help to maintain the physiological function of coral symbiotic function under the exposure of microplastics. This study has revealed the impact of microplastic exposure on J. squamata, providing new insights for coral protection against the background of increased microplastics pollution.

Bisphenol A leachate from polystyrene microplastics has species-specific impacts on scleractinian corals

Plastic waste causes pervasive environmental contamination and can result in the release of harmful chemical leachates into marine ecosystems, especially as they fragment to smaller microplastics (<5 mm). The toxicity of commonly found polystyrene (PS) microplastics and associated bisphenol A (BPA) leachate to framework-building corals Pocillopora damicornis and Dipsastraea pallida was assessed through exposure experiments. Intermittent exposure over 14-days to 1) virgin PS, 2) preformulated PS with bound BPA (BPA-PS) and 3) leached BPA-PS (L-BPA-PS; simulating early stages of weathering) showed that microplastics void of leachable BPA had minimal effect on either coral species. However, BPA leachate had negative effects on the maximal photochemical yield (Fv/Fm) and tissue composition of P. damicornis fragments (e.g., decreased chlorophyll and protein compared to controls). Conversely, BPA leachate did not compromise tissues of D. pallida fragments. These results reveal that exposure to chemicals leaching out of microplastics can drive negative effects of microplastic exposure distinct from physical mechanisms due to ingestion alone, and that effects are species specific.

Microplastic pollution in tropical coral reef ecosystems from the coastal South China Sea and their impacts on corals in situ

Coral reefs possess extremely high ecological value in tropical and subtropical waters worldwide. Microplastics as emerging and pervasive pollutants pose a great threat to the health of coral ecosystems. However, in situ studies on microplastics pollution and its impacts in coral ecosystems globally are limited. The occurrence characteristics of microplastics in the environment mediums and reef-dwelling organisms were investigated in coral reef areas from the southern Hainan Island, and the impacts of microplastics on corals in situ were evaluated in this study. Average microplastics abundance was 9.48 items L-1 in seawater, 190.00 items kg-1 in sediment, 0.36 items g-1 in coral, 1.50 items g-1 in shellfish, 0.48 items g-1 in fish gill, and 1.71 items g-1 in fish gastrointestinal tract. The prevalent microplastics in the above samples were characterized as being less than 1000 µm in size, fibrous, and transparent, with predominant polymer types as polyethylene terephthalate, polypropylene, polyethylene, and rayon. The microplastic enrichment capacity of different corals varied (Pocillopora > Acropora > Sinularia). Notably, microplastics were more abundant on the surface of corals compared to their interiors, with distinct characteristics observed, including larger-sized (>500 µm) and fiber-shaped polyethylene terephthalate microplastics on the surface and smaller-sized (20-200 µm) fragmented polyethylene microplastics within coral interiors. Furthermore, the investigation showed species-specific impacts of microplastics on corals in situ, including photosynthetic activity of photosymbionts and antioxidant and immune activities of corals. Furthermore, the ecological risks of microplastics were minor across most environmental media in the studied areas, with exceptions in the bottom seawater and surface sediment of YLW, which exhibited extreme and medium risk levels, respectively. Coral risk levels were generally medium, except for dangerous levels in DDH and high levels in LHT. The potential sources of microplastics in the marginal reefs of southern Hainan Island were primarily tourism, residential, and fishing activities.

Possible sink of missing ocean plastic: Accumulation patterns in reef-building corals in the Gulf of Thailand

Individual coral polyps contain three distinct components-the surface mucus layer, tissue, and skeleton; each component may exhibit varying extent of microplastic (MP) accumulation and serve as a short- or long-term repository for these pollutants. However, the literature on MP accumulation in wild corals, particularly with respect to the different components, is limited. In this study, we investigated the adhesion and accumulation of MPs in four coral species, including both large (Lobophyllia sp. and Platygyra sinensis) and small (Pocillopora cf. damicornis and Porites lutea) polyp corals collected from Si Chang Island in the upper Gulf of Thailand. The results revealed that MP accumulation varied significantly among the four coral species and their components. Specifically, P. cf. damicornis exhibited the highest degree of accumulation (2.28 ± 0.34 particles g-1 w.w.) [Tukey's honestly significant difference (HSD) test, p < 0.05], particularly in their skeleton (52.63 %) and with a notable presence of high-density MPs (Fisher's extract test, p < 0.05). The most common MP morphotype was fragment, accounting for 75.29 % of the total MPs found in the coral. Notably, the majority of MPs were black, white, or blue, accounting for 36.20 %, 15.52 %, and 11.49 % of the samples, respectively. The predominant size range of MP particles was 101-200 μm. Nylon, polyacetylene, and polyethylene terephthalate (PET) were the prevalent polymer types, accounting for 20.11 %, 14.37 %, and 9.77 % of the identified samples, respectively. In the large polyp corals, while MP shapes, colors, and sizes exhibited consistent patterns, remarkable differences were noted in the polymer types across the three components. The findings of this study improve the understanding of MP accumulation and its fate in coral reef ecosystems, underscoring the need for further investigation into MP-accumulation patterns in reef-building corals worldwide.

Microplastics in coral from three Mascarene Islands, Western Indian Ocean

Little is known about microplastics (MPs) in corals from the Indian Ocean. We compared MP concentrations, morphotypes, size, colours, and polymer compositions in six coral genera from three remote Mascarene islands (Rodrigues, St. Brandon's Atoll, and Agalega) of the Republic of Mauritius, on a 1200 km transect located in the South Equatorial Current (SEC). The mean MP concentration was 0.78 n/g (53 % fibres) with no significant differences between islands. Polymers were polypropylene (78 %) and polyethylene (18 %). We conclude that the SEC's MP concentrations and compositions have homogenized over thousands of kilometres across the Indian Ocean. We discuss the lack of hazardous polyurethane MPs in coral samples given obvious sources on St Brandon. To the best of our knowledge, this study is the first to report on MPs in coral from the Western Indian Ocean and the Mascarene Islands providing a baseline for further research, monitoring, mitigation, and policy development.

Low incidence of microplastics in coral reefs of Kāne'ohe Bay, Hawai'i, USA

This study investigated microplastic and other micro-debris pollution in sediment, seawater, sea cucumbers, and corals from fringing and patch reefs in Kāne'ohe Bay, O'ahu, Hawai'i, USA. Microplastic pollution in Kāne'ohe Bay Bay was low compared to other tropical coral reefs. Microplastics were detected in sediments (29 %), sea cucumbers (9 %), and coral (0-2 %) samples but were not quantifiable. Seawater had quantifiable microplastic (< 0.5 mm) and macroplastic (> 0.5 mm) pollution, with mean concentrations ranging from 0.0061 to 0.081 particles m-3. Most particles detected in seawater samples were larger, floating plastic debris consisting mostly of polyethylene, polypropylene fragments, and fibers. Across the other matrices, the most detected particles were polyester, polypropylene, and cotton fibers. These results provide baseline data for this important coral reef ecosystem, and further monitoring is recommended to understand the seasonal and long-term trends in microplastic pollution and its potential future impacts.

Microplastic Leachate Negatively Affects Fertilization in the Coral Montipora capitata

Microplastic pollution is an emerging stressor of concern to coral reef ecosystems, which are already threatened by additional global and local level anthropogenic stressors. The effects of ingesting microplastics alone on corals have been well studied, but the effects of the chemical composition of these particles have been understudied. Many microplastic-associated chemicals are endocrine disrupters potentially posing a threat to organismal reproduction. Therefore, the goal of this study was to determine if differences exist between the effects of microplastics themselves and microplastic leachate on Montipora capitata fertilization due to changes in fatty acid quantity and composition. Assays were conducted two years in a row which exposed M. capitata gamete bundles to either one of four types of recently manufactured, virgin microspheres (nylon, polypropylene, high-density polyethylene, or low-density polyethylene) at three concentrations (50, 100, or 200 particles/L) or microplastic leachates, presumably including plastic additives from these microspheres. Gamete fertilization was not impacted by microplastic particles themselves, but some of the microplastic leachate treatments with the same polymer type significantly reduced fertilization rates for M. capitata. Additionally, a total of 17 fatty acids were seen in both years, but neither fatty acid quantity nor composition correlated with observed declines in fertilization. Instead, fertilization and fatty acid data independently varied by concentration and polymer type, likely due to the presence of different chemicals. This study is the first to directly test the toxicity of microplastic leachate to coral reproduction. These findings show that microplastic-associated chemicals are an important stressor affecting successful coral fertilization and fatty acid quantity and composition and provide evidence for the negative effects of microplastic leachate to coral reproduction. Thus, plastic additives could pose an additional threat to coral replenishment and persistence in coral reef ecosystems.

Microplastic pollution status in the coral reef ecosystems on the Southern and Western coasts of Sri Lanka during the Southwest monsoon

We investigated the microplastics (MP) abundance, characteristics and pollution severity in the six coral reef ecosystems along the southern and western coasts of Sri Lanka during the southwest monsoon. The small blue-coloured fibres dominated within coral reefs and reef environments. The average coral, surface water and surface sediment MP concentration were 806.64 ± 93.72 particles kg-1ww, 23.42 ± 5.01 particles m-3, and 54.11 ± 8.04 particles kg-1dw, respectively. Coral MP concentration was significantly correlated with surface water (r = 0.65) and surface sediments (r = 0.59) indicating that the reef environment was the source of coral MP enrichment. Coral MP concentration was spatially different (p < 0.05) which may likely be due to the changes in winds, waves, coral biology and plastic sources. MP Pollution Load Index indicated that low MP contamination hazard. Since the presence of MP often deteriorates coral's health, further investigations are necessary to understand the MP's effects on the health of coral reef ecosystems.

Chronic effects of exposure to polyethylene microplastics may be mitigated at the expense of growth and photosynthesis in reef-building corals

The causes of the physiological effects of microplastic pollution, potentially harming reef-building corals, are unclear. Reasons might include increased energy demands for handling particles and immune reactions. This study is among the first assessing the effects of long-term microplastic exposure on coral physiology at realistic concentrations (200 polyethylene particles L-1). The coral species Acropora muricata, Pocillopora verrucosa, Porites lutea, and Heliopora coerulea were exposed to microplastics for 11 months, and energy reserves, metabolites, growth, and photosymbiont state were analyzed. Results showed an overall low impact on coral physiology, yet species-specific effects occurred. Specifically, H. coerulea exhibited reduced growth, P. lutea and A. muricata showed changes in photosynthetic efficiency, and A. muricata variations in taurine levels. These findings suggest that corals may possess compensatory mechanisms mitigating the effects of microplastics. However, realistic microplastic concentrations only occasionally affected corals. Yet, corals exposed to increasing pollution scenarios will likely experience more negative impacts.

Toxicity effects and mechanism of micro/nanoplastics and loaded conventional pollutants on zooplankton: An overview

Micro/nanoplastics in aquatic environments is a noteworthy environmental problem. Zooplankton, an important biological group in aquatic ecosystems, readily absorb micro/nanoplastics and produce a range of toxic endpoints due to their small size. This review summarises relevant studies on the effects of micro/nanoplastics on zooplankton, including combined effects with conventional pollutants. Frequently reported adverse effects include acute/chronic lethal effects, oxidative stress, gene expression, energetic homeostasis, and growth and reproduction. Obstruction by plastic entanglement and blockage is the physical mechanism. Genotoxicity and cytotoxicity are molecular mechanisms. Properties of micro/nanoplastics, octanol/water partition coefficients of conventional pollutants, species and intestinal environments are important factors influencing single and combined toxicity. Selecting a wider range of micro/nanoplastics, focusing on the aging process and conducting field studies, adopting diversified zooplankton models, and further advancing the study of mechanisms are the outstanding prospects for deeper understanding of impacts of micro/nanoplastics on aquatic ecosystem.

Identifying potential high-risk zones for land-derived plastic litter to marine megafauna and key habitats within the North Atlantic

The pervasive use of plastic in modern society has led to plastic litter becoming ubiquitous within the ocean. Land-based sources of plastic litter are thought to account for the majority of plastic pollution in the marine environment, with plastic bags, bottles, wrappers, food containers and cutlery among the most common items found. In the marine environment, plastic is a transboundary pollutant, with the potential to cause damage far beyond the political borders from where it originated, making the management of this global pollutant particularly complex. In this study, the risks of land-derived plastic litter (LDPL) to major groups of marine megafauna - seabirds, cetaceans, pinnipeds, elasmobranchs, turtles, sirenians, tuna and billfish - and a selection of productive and biodiverse biogenic habitats - coral reefs, mangroves, seagrass, saltmarsh and kelp beds - were analysed using a Spatial Risk Assessment approach. The approach combines metrics for vulnerability (mechanism of harm for megafauna group or habitat), hazard (plastic abundance) and exposure (distribution of group or habitat). Several potential high-risk zones (HRZs) across the North Atlantic were highlighted, including the Azores, the UK, the French and US Atlantic coasts, and the US Gulf of Mexico. Whilst much of the modelled LDPL driving risk in the UK originated from domestic sources, in other HRZs, such as the Azores archipelago and the US Gulf of Mexico, plastic originated almost exclusively from external (non-domestic) sources. LDPL from Caribbean islands - some of the largest generators of marine plastic pollution in the dataset of river plastic emissions used in the study - was noted as a significant input to HRZs across both sides of the Atlantic. These findings highlight the potential of Spatial Risk Assessment analyses to determine the location of HRZs and understand where plastic debris monitoring and management should be prioritised, enabling more efficient deployment of interventions and mitigation measures.

First recorded presence of anthropogenic fly-ash particles in coral skeletons

Fly-ash particles formed during industrial fossil-fuel combustion show a globally observed rapid increase in concentration within natural archives post-1950 and have been proposed as a marker for the Anthropocene Epoch. Here, we present the first record of fly-ash particles incorporated into coral skeletons. Particles are present in Mediterranean corals between CE 1957 and 1992 at concentrations of 8-30 g-1 coral, mirroring the period of increased industrial activity in the area, and corroborating with spheroidal carbonaceous particle (SCP) records globally. The findings have important implications for the use of SCPs as markers in natural archives. With the exception of microplastics, this is the first evidence of particulate contamination in corals collected from natural environments. Further research is needed to understand incorporation pathways into coral skeletons, any subsequent ecotoxicological impact of contaminants, and the influence on overall coral health globally.

Physical and cellular impact of environmentally relevant microplastic exposure on thermally challenged Pocillopora damicornis (Cnidaria, Scleractinia)

Microplastic pollution is an increasing threat to coral reefs, which are already strongly challenged by climate change-related heat stress. Although it is known that scleractinian corals can ingest microplastic, little is known about their egestion and how microplastic exposure may impair corals at physiological and cellular levels. In addition, the effects of microplastic pollution at current environmental concentration have been little investigated to date, particularly in corals already impacted by heat stress. In this study, the combined effects of these environmental threats on Pocillopora damicornis were investigated from a physical and cellular perspective. Colonies were exposed to three concentrations of polyethylene microplastic beads (no microplastic beads: [No MP], 1 mg/L: [Low MP]; 10 mg/L: [High MP]), and two different temperatures (25 °C and 30 °C) for 72 h. No visual signs of stress in corals, such as abnormal mucus production and polyp extroflection, were recorded. At [Low MP], beads adhered to colonies were ingested but were also egested. Moreover, thermally stressed colonies showed a lower adhesion and higher egestion of microplastic beads. Coral bleaching was observed with an increase in temperature and microplastic bead concentration, as indicated by a general decrease in chlorophyll concentration and Symbiodiniaceae density. An increase in lipid peroxidation was measured in colonies exposed to [Low MP] and [High MP] and an up-regulation of stress response gene hsp70 was observed due to the synergistic interaction of both stressors. Overall, our findings showed that heat stress still represents the main threat to P. damicornis, while the effect of microplastics on coral health and physiology may be minor, especially at control temperature. However, microplastics could exacerbate the effect of thermal stress on cellular homeostasis, even at [Low MP]. While reducing ocean warming is critical for preserving coral reefs, effective management of emerging threats like microplastic pollution is equally essential.

Occurrence of phthalic acid esters (PAEs) and active pharmaceutical ingredients (APIs) in key species of anthozoans in Mediterranean Sea

The Mediterranean Sea's biodiversity is declining due to climate change and human activities, with plastics and emerging contaminants (ECs) posing significant threats. This study assessed phthalic acid esters (PAEs) and active pharmaceutical ingredients (APIs) occurrence in four anthozoan species (Cladocora caespitosa, Eunicella cavolini, Madracis pharensis, Parazoanthus axinellae) using solid phase microextraction (SPME) and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). All specimens were contaminated with at least one contaminant, reaching maximum values of 57.3 ng/g for the ∑PAEs and 64.2 ng/g (wet weight) for ∑APIs, with dibutyl phthalate and Ketoprofen being the most abundant. P. axinellae was the most contaminated species, indicating higher susceptibility to bioaccumulation, while the other three species showed two-fold lower concentrations. Moreover, the potential adverse effects of these contaminants on anthozoans have been discussed. Investigating the impact of PAEs and APIs on these species is crucial, given their key role in the Mediterranean benthic communities.

Feeding responses of reef-building corals provide species- and concentration-dependent risk assessment of microplastic

The negative impacts of microplastic on reef-building corals are often attributed to the feeding responses to these particles. Although reactions to and ingestion of microplastic are frequently reported, a quantitative comparison to natural particles and of the factors influencing these responses is largely missing. Thus, this study aims to compare the feeding rates of corals to microplastic and natural particles, considering factors influencing these responses. Specifically, we I) studied the feeding responses of corals to microplastic, natural food, and non-food particles, II) examined the influence of biotic factors (i.e., biofilm on the particles and presence of natural food), III) evaluated species-specific differences in feeding responses to microplastic particles, and IV) applied a toxicodynamic model for species- and concentration-dependent risk assessments. We assessed the feeding responses of 11 coral species, spanning different life-history strategies and growth forms in experimental feeding trials. The results showed that the feeding responses of corals to microplastic differ from those to naturally occurring particles. Reactions to microplastic and natural food occurred equally often, while sand was more frequently rejected. Yet, the ingestion process was much more selective, and microplastic was ingested less frequently than natural food. The presence of a biofilm and natural food had activating effects on the feeding behavior of the corals on microplastic. Generally, coral species that exhibit a higher degree of heterotrophic feeding also reacted more often to microplastic. The species- and concentration-dependent toxicodynamic risk model built on these data reveals that most tested coral species are unlikely to be at risk under present environmental concentration levels. However, highly heterotrophic feeders, such as Blastomussa merleti, or generally vulnerable species, such as Pocillopora verrucosa, need special consideration. These findings help to better evaluate the responses of corals to microplastic and their risk in an increasingly polluted ocean.

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.

Microplastic pollution: a review of techniques to identify microplastics and their threats to the aquatic ecosystem

Microplastics (MPs), small synthetic particles, have emerged as perilous chemical pollutants in aquatic habitats, causing grave concerns about their disruptive effects on ecosystems. The fauna and flora inhabiting these specific environments consume these MPs, unwittingly introducing them into the intricate web of the food chain. In this comprehensive evaluation, the current methods of identifying MPs are amalgamated and their profound impacts on marine and freshwater ecosystems are discussed. There are many potential risks associated with MPs, including the dangers of ingestion and entanglement, as well as internal injuries and digestive obstructions, both marine and freshwater organisms. In this review, the merits and limitations of diverse identification techniques are discussed, including spanning chemical analysis, thermal identification, and spectroscopic imaging such as Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and fluorescent microscopy. Additionally, it discusses the prevalence of MPs, the factors that affect their release into aquatic ecosystems, as well as their plausible impact on various aquatic ecosystems. Considering these disconcerting findings, it is imperative that appropriate measures should be taken to assess the potential risks of MP pollution, protect aquatic life and human health, and foster sustainable development.

Microplastic trapping efficiency and hydrodynamics in model coral reefs: A physical experimental investigation

Coastal ecosystems, such as coral reefs, are vulnerable to microplastic pollution input from proximal riverine and shoreline sources. However, deposition, retention, and transport processes are largely unevaluated, especially in relation to hydrodynamics. For the first time, we experimentally investigate the retention of biofilmed microplastic by branching 3D printed corals (staghorn coral Acropora genus) under various unidirectional flows (U = {0.15, 0.20, 0.25, 0.30} ms-1) and canopy densities (15 and 48 corals m-2). These variables are found to drive trapping efficiency, with 79-98% of microplastics retained in coral canopies across the experimental duration at high flow velocities (U = 0.25-0.30 ms-1), compared to 10-13% for the bare bed, with denser canopies retaining only 15% more microplastics than the sparse canopy at highest flow conditions (U = 0.30 ms-1). Three fundamental trapping mechanisms were identified: (a) particle interception, (b) settlement on branches or within coral, and (c) accumulation in the downstream wake region of the coral. Corresponding hydrodynamics reveal that microplastic retention and spatial distribution is modulated by the energy-dissipative effects of corals due to flow-structure interactions reducing in-canopy velocities and generating localised turbulence. The wider ecological implications for coral systems are discussed in light of the findings, particularly in terms of concentrations and locations of plastic accumulation.

Do coral reefs act as sinks for microplastics?

Microplastic (MP) pollution has been detected in coral reefs, raising concerns regarding its global impact. Although they cover a small portion (<1%) of the total area of the world's oceans, coral reefs are geological and biological structures that trap MPs and disproportionately enhance their accumulation. In this review, we attempted to understand how coral reefs act as short- and long-term sinks for MPs. We describe five characteristics that lead to the enrichment of microplastics in coral reefs: 1) adhesion on reef-building corals at distinct depths; 2) ingestion by reef organisms (e.g., suspension feeders, such as sponges, ascidians, and corals), bioconcentration, and formation of short-term (i.e., years to decades) biological sinks for MPs; 3) formation of long-term (i.e., centuries) MP sinks in coral skeletons and unconsolidated subsurface sediments; 4) reduction of sediment resuspension and seafloor turbulent kinetic energy by complex marine forest architecture that reduces bottom shear stress, facilitates the retention, and deposition of small (<0.5 mm) and high-density floating MPs; and 5) diagenesis of Anthropocene sedimentary rocks containing MPs. We estimate that reef processes may remove more than 10% of floating MPs in shallow tropical waters yearly. Statistical results show that microplastic abundance for reef-building corals are higher than values found in reef sediments and especially in seawater. Moreover, pellets, films, foams and mainly fragments and fibers have been found. These field-based data support our hypothesis of sinks in the reef sediments and organisms. We highlight the role of these seascapes in the interception of MPs as traps and sinks in reef sediments, biota, and carbonate frameworks. As coral reefs are prone to MP accumulation and can become pollution hotspots, global initiatives are necessary to conserve these rich ecosystems and prevent rapidly increasing plastic pollution.

Microplastics in river sediment: Chronic exposure of the amphipod Gammarus fossarum to polyethylene terephthalate in a microcosm

Microplastics constitute a form of particulate matter in aquatic environments, where they are a widespread pollutant. The broad range of particle sizes facilitates interactions with diverse species assemblages. Exposure to microplastics can negatively impact organisms, but similar effects also arise from exposure to naturally occurring particles, such as increased oxidative stress. It therefore remains uncertain, what effects are specific to microplastic particles, and how these effects manifest as a consequence of chronic exposure. Here we show in microcosm experiments that long-term exposure (111 days) to irregularly shaped polyethylene terephthalate (PET) fragments (10-400 µm) added to riverine sediments did not negatively impact the amphipod Gammarus fossarum's group size, and oxygen consumption, and minimally affected proteome composition. We found that these results were consistent for male and female specimens when exposed to an environmentally relevant concentration (0.004% of sediment dry weight; dw) and an environmentally less realistic one (4% dw). In female specimens' whole proteomes, we identified two highly differentially abundant proteins, which have been associated with an organism's response to xenobiotics. We conclude that in this sentinel species exposure to PET microplastic fragments mixed into the sediment does not elicit significant stress, even at concentrations exceeding current exposure levels in the environment.

The role of microbe-microplastic associations in marine Nematode feeding behaviors

Fauna across many taxa and trophic levels have been shown to consume microplastics (MPs) in experiments, providing evidence that supports field-based gut content assessments. Multiple explanations exist regarding why fauna consume MPs, one of which posits that microbial growth on MPs may facilitate faunal ingestion. However, laboratory assessments on the reasons why MPs are consumed remain limited. Here, we assessed if the presence of microbes on MPs altered marine nematode feeding behaviors across current and potential future concentrations of MPs in a local system. We used a microcosm experiment in which field-collected sediment was spiked with bacterially treated or untreated fluorescent plastic microbeads (1.0-5.0 μm) in concentrations of 102, 104, and 106 per microcosm, representing local and potential future concentrations of MPs. Ingestion by the dominant interstitial fauna was investigated after 0, 3, and 7 days using bright field microscopy. Nematodes were the only fauna across microcosms that consumed MPs, but this consumption was variable and there were no apparent trends across exposure time, bacterial treatment, or MP concentration. There were also no genera- or feeding-type-specific trends in the number of MPs consumed, though four of the top five nematode genera that consumed MPs were pollution-tolerant genera. Our study demonstrates that microbe-MP associations do not drive marine nematodes to eat MPs, especially at local field concentrations. While there were no trends across any of the nematode genera in our study, we recognize that unrealistic MP concentrations in other studies may provide alternative explanations for nematode consumption of MPs.

Contamination of microplastics in tropical coral reef ecosystems of Sri Lanka

Microplastics (MPs) in different marine compartments are a global concern. This study investigated the abundance, distribution, and characteristics of microplastics from ten coral reef ecosystems in Sri Lanka, a non-quantified threat for some context. Microplastics were isolated and quantified in terms of abundance, shape, size, color, and polymer type with average abundances 546.7 ± 170.3 items kg-1, 9.8 ± 7.6 items m-3, and 46.3 ± 29.7 items kg-1 in corals, water, and sediments respectively. The most dominant microplastic type was blue, LDPE fibres. Acropora exhibited the highest amount. The significant differences in average microplastic abundances among corals suggest that they are capable of enriching microplastics depending on species-specific characteristics. Similar microplastic characteristics in corals and reef environment indicate that corals may have enriched microplastics from surface water and surface sediments. Microplastics being ubiquitous in selected reefs highlights the importance of coral reefs as a long-term microplastic sink in the ocean, contributing to the missing plastic phenomena.

The microscopic threat with a macroscopic impact: Microplastics along the southeast Florida reef tract

Microplastics decrease oceanic water quality and negatively impact marine life. This research quantified and classified marine plastic pollution along the Southeast Florida Reef Tract (SEFRT) to estimate the risk of microplastic damage to corals in this region. Surface and bottom water samples were collected at seven sites along the SEFRT over the course of six months and were analyzed for microplastic content. FTIR spectrophotometry was used to evaluate microplastic composition. Overall, seven plastic polymers were found across a total of 1204 microplastic items. Five contaminants were also identified, indicating that microplastics may be congregators of these hazardous contaminants. Significantly more total plastics were found in surface samples than in bottom samples, but plastic quantities were not significantly different when month, depth, and location were combined. Plastics were determined to have entered the ocean from multiple sources; in order to protect vulnerable reef ecosystems in this area, a two-factor approach is necessary to halt the release of microplastics into the ocean, including widespread plastic clean-up efforts and improvements to plastic waste management.

Microplastic as an invisible threat to the coral reefs: Sources, toxicity mechanisms, policy intervention, and the way forward

Microplastic (MP) pollution waste is a global macro problem, and research on MP contamination has been done in marine, freshwater, and terrestrial ecosystems. Preventing MP pollution from hurting them is essential to maintaining coral reefs' ecological and economic benefits. However, the public and scientific communities must pay more attention to MP research on the coral reef regions' distribution, effects, mechanisms, and policy evaluations. Therefore, this review summarizes the global MP distribution and source within the coral reefs. Current knowledge extends the impacts of MP on coral reefs, existing policy, and further recommendations to mitigate MPs contamination on corals are critically analyzed. Furthermore, mechanisms of MP on coral and human health are also highlighted to pinpoint research gaps and potential future studies. Given the escalating plastic usage and the prevalence of coral bleaching globally, there is a pressing need to prioritize research efforts on marine MPs that concentrate on critical coral reef areas. Such investigations should encompass an extensive and crucial understanding of the distribution, destiny, and effects of the MPs on human and coral health and the potential hazards of those MPs from an ecological viewpoint.

Distribution and risk assessment of microplastics in typical ecosystems in the South China Sea

Microplastic pollution in the marine environment has attracted worldwide attention. The South China Sea is considered a hotspot for microplastic pollution due to the developed industries and high population density around the South China Sea. The accumulation of microplastics in ecosystems can adversely affect the health of the environment and organisms. This paper reviews the recent microplastic studies conducted in the South China Sea, which novelty summarizes the abundance, types, and potential hazards of microplastics in coral reef ecosystems, mangrove ecosystems, seagrass bed ecosystems, and macroalgal ecosystems. A summary of the microplastic pollution status of four ecosystems and a risk assessment provides a more comprehensive understanding of the impact of microplastic pollution on marine ecosystems in the South China Sea. Microplastic abundances of up to 45,200 items/m³ were reported in coral reef surface waters, 5738.3 items/kg in mangrove sediments, and 927.3 items/kg in seagrass bed sediments. There are few studies of microplastics in the South China Sea macroalgae ecosystems. However, studies from other areas indicate that macroalgae can accumulate microplastics and are more likely to enter the food chain or be consumed by humans. Finally, this paper compared the current risk levels of microplastics in the coral reef, mangrove, and seagrass bed ecosystems based on available studies. Pollution load index (PLI) ranges from 3 to 31 in mangrove ecosystems, 5.7 to 11.9 in seagrass bed ecosystems, and 6.1 to 10.2 in coral reef ecosystems, respectively. The PLI index varies considerably between mangroves depending on the intensity of anthropogenic activity around the mangrove. Further studies on seagrass beds and macroalgal ecosystems are required to extend our understanding of microplastic pollution in marine environments. Recent microplastic detection in fish muscle tissue in mangroves requires more research to further the biological impact of microplastic ingestion and the potential food safety risks.

Microfiber Emissions from Functionalized Textiles: Potential Threat for Human Health and Environmental Risks

The growing worldwide population is directly responsible for the increased production and consumption of textile products. One of the key reasons for the generation of microfibers is the use of textiles and garment materials, which is expected to increase. The textile industry is responsible for the invisible pollution that is created by textile microfibers, which have been detected in marine sediments and organisms. The present review paper demonstrates that the microfibers discharged from functionalized textiles exhibit non-biodegradable characteristics and that a considerable proportion of them possess toxic properties. This is primarily attributed to the impact of textiles' material functionalization on their biodegradability. The potential for these microfibers, which are released from textiles that contain a variety of dyes, toxic chemicals, and nanomaterials, to pose a variety of health risks to both humans and other living organisms is discussed in this paper. In addition, this paper covers a wide variety of preventative and minimizing measures for reduction, which are discussed in terms of several phases ranging from sustainable production through the consumer, end of life, domestic washing, and wastewater treatment phases.

Impacts of marine debris on coral reef ecosystem: A review for conservation and ecological monitoring of the coral reef ecosystem

Coral reefs are the most spectacular underwater creation of nature. It enhances ecosystem functioning and marine biodiversity while also ensuring the livelihood of millions of coastal communities worldwide. Unfortunately, marine debris poses a serious threat to ecologically sensitive reef habitats and their associated organisms. Over the past decade, marine debris has been regarded as a major anthropogenic threat to marine ecosystems and gained scientific attention around the globe. However, the sources, types, abundance, distribution, and potential consequences of marine debris on reef ecosystems are hardly known. The goal of this review is to provide an overview of the current status of marine debris in various reef ecosystems across the world, with special emphasis on its sources, abundance, distribution, species impacted, major categories, potential impacts and management strategies. Furthermore, the adhesion mechanisms of microplastics to coral polyps, diseases caused by microplastics and are also highlighted.

Macro- and microplastics as complex threats to coral reef ecosystems

The impacts of macroplastics (macro-), microplastics (MPs, <5mm), and nanoplastics (NPs, <100 nm) on corals and their complex reef ecosystems are receiving increased attention and visibility. MPs represent a major, contemporary, sustainability challenge with known and unknown effects on the ocean, and coral reef ecosystems worldwide. However, the fate and transport processes of macro-, MPs, and NPs and their direct and indirect impacts on coral reef ecosystems remains poorly understood. In this study, we verify and briefly summarize MPs distribution and pollution patterns in coral reefs from various geographical regions and discuss potential risks. The main interaction mechanisms show that MPs may substantially affect coral feeding performance, proper skeletal formation, and overall nutrition and, thus, there is an urgent need to address this rapidly growing environmental problem. From a management perspective, macro-, MPs, and NPs should, ideally, all be included in environmental monitoring frameworks, as possible, to aid in identifying those geographical areas that are most heavily impacted and to support future prioritization of conservation efforts. The potential solutions to the macro-, MP, and NP pollution problem include raising public awareness of plastic pollution, developing robust, environmental, conservation efforts, promoting a circular economy, and propelling industry-supported technological innovations to reduce plastic use and consumption. Global actions to curb plastic inputs, and releases of macro-, MP, and NP particles, and their associated chemicals, to the environment are desperately needed to secure the overall health of coral reef ecosystems and their inhabitants. Global scale horizon scans, gap analyses, and other future actions are necessary to gain and increase momentum to properly address this massive environmental problem and are in good accordance with several relevant UN sustainable development goals to sustain planetary health.

Transfer of knowledge from model organisms to evolutionarily distant non-model organisms: The coral Pocillopora damicornis membrane signaling receptome

With the ease of gene sequencing and the technology available to study and manipulate non-model organisms, the extension of the methodological toolbox required to translate our understanding of model organisms to non-model organisms has become an urgent problem. For example, mining of large coral and their symbiont sequence data is a challenge, but also provides an opportunity for understanding functionality and evolution of these and other non-model organisms. Much more information than for any other eukaryotic species is available for humans, especially related to signal transduction and diseases. However, the coral cnidarian host and human have diverged over 700 million years ago and homologies between proteins in the two species are therefore often in the gray zone, or at least often undetectable with traditional BLAST searches. We introduce a two-stage approach to identifying putative coral homologues of human proteins. First, through remote homology detection using Hidden Markov Models, we identify candidate human homologues in the cnidarian genome. However, for many proteins, the human genome alone contains multiple family members with similar or even more divergence in sequence. In the second stage, therefore, we filter the remote homology results based on the functional and structural plausibility of each coral candidate, shortlisting the coral proteins likely to have conserved some of the functions of the human proteins. We demonstrate our approach with a pipeline for mapping membrane receptors in humans to membrane receptors in corals, with specific focus on the stony coral, P. damicornis. More than 1000 human membrane receptors mapped to 335 coral receptors, including 151 G protein coupled receptors (GPCRs). To validate specific sub-families, we chose opsin proteins, representative GPCRs that confer light sensitivity, and Toll-like receptors, representative non-GPCRs, which function in the immune response, and their ability to communicate with microorganisms. Through detailed structure-function analysis of their ligand-binding pockets and downstream signaling cascades, we selected those candidate remote homologues likely to carry out related functions in the corals. This pipeline may prove generally useful for other non-model organisms, such as to support the growing field of synthetic biology.

Does microplastic exposure and sex influence shell selection and motivation in the common European hermit crab, Pagurus bernhardus?

Microplastics (<5 mm) are a threat to marine biodiversity however their effects on animal cognition and behaviour are unclear. We investigated whether microplastic exposure affects shell selection behaviour and motivation in the common European hermit crab, Pagurus bernhardus. Subjects were maintained for 5 days in tanks containing either: polyethylene microplastic spheres (n = 40), or no plastic (n = 40). They were then placed in low-quality shells and presented with an alternative high-quality shell. When they first touched the high-quality shell, the hermit crabs were startled using visual and aural stimuli. We recorded the post-startle latency to re-contact the high-quality shell, quantifying motivation to explore and acquire a better shell. Plastic-exposed females were more likely to select the high-quality shell than control females. As hypothesised, female hermit crabs had longer initial contact latencies, startle durations, and shell entry latencies than males. We also found an interaction effect on shell investigation duration: females from the control treatment spent longer investigating the high-quality shell compared to males. This was absent in the microplastic treatment with females behaving similar to males. This controlled study serves as a starting point to investigate the effects of microplastics and sex differences on behaviour when under predatory threat, and demonstrated sex dependent sensitivity to an environmental pollutant of global concern.

The neglected potential source of microplastics from daily necessities: A study on protective mobile phone cases

Microplastics (MPs) pollution has become a serious global environment problem. It is therefore of practical significance to investigate the MP pollution caused by using plastic materials on a daily basis. In this study, different protective mobile phone cases (PMPCs) were selected as a representative plastic commodity that are in contact with the human body for long periods to explore the generation and transportation of MPs during 3 months of actual use. The average abundances were 1122 particles cm^-2 on the PMPC and 314 particles cm^-2 on the palm, respectively. There were four main kinds of MPs produced during the use of different PMPCs, which indicated that waste plastics may be recycled and used as raw materials, resulting in a complex PMPC composition. The median sizes of MPs on the surfaces of PMPCs and palms were 28 and 32 µm, respectively, which were smaller than the sizes reported in other studies. The combined effect of ultraviolet ageing and friction was the main reason for MP generation during daily PMPC use. Based on the results of a fitted regression equation and Monte Carlo simulation, the sharply generation of MPs may occur when PMPC was used for approximately 33 days.

Boat paint and epoxy fragments - Leading contributors of microplastic pollution in surface waters of a protected Andaman bay

Plastic pollution is a growing concern even in India's remotest oceanic islands. To understand the extent of the problem in relatively undisturbed areas of the Andaman and Nicobar Islands, we nested a microplastic survey within a year-long meroplankton study in the protected bay of the Lohabarrack salt water crocodile sanctuary, that lies on the less populated west coast of South Andaman Island. Surveys recovered microplastics year-round, in 299 out of 300 samples. The average microplastic density in the protected bay was 0.45 ± 0.32 particles per m³. Densities were highest during the monsoon, peaking at 2.34 particles per m³. Marine coating fragments (boat paint and epoxy, 58%) dominated the plastic debris composition year-round, while fibre only amounted to 15%. Marine coating fragments were most frequently encountered during the pre-monsoon, while fibres and other miscellaneous debris grew in abundance during the monsoon and post-monsoon months. Marine coating fragments were eaten by arrow worms, gastropods, appendicularians and Lucifer shrimp, and constituted 7% of the arrow worm diet. Microplastic density and composition found in this west facing protected bay was in stark contrast to the previously published observations from the east facing, human dominated Port Blair bay, providing clear indication of sources and potential mitigation strategies. This is the first year-long record of ocean plastics from the Andaman Islands, India and it provides evidence of pollution by boat paint and epoxy particles, an often-overlooked component of microplastic pollution.

Environmental impact assessment of plastic waste during the outbreak of COVID-19 and integrated strategies for its control and mitigation

During the COVID-19 pandemic, many positive shifts have been observed in the ecosystem, with a significant decrease in the greenhouse gas emissions and air pollution. On the other hand, there were unavoidable negative shifts due to a surge in demand for plastic products such as food and groceries' delivery packaging, single-use plastics, medical and personal protective equipment to prevent transmission of COVID-19. Plastic pollution can be considered as a key environmental issue in world due to the huge footprints of plastics on natural ecosystems and public health. Herein, we presented an overview on the rise of plastic pollution during the COVID-19 pandemic. The potential sources of plastic waste during COVID-19 with its negative effects on the environment such as marine ecosystems and the global economics are highlighted. We also suggested some strategies and recommendations to tackle plastic leakages by applying feedstock recycling, sterilization, and with the use of biodegradable plastics that have become a sustainable alternative to fossil fuel plastics. Also, the importance of elevating public awareness and some recommendations to mitigate plastic generated during the pandemic has been addressed as well.

Divergent Forms of Pyroplastic: Lessons Learned from the M/V X-Press Pearl Ship Fire

In late May 2021, the M/V X-Press Pearl container ship caught fire while anchored 18 km off the coast of Colombo, Sri Lanka and spilled upward of 70 billion pieces of plastic or "nurdles" (∼1680 tons), littering the country's coastline. Exposure to combustion, heat, chemicals, and petroleum products led to an apparent continuum of changes from no obvious effects to pieces consistent with previous reports of melted and burned plastic (pyroplastic) found on beaches. At the middle of this continuum, nurdles were discolored but appeared to retain their prefire morphology, resembling nurdles that had been weathered in the environment. We performed a detailed investigation of the physical and surface properties of discolored nurdles collected on a beach 5 days after the ship caught fire and within 24 h of their arrival onshore. The color was the most striking trait of the plastic: white for nurdles with minimal alteration from the accident, orange for nurdles containing antioxidant degradation products formed by exposure to heat, and gray for partially combusted nurdles. Our color analyses indicate that this fraction of the plastic released from the ship was not a continuum but instead diverged into distinct groups. Fire left the gray nurdles scorched, with entrained particles and pools of melted plastic, and covered in soot, representing partial pyroplastics, a new subtype of pyroplastic. Cross sections showed that the heat- and fire-induced changes were superficial, leaving the surfaces more hydrophilic but the interior relatively untouched. These results provide timely and actionable information to responders to reevaluate cleanup end points, monitor the recurrence of these spilled nurdles, gauge short- and long-term effects of the spilled nurdles to the local ecosystem, and manage the recovery of the spill. These findings underscore partially combusted plastic (pyroplastic) as a type of plastic pollution that has yet to be fully explored despite the frequency at which plastic is burned globally.

Synthesized effects of medium-term exposure to seawater acidification and microplastics on the physiology and energy budget of the thick shell mussel Mytilus coruscus

Ocean acidification (OA) and microplastics (MPs) contamination are two results of human excises. In regions like estuarine areas, OA and MPs exposure are happening at the same time. The current research investigated the synthesized effects of OA and MPs exposure for a medium-term duration on the physiology and energy budget of the thick shell mussel Mytilus coruscus. Mussels were treated by six combinations of three MPs levels (0, 10 and 1000 items L^-1) × two pH levels (7.3, 8.1) for 21 d. As a result, under pH 7.3, clearance rate (CR), food absorption efficiency (AE), respiration rate (RR), and scope for growth (SFG) significantly decreased, while the fecal organic dry weight ratio (E) significantly increased. 1000 items L^-1 MPs led to decrease of CR, E, SFG and increase of AE under pH 8.1. Interactive effects from combination of pH and MPs were found in terms of CR, AE, E and RR, but not for SFG of M. coruscus.

Uptake of microplastics by the snakelocks anemone (Anemonia viridis) is commonplace across environmental conditions

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 = 32). 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 17.5 ± 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.

Plastics in the environment as potential threat to life: an overview

Plastics have become inevitable for human beings in their daily life. Million tons of plastic waste is entering in oceans, soil, freshwater, and sediments. Invasion of plastics in different ecosystems is causing severe problems to inhabitants. Wild animals such as seabirds, fishes, crustaceans, and other invertebrates are mostly effected by plastic entanglements and organic pollutants absorbed and carried by plastics/microplastics. Plastics can also be potentially harmful to human beings and other mammals. Keeping in view the possible harms of plastics, some mitigation strategies must be adopted which may include the use of bioplastics and some natural polymers such as squid-ring teeth protein. This review focuses on the possible sources of intrusion and fate of plastics in different ecosystems, their potential deleterious effects on wildlife, and the measures that can be taken to minimize and avoid the plastic use.

First detection of microplastics in reef-building corals from a Maldivian atoll

The presence of microplastics in the world's oceans and their effects on marine habitats are highly concerning. As suspension-feeders, corals are very exposed to microplastics, compromising the health of coral reef ecosystems. In this study we surveyed for the first time the presence of microplastics in Maldivian reef-building corals. Aiming to determine the influence of exposure and depth on microplastic distribution, analyses were carried out on 38 individuals belonging to three different species. 58% of the investigated colonies resulted contaminated with particles within the 25-150 μm size range. The maximum concentration was encountered in a Pocillopora verrucosa colony sampled from a shallow inner reef (8.9 particles/g of coral). No significant differences in microplastic concentration were observed between different depths, exposures, sites and species. Overall, this study confirmed microplastic presence in coral reefs of the Maldivian archipelago including foundation species.

Impact of polyethylene microplastics on coral Goniopora columna causing oxidative stress and histopathology damages

In recent years, the increase of microplastics in the sea exerted a negative impact on coral health. This study has been undertaken to analyze the impact of microplastics on corals. Here, Goniopora columna was exposed to different concentrations of polyethylene microplastics (PE-MP). The daily polyps length and adaptability were recorded. Analysis of the zooxanthellae density and antioxidant activity of coral was done after 1, 3, 5 and 7 days. Further tissue morphology and accumulation of PE-MP were analyzed. The results showed that PE-MP at different concentrations can be adsorbed on the surface of corals and enter inside corals after 7 days. PE-MP at different concentrations reduced polyps length, adaptability and cause the changes in the density of zooxanthellae to be the reason for unbalancing of corals. PE-MP at different concentrations reduced the superoxide dismutase (SOD) activity after exposure to 1 day. PE-MP increased the catalase (CAT) activity at 100 mg/L after exposure; even after reducing the concentration has the same effect. PE-MP at various concentrations increased the glutathione peroxidase (GPx) activity after exposure to 5 and 7 days. It also increased the glutathione transferase (GST) and glutathione (GSH) activity after exposure to 5 and 7 days. PE-MP at different concentrations increased the malondialdehyde (MDA) content after exposure from 1 to 7 days. Analysis of tissue morphology and tissue accumulation shows that different concentrations of PE-MP cause mesenteric atrophy, vacuole, and accumulation in the coral mesenteric. These results indicate that the PE-MP can impact the antioxidant system and hampers the function of enzymes responsible for detoxification of G. columna, increase lipid peroxide content and also cause tissue damage through accumulating in the coral mesenteric.

Interactions Between Plastic, Microbial Biofilms and Gammarus pulex: An Initial Investigation

There is increasing evidence that microbial biofilms which form on the surface of marine plastics can increase plastics palatability, making it more attractive to organisms. The same information, however, does not exist for freshwater systems. This study observed the response of the freshwater amphipod Gammarus pulex when exposed to 3 cm-diameter discs of biofilm-covered plastic, both alone and when presented alongside its natural food. G. pulex did not fragment or consume the plastic materials, and the presence of colonised plastic in the immediate environment did not alter the amount of time organisms spent interacting with their natural food. This study provides baseline information for virgin and microbially colonised low-density polyethylene and polylactic acid film. Further studies, with other types of plastic possessing different physical properties and with different microbial biofilm compositions are now required to build further understanding of interactions between plastic, microbial biofilms, and freshwater shredding invertebrates.

Characterization of anthropogenic marine macro-debris affecting coral habitat in the highly urbanized seascape of Mumbai megacity

Marine debris has become a major form of pollution and a serious ecosystem health concern. The present study evaluates the accumulation, origin, and fate of debris in intertidal coral habitats of Mumbai-one of the world's highly populated coastal cities on the west coast of India. Predominantly, seven hermatypic coral species belonging to seven genera and five families were identified and mainly represented by Pseudosidastrea, Porites, and Bernardpora. In terms of number, the mean density of marine debris was 1.60 ± 0.13 SE items/m², which is higher than the global average. The mean density of plastic debris was 1.46 ± 0.14 SE items/m². Approximately 9% of total coral colonies were in physical contact with debris, and 22% of these colonies showed visible signs of partial bleaching. Single use plastic bags and wrappers were dominant plastic debris. The study area was characterized as 'very poor cleanliness' according to the Beach Quality Indexes, which include the Clean Coast Index, General Index, and Hazardous Items Index. The numerical model indicates the influence of river discharge and probable areas of plastic accumulation with high tidal currents in this region, maneuvering the spatial advection of litter in the nearshore areas. Combined analysis of ground-truthing and model simulation implies that the possible contributing sources of litter were representatives of land-based and sea-originated. The overall results point to increasing anthropogenic stressors threatening coastal coral communities, including marine debris pollution. It is advocated to adopt an integrated coastal zone management approach supported by coordinated policy frameworks could guide the mitigation of the debris footprint in coastal environments.

Microplastic ingestion by coral as a function of the interaction between calyx and microplastic size

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.

Effects of extremely high concentrations of polystyrene microplastics on asexual reproduction and nematocyst discharge in the jellyfish Sanderia malayensis

Numerous studies have assessed the detrimental effects of microplastics (MPs) on aquatic invertebrates due to their ubiquitous and persistent nature. In this study, the toxic effects of MPs were examined on the polyp and ephyrae of the marine hydrozoan Sanderia malayensis. The jellyfish were exposed to different sizes (1-6 μm) of non-functionalized polystyrene microbeads at a concentration of 1 × 10⁴ particles mL^-1. The MPs randomly attached to the external and internal parts of the jellyfish body, and the longest MP attachment was 52 days during the depuration after initial exposure (for 24 h). Consistent seventeen-day exposure to MPs significantly reduced the asexual reproduction of the S. malayensis polyps. To assess if the MPs can stimulate nematocyst discharge in polyp and ephyrae stages via direct contact, they were exposed to particle sizes up to 430 μm. None of the MPs or their aggregates, including the 430 μm particles, induced nematocyst discharge. These results suggest that prolonged exposure to relatively high MP concentrations affects the early stages of jellies and provides evidence for the no effect on nematocyst discharge.

Microplastics: impacts on corals and other reef organisms

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.

Integrated toxicokinetic/toxicodynamic assessment modeling reveals at-risk scleractinian corals under extensive microplastics impacts

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.

No short-term effect of sinking microplastics on heterotrophy or sediment clearing in the tropical coral Stylophora pistillata

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.

Influence of Particle Size on Ecotoxicity of Low-Density Polyethylene Microplastics, with and without Adsorbed Benzo-a-Pyrene, in Clam Scrobicularia plana

This study investigated the ecotoxicological effects of differently sized (4–6 µm and 20–25 µm) low-density polyethylene (LDPE) microplastics (MPs), with and without adsorbed benzo-a-pyrene (BaP), in clam Scrobicularia plana. Biomarkers of oxidative stress (superoxide dismutase—SOD; catalase—CAT), biotransformation (glutathione-S-transferases—GST), oxidative damage (lipid peroxidation—LPO) and neurotoxicity (acetylcholinesterase—AChE) were analysed in gills and digestive glands at different time intervals for a total of 14 days of exposure. In order to have a better impact perspective of these contaminants, an integrated biomarker response index (IBR) and Health Index were applied. Biomarker alterations are apparently more related to smaller sized (4–6 µm) MPs in gills and to virgin LDPE MPs in the digestive gland according to IBR results, while the digestive gland was more affected by these MPs according to the health index.