Coral reefs are amongst the most biodiverse ecosystems on earth, but are significantly impacted by agricultural runoff. Despite herbicides being commonly detected in coastal waters, the possibility of herbicide accumulation in coral reef species has largely been overlooked. We investigate the accumulation of several herbicides in five species of coral reef invertebrates collected from ten sites along the Maputaland coast, South Africa. Multiple herbicide residues were detected in 95% of the samples, with total average concentrations across sites ranging between 25.2 ng g⁻¹ to 51.3 ng g⁻¹ dw. Acetochlor, alachlor and hexazinone were the predominant herbicides detected at all sites, with atrazine and simazine detected less frequently. Significant interactive effects were detected between sites nested in reef complex crossed with species, based on multiple and total herbicide concentrations. In general, multivariate herbicide concentrations varied significantly between species within and across most sites. Contrastingly, the concentrations of the different herbicides and that of total herbicide did not differ between conspecifics at most sites nested in their respective reef complexes. On average, highest total herbicide concentrations were measured in soft coral (Sarcophyton glaucum; 90.4 ± 60 ng g⁻¹ and Sinularia gravis; 42.7 ± 25 ng g⁻¹) and sponge (Theonela swinhoei; 39.0 ± 40 ng g⁻¹) species, while significantly lower concentrations were detected in hard corals (Echinopora hirsutissima; 10.5 ± 5.9 ng g⁻¹ and Acropora austera; 5.20 ± 4.5 ng g⁻¹) at most sites. Agricultural runoff entering the ocean via the uMfolozi-St Lucia Estuary and Maputo Bay are likely sources of herbicide contamination to coral reefs in the region. There is an urgent need to assess the long-term effects of herbicide exposure on coral reef communities.

In this study, the contamination levels and seasonal variation of 22 PFASs were investigated in coastal reef-building corals (n = 68) from the northern South China Sea (SCS) during wet and dry seasons. Perfluorohexane sulfonate (PFHxS) was the predominant PFASs in all coral samples, representing 43% of the total PFAS. Long-chain PFASs, as well as PFAS alternatives, were frequently detected above the MQL (>88%) but showed relatively low concentrations compared to short-chain PFASs in most species and seasons. Seasonal variation of PFAS concentrations were observed in branching corals, indicating that the accumulation of PFASs may be associated with coral morphological structures. Interspecies differences in PFAS levels agree well with different bioaccumulation potentials among coral species. Redundancy analysis (RDA) showed that seasonal factor and coral genus could partly influence PFAS concentrations in coral tissues. In summary, our study firstly reported the occurrence of PFASs in coral communities from the SCS and highlights the necessity for future investigations on more toxicity data for coral communities.

Microplastic ingestion has been widely documented in marine zooplankton, but the retention time of microplastics in their digestive gut are still poorly studied, especially among species from different climatic zones and marine habitats. This study evaluated the ingestion and gut retention time of four sizes of fluorescent microplastic beads (1.3, 7.3, 10.6, and 19.0 μm) in stage II naupliar larvae of nine barnacle species from different habitats (epibiotic on turtles, mangroves, coral reefs, and rocky shores) and climatic zones (subtropical/tropical and temperate). Microbeads were not lethal to all species (climatic zones/habitats) tested from the four sizes of non-fluorescent virgin microbeads (1.7, 6.8, 10.4 and 19.0 μm, each at concentrations 1, 10, 100, and 1000 beads mL⁻¹). Gut retention time of microplastic beads in barnacle naupliar larvae significantly increased with decreasing size. Microbeads resided in digestive tracts generally 3–4 times longer in rocky shore and coral reef barnacles than in muddy shore and epibiotic ones. However, species from different climatic zone did not differ in retention time. Our results suggested nauplius larvae from rocky shore and coral reef barnacles appear to be more susceptible to the impacts of longer retained microplastics (e.g., toxic chemicals present on the surface).

Swift degradation of the coral reef ecosystems urges the need to identify the reef decline drivers. Due to their widespread use, bioaccumulative and toxic characteristics, chlorinated organic compounds, such as chlorinated paraffins (CPs), are regarded as specific pollutants of concern. Yet little is known about the occurrence of CPs in the coral reef ecosystems. This study focuses on the short-chain chlorinated paraffins (SCCPs) and medium-chain chlorinated paraffins (MCCPs). Their distribution and congener pattern were investigated in the water-SPM-sediment system and in the corals of the Larak coral reef for the first time. Chlorinated paraffins were detected in all the coral species. Their total loadings ranged from 42.1 to 178 ng g⁻¹ dw in coral tissue, from 6.0 to 144 ng g⁻¹dw in the skeleton, and from 55.0 to 240 ng g⁻¹dw in zooxanthellae. Soft corals were found to accumulate more CPs than Scleractinian corals. Zooxanthellae and mucus accumulated more CPs than tissue and skeleton. In most cases, congener group patterns were dominated by C₁₃ (for SCCPs) and C₁₇ (MCCPs) groups, respectively. The congener patterns of CPs altered to some extent between mucus and the remaining coral compartments. High loadings of CPs were detected in the skeleton of the bleached corals. Moreover, a significant negative correlation between the levels of CPs and the symbiodinium density was observed.

The anthropogenic marine debris, especially abandoned, lost or otherwise discarded Fishing Gear (ALDFG), represents a rising concern, because of its potential harmful impact on the marine animal forests. We carried out 13 km of video recordings, by means of a remotely operated vehicle, from 10 to 210 m depth, in an anthropised area of the Tyrrhenian Sea (Mediterranean Sea). This site, for its high ecological importance and biodiversity value, has been identified for the establishment of a new marine protected area (MPA). The aim of this paper was to assess marine litter abundance and its effects on the benthic fauna. The debris density, in the study area, ranged from 0.24 to 8.01 items/100 m2, with an average of 3.49 (±0.59) items/100 m2. The derelict fishing gear, mainly fishing lines, were the main source of marine debris, contributing 77.9% to the overall litter. The impacts of debris on the benthic fauna were frequently recorded, with 28.5% of the litter entangling corals and impacting habitats of conservation concern. These impacts were exclusively caused by the derelict fishing gear (91.2% by longlines), and the highest percentage (49.1%) of ALDFG causing impacts was observed from 41 to 80 m depth, in the coralligenous biocenosis. The results of the present study will help the fulfilment of “harm” monitoring, as recommended by the Marine Strategy Framework Directive (MSFD) and the UN Environment/MAP Regional Plan on the marine litter management in the Mediterranean Sea. Regarding the actions to reduce the derelict fishing gear, preventive measures are usually preferred instead of the extensive removals based on cost-effectiveness and sustainability. The establishment of a new MPA in the area could be a good solution to reduce ALDFG, resulting in the improvement of the ecological status of this coastal area.

The potential impacts of mining activities on tropical coastal ecosystems are poorly understood. In particular, limited information is available on the effects of metals on scleractinian corals which are foundation species that form vital structural habitats supporting other biota. This study investigated the effects of dissolved nickel and copper on the coral Acropora muricata and its associated microbiota. Corals collected from the Great Barrier Reef were exposed to dissolved nickel (45, 90, 470, 900 and 9050 μg Ni/L) or copper (4, 11, 32 and 65 μg Cu/L) in flow through chambers at the National Sea Simulator, Townsville, Qld, Australia. After a 96-h exposure DNA metabarcoding (16S rDNA and 18S rDNA) was undertaken on all samples to detect changes in the structure of the coral microbiome. The controls remained healthy throughout the study period. After 36 h, bleaching was only observed in corals exposed to 32 and 65 μg Cu/L and very high nickel concentrations (9050 μg Ni/L). At 96 h, significant discolouration of corals was only observed in 470 and 900 μg Ni/L treatments, the highest concentrations tested. While high concentrations of nickel caused bleaching, no changes in the composition of their microbiome communities were observed. In contrast, exposure to copper not only resulted in bleaching, but altered the composition of both the eukaryote and bacterial communities of the coral's microbiomes. Our findings showed that these effects were only evident at relatively high concentrations of nickel and copper, reflecting concentrations observed only in extremely polluted environments. Elevated metal concentrations have the capacity to alter the microbiomes which are inherently linked to coral health.

Previous aquaria-based experiments have shown dissolution and leaching of metals, especially copper (Cu), from the simulated sediment plumes generated during mining activities resulting in a pronounced increase of Cu contamination in the surrounding seawater. Metals are bioavailable to corals with food, through ingestion (particulate phase) and through tissue-facilitated transport (passive diffusion). With corals being particularly vulnerable to metal contamination, resuspension of metal-bearing sediments during mining activities represents an important ecological threat. This study was undertaken to evaluate the impact of acute copper exposure (LC50;96 h) on the survival of the cold-water octocoral Dentomuricea aff. meteor. The experimental design was divided in two stages. In stage one, a Cu range-finding toxicity test was performed using Cu dilutions in filtered seawater with concentrations of 0 (control); 60; 150; 250; 450; 600 μg/L. Coral mortality was investigated visually based on the percent surface area of tissue changing from natural yellow colour to black colour indicative of tissue necrosis and death. In stage two, we used the results obtained in the range-finding experiment, to define sub-lethal Cu exposure treatments and exposed D. meteor to Cu concentration of 0 (control); 50; 100; 150; 200; 250 μg/L for 96 h. The corals physical conditions were inspected daily and seawater conditions recorded. Corals were considered dead when all of their tissue turned black. The LC50 value was calculated with regression analysis following Probits methodology. Our results indicate that Cu LC50;96 h for the octocoral D. meteor is 137 μg/L.

About 140-year changes in the trace metals in Porites coral samples from two locations in the northern South China Sea were investigated. Results of PCA analyses suggest that near the coast, terrestrial input impacted behavior of trace metals by 28.4%, impact of Sea Surface Temperature (SST) was 19.0%, contribution of war and infrastructure were 14.4% and 15.6% respectively. But for a location in the open sea, contribution of War and SST reached 33.2% and 16.5%, while activities of infrastructure and guano exploration reached 13.2% and 14.7%. While the spatiotemporal change model of Cu, Cd and Pb in seawater of the north area of South China Sea during 1986–1997 were reconstructed. It was found that in the sea area Cu and Cd contaminations were distributed near the coast while areas around Sanya, Hainan had high Pb levels because of the well-developed tourism related activities.

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.

Oil pollution remains a prominent local hazard to coral reefs, but the sensitivity of some coral life stages to oil exposure remains unstudied. Exposure to ultraviolet radiation (UVR), ubiquitous on coral reefs, may significantly increase oil toxicity towards these critical habitat-forming taxa. Here we present the first data on the sensitivity of two distinct post-settlement life stages of the model coral species Acropora millepora to a heavy fuel oil (HFO) water accommodated fraction (WAF) in the absence and presence of UVR. Assessment of lethal and sublethal endpoints indicates that both 1-week-old and 2-month-old recruits (1-wo and 2-mo) were negatively affected by chronic exposures to HFO (7 and 14 days, respectively). Relative growth (1-wo and 2-mo recruits) and survival (1-wo recruits) at end of exposure were the most sensitive endpoints in the absence of UVR, with no effect concentrations (NEC) of 34.3, 5.7 and 29.3 μg L⁻¹ total aromatic hydrocarbons (TAH; ∑39 monocyclic- and polycyclic aromatic hydrocarbons), respectively. On average, UVR increased the negative effects by 10% for affected endpoints, and latent effects of exposure were evident for relative growth and symbiont uptake of recruits. Other sublethal endpoints, including maximum quantum yield and tissue colour score, were unaffected by chronic HFO exposure. A comparison of putative species-specific sensitivity constants for these ecologically relevant endpoints, indicates A. millepora recruits may be as sensitive as the most sensitive species currently included in oil toxicity databases. While the low intensity UVR only significantly increased the negative effects of the oil for one endpoint, the majority of endpoints showed trends towards increased toxicity in the presence of UVR. Therefore, the data presented here further support the standard incorporation of UVR in oil toxicity testing for tropical corals.