The dispersant Corexit 9500 and (dispersed) oil are lethal to coral endosymbionts.

Endosymbionts (Symbiodiniaceae) play a vital role in the health of corals. Seawater pollution can harm these endosymbionts and dispersants used during oil spill cleanup can be extremely toxic to these organisms. Here, we examined the impact of oil and a specific dispersant, Corexit-9500, on two representative endosymbionts - Symbiodinium and Cladocopium - from the Southwestern endemic coral Mussismilia braziliensis. The survival and photosynthetic potential of the endosymbionts decreased dramatically after exposure to the dispersant and oil by ~25 % after 2 h and ~50 % after 7 days. Low concentrations of dispersant (0.005 ml/l) and dispersed oil (Polycyclic Aromatic Hydrocarbons, 1132 µg/l; Total Petroleum Hydrocarbons, 595 µg/l) proved highly toxic to both Symbiodinium and Cladocopium. These levels triggered a reduction in growth rate, cell size, and cell wall thickness. After a few hours of exposure, cellular organelles were damaged or destroyed. These acute toxic effects underline the fragile nature of coral endosymbionts.

Contrasting effects of increasing dissolved iron on photosynthesis and O2 availability in the gastric cavity of two Mediterranean corals.

Iron (Fe) plays a fundamental role in coral symbiosis, supporting photosynthesis, respiration, and many important enzymatic reactions. However, the extent to which corals are limited by Fe and their metabolic responses to inorganic Fe enrichment remains to be understood. We used respirometry, variable chlorophyll fluorescence, and O2 microsensors to investigate the impact of increasing Fe(III) concentrations (20, 50, and 100 nM) on the photosynthetic capacity of two Mediterranean coral species, Cladocora caespitosa and Oculina patagonica. While the bioavailability of inorganic Fe can rapidly decrease, we nevertheless observed significant physiological effects at all Fe concentrations. In C. caespitosa, exposure to 50 nM Fe(III) increased rates of respiration and photosynthesis, while the relative electron transport rate (rETR(II)) decreased at higher Fe(III) exposure (100 nM). In contrast, O. patagonica reduced respiration, photosynthesis rates, and maximum PSII quantum yield (Fv/Fm) across all iron enrichments. Both corals exhibited increased hypoxia (<50 µmol O2 L-1) within their gastric cavity at night when exposed to 50 and 100 nM Fe(III), leading to increased polyp contraction time and reduced O2 exchange with the surrounding water. Our results indicate that C. caespitosa, but not O. patagonica, might be limited in Fe for achieving maximal photosynthetic efficiency. Understanding the multifaceted role of iron in corals' health and their response to environmental change is crucial for effective coral conservation.

Identification of tolerance levels on the cold-water coral Desmophyllum pertusum (Lophelia pertusa) from realistic exposure conditions to suspended bentonite, barite and drill cutting particles.

Cold-water coral (CWC) reefs are numerous and widespread along the Norwegian continental shelf where oil and gas industry operate. Uncertainties exist regarding their impacts from operational discharges to drilling. Effect thresholds obtained from near-realistic exposure of suspended particle concentrations for use in coral risk modeling are particularly needed. Here, nubbins of Desmophyllum pertusum (Lophelia pertusa) were exposed shortly (5 days, 4h repeated pulses) to suspended particles (bentonite BE; barite BA, and drill cuttings DC) in the range of ~ 4 to ~ 60 mg.l-1 (actual concentration). Physiological responses (respiration rate, growth rate, mucus-related particulate organic carbon OC and particulate organic nitrogen ON) and polyp mortality were then measured 2 and 6 weeks post-exposure to assess long-term effects. Respiration and growth rates were not significantly different in any of the treatments tested compared to control. OC production was not affected in any treatment, but a significant increase of OC:ON in mucus produced by BE-exposed (23 and 48 mg.l-1) corals was revealed 2 weeks after exposure. Polyp mortality increased significantly at the two highest DC doses (19 and 49 mg.l-1) 2 and 6 weeks post-exposure but no significant difference was observed in any of the other treatments compared to the control. These findings are adding new knowledge on coral resilience to short realistic exposure of suspended drill particles and indicate overall a risk for long-term effects at a threshold of ~20 mg.l-1.

Interpreting Risk from Sunscreens in the Marine Environment.

Recent and pending bans in specific jurisdictions of some organic ultraviolet (UV) filters have resulted in significant concern and controversy over the potential impacts of these contaminants in the marine environment. Organic UV filters have been quantified in the aquatic environment as contaminants in water, sediments, and the tissues of aquatic organisms. The limited available laboratory studies on the toxicity of UV filters to keystone marine species such as reef-building corals describe a wide variety of impacts, from significant acute effects to no observed effects. However, interpretation of results is complicated by differences in methodology, and exposures to single agents in vitro may not reflect the effects of longer exposure to finished sunscreens containing UV filters in combination with numerous other chemicals. Relatively short-term observations of laboratory effects thus may not translate to real-life field conditions, where organisms may be subject to the effects of long-term chronic exposure to UV filters as well as other environmental contaminants and stressors. The lack of current understanding of the full impacts of UV filters, both in the laboratory and in the environment, represents a significant challenge in interpreting the environmental risk associated with the widespread use of sunscreens.

Ultraviolet radiation protection potentials of Methylene Blue for human skin and coral reef health.

Methylene blue (MB) is a century-old medicine, a laboratory dye, and recently shown as a premier antioxidant that combats ROS-induced cellular aging in human skins. Given MB's molecular structure and light absorption properties, we hypothesize that MB has the potential to be considered as a sunscreen active for UV radiation protection. In this study, we tested the effects of MB on UVB ray-induced DNA double-strand breaks in primary human keratinocytes. We found that MB treatment reduced DNA damages caused by UVB irradiation and subsequent cell death. Next, we compared MB with Oxybenzone, which is the most commonly used chemical active ingredient in sunscreens but recently proven to be hazardous to aquatic ecosystems, in particular to coral reefs. At the same concentrations, MB showed more effective UVB absorption ability than Oxybenzone and significantly outperformed Oxybenzone in the prevention of UVB-induced DNA damage and the clearance of UVA-induced cellular ROS. Furthermore, unlike Oxybenzone, MB-containing seawater did not affect the growth of the coral species Xenia umbellata. Altogether, our study suggests that MB has the potential to be a coral reef-friendly sunscreen active ingredient that can provide broad-spectrum protection against UVA and UVB.

Multiple impacts of microplastics can threaten marine habitat-forming species.

Microplastics are recognised as a potential global threat to marine ecosystems, but the biological mechanisms determining their impact on marine life are still largely unknown. Here, we investigated the effects of microplastics on the red coral, a long-lived habitat-forming organism belonging to the Corallium genus, which is present at almost all latitudes from shallow-water to deep-sea habitats. When exposed to microplastics, corals preferentially ingest polypropylene, with multiple biological effects, from feeding impairment to mucus production and altered gene expression. Microplastics can alter the coral microbiome directly and indirectly by causing tissue abrasions that allow the proliferation of opportunistic bacteria. These multiple effects suggest that microplastics at the concentrations present in some marine areas and predicted for most oceans in the coming decades, can ultimately cause coral death. Other habitat-forming suspension-feeding species are likely subjected to similar impacts, which may act synergistically with climate-driven events primarily responsible for mass mortalities.

Effect of Louisiana sweet crude oil on a Pacific coral, Pocillopora damicornis.

Recent oil spill responses such as the Deepwater Horizon event have underscored the need for crude oil ecotoxicological threshold data for shallow water corals to assist in natural resource damage assessments. We determined the toxicity of a mechanically agitated oil-seawater mixture (high-energy water-accommodated fraction, HEWAF) of a sweet crude oil on a branched stony coral, Pocillopora damicornis. We report the results of two experiments: a 96 h static renewal exposure experiment and a "pulse-chase" experiment of three short-term exposure durations followed by a recovery period in artificial seawater. Five endpoints were used to determine ecotoxicological values: 1) algal symbiont chlorophyll fluorescence, 2) a tissue regeneration assay and a visual health metric with three endpoints: 3) tissue integrity, 4) tissue color, and 5) polyp behavior. The sum of 50 entrained polycyclic aromatic hydrocarbons (tPAH50) was used as a proxy for oil exposure. For the 96 h exposure dose response experiment, dark-adapted maximum quantum yield (Fv/Fm) of the dinoflagellate symbionts was least affected by crude oil (EC50 = 913 µg/L tPAH50); light-adapted effective quantum yield (EQY) was more sensitive (EC50 =  428 µg/L tPAH50). In the health assessment, polyp behavior (EC50 = 27 µg/L tPAH50) was more sensitive than tissue integrity (EC50 = 806 µg/L tPAH50) or tissue color (EC50 = 926 µg/L tPAH50). Tissue regeneration proved to be a particularly sensitive measurement for toxicity effects (EC50 = 10 µg/L tPAH50). Short duration (6-24 h) exposures using 503 µg/L tPAH50 (average concentration) resulted in negative impacts to P. damicornis and its symbionts. Recovery of chlorophyll a fluorescence levels for 6-24 h oil exposures was observed in a few hours (Fv/Fm) to several days (EQY) following recovery in fresh seawater. The coral health assessments for tissue integrity and tissue color were not affected following short-term oil exposure durations, but the 96 h treatment duration resulted in significant decreases for both. A reduction in polyp behavior (extension) was observed for all treatment durations, with recovery observed for the short-term (6-24 h) exposures within 1-2 days following placement in fresh seawater. Wounded and intact fragments exposed to oil treatments were particularly sensitive, with significant delays observed in tissue regeneration. Estimating ecotoxicological values for P. damicornis exposed to crude oil HEWAFs provides a basis for natural resource damage assessments for oil spills in reef ecosystems. These data, when combined with ecotoxicological values for other coral reef species, will contribute to the development of species sensitivity models.

Cold-water coral (Lophelia pertusa) response to multiple stressors: High temperature affects recovery from short-term pollution exposure.

There are numerous studies highlighting the impacts of direct and indirect stressors on marine organisms, and multi-stressor studies of their combined effects are an increasing focus of experimental work. Lophelia pertusa is a framework-forming cold-water coral that supports numerous ecosystem services in the deep ocean. These corals are threatened by increasing anthropogenic impacts to the deep-sea, such as global ocean change and hydrocarbon extraction. This study implemented two sets of experiments to assess the effects of future conditions (temperature: 8 °C and 12 °C, pH: 7.9 and 7.6) and hydrocarbon exposure (oil, dispersant, oil + dispersant combined) on coral health. Phenotypic response was assessed through three independent observations of diagnostic characteristics that were combined into an average health rating at four points during exposure and recovery. In both experiments, regardless of environmental condition, average health significantly declined during 24-hour exposure to dispersant alone but was not significantly altered in the other treatments. In the early recovery stage (24 hours), polyp health returned to the pre-exposure health state under ambient temperature in all treatments. However, increased temperature resulted in a delay in recovery (72 hours) from dispersant exposure. These experiments provide evidence that global ocean change can affect the resilience of corals to environmental stressors and that exposure to chemical dispersants may pose a greater threat than oil itself.

Energy metabolism enzymes inhibition by the combined effects of increasing temperature and copper exposure in the coral Mussismilia harttii.

The combined effects of exposure to increasing temperature and copper (Cu) concentrations were evaluated in the zooxanthellate scleractinian coral Mussismilia harttii. Endpoints analyzed included activity of enzymes involved in glycolysis (pyruvate kinase, PK; lactate dehydrogenase, LDH), Krebs cycle (citrate synthase, CS; isocitrate dehydrogenase; IDH), electron transport chain (electron transport system, ETS) and pentose phosphate pathway (glucose-6-phosphate dehydrogenase, G6PDH). Coral polyps were kept under control conditions (25.0 ±â€¯0.1 °C; 2.9 ±â€¯0.7 µg/L Cu) or exposed to combined treatments of increasing temperature (26.6 ±â€¯0.1 °C and 27.3 ±â€¯0.1 °C) and concentrations of dissolved Cu (5.4 ±â€¯0.9 and 8.6 ±â€¯0.3 µg/L) for 4 and 12 days using a mesocosm system. PK activity was not affected by stressors. LDH, CS, IDH, ETS and G6PDH activities were temporally inhibited by stressors alone. CS, ETS and G6PDH activities remained inhibited by the combination of stressors after 12 days. Furthermore, all combinations between increasing temperature and exposure Cu were synergistic after prolonged exposure. Taken together, stressors applied alone led to temporary inhibitory effects on energy metabolism enzymes of the coral M. harttii, however, prolonged exposure reveals strong deleterious effects over the metabolism of corals due to the combination of stressors. The present study is the first one to give insights into the combined effects of increasing temperature and Cu exposure in the energy metabolism enzymes of a scleractinian coral. Findings suggest that moderate Cu contamination in future increasing temperature scenarios can be worrying for aerobic and oxidative metabolism of M. harttii.

The effect of dissolved nickel and copper on the adult coral Acropora muricata and its microbiome.

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.

Bleaching and necrosis of staghorn coral (Acropora formosa) in laboratory assays: Immediate impact of LDPE microplastics.

The impact of low-density polyethylene (LDPE) microplastics (<100 µm; P100-A P100-B, P100-C, 100-200 µm; P200, 200-500 µm; P500) on Acropora formosa was investigated. This study investigated the bleaching and necrosis extent of A. formosa caused by LDPE contamination via laboratory assay. The staghorn coral ingested the microplastics, resulting in bleaching and necrosis that concomitantly occurred with the release of zooxanthellae. P100-A experimentation was the worst case, showing bleaching by day 2 (10.8 ±â€¯2.2%) and continued bleaching to 93.6% ±â€¯2.0 by day 14 followed by 5.9 ±â€¯2.5% necrosis. The overall results confirmed that the LDPE concentration impacts coral health. We highlighted that microplastics have been ingested and partially egested. Their presence showed either a direct or indirect impact on coral polyps via direct interaction or through photosynthesis perturbation due to microplastics that cover the coral surface.

Sunscreen bans: Coral reefs and skin cancer.

WHAT IS KNOWN AND OBJECTIVE: Hawaii will ban two major ingredients of sunscreens. This article reviews the reasons and future directions. Hawaii recently enacted legislation that will ban the use of two major ingredients of the majority of commonly used sunscreens. The reason for the ban is the ingredients' putative deleterious impact on marine ecosystems, particularly coral reefs. But sunscreens also save lives by decreasing the risk of UV-induced skin cancers. We review both sides of the issue and potential implications for the healthcare system. COMMENT: Coral reefs consist of organisms in delicate equilibria that are susceptible to small changes in their surroundings. Recent natural and man-made disruptions, direct or indirect, such as changes in ocean temperature and chemistry, ingress of invasive species, pathogens, pollution and deleterious fishing practices, have been blamed for the poor health, or even the outright destruction, of some coral reefs. The most popular sunscreen products contain two ingredients-oxybenzone and octinoxate-that have also been implicated in coral toxicity and will be banned. This creates a healthcare dilemma: Will the protection of coral reefs result in an increase in human skin cancers? WHAT IS NEW AND CONCLUSION: Concentration estimates and mechanism studies support an association-direct or indirect (via promotion of viral infection)-of sunscreens with bleaching of coral reefs. A ban on the two most common sunscreen ingredients goes into effect in Hawaii on January 1, 2021. Proponents suggest that this is a trend, just the first of many such bans worldwide; opponents warn of a dire increase in human skin cancers. As a result, alternative sunscreen compounds are being sought.

Macro- and microplastics affect cold-water corals growth, feeding and behaviour.

Plastic contamination is now recognized as one of the most serious environmental issues for oceans. Both macro- and microplastic debris are accumulating in surface and deep waters. However, little is known about their impact on deep marine ecosystems and especially on the deep-sea reefs built by emblematic cold-water corals. The aim of this study was to investigate whether plastics affected the growth, feeding and behaviour of the main engineer species, Lophelia pertusa. Our experiments showed that both micro- and macroplastics significantly reduced skeletal growth rates. Macroplastics induced an increased polyp activity but decreased prey capture rates. They acted as physical barriers for food supply, likely affecting energy acquisition and allocation. Inversely, microplastics did not impact polyp behaviour or prey capture rates, but calcification was still reduced compared to control and in situ conditions. The exact causes are still unclear but they might involve possible physical damages or energy storage alteration. Considering the high local accumulation of macroplastics reported and the widespread distribution of microplastics in the world ocean, our results suggest that plastics may constitute a major threat for reef aggradation by inhibiting coral growth, and thus jeopardise the resilience of cold-water coral reefs and their associated biodiversity.

Occurrence and Composition of Microplastics in the Seabed Sediments of the Coral Communities in Proximity of a Metropolitan Area.

In marine environments, microplastics have become a focus in scientific research in the last decade due to the global threat this pollutant poses to the marine environment. Corals in Hong Kong are under threat due to the degradation of the marine environment caused by human activities. This study investigated the occurrence, abundance and composition of microplastic debris (0.3⁻5 mm) in seabed sediments adjacent to coral communities in Hong Kong. Twenty-four benthic sediment samples were collected from four study sites located along the northeastern and eastern shores of Hong Kong. Microplastic concentrations ranged from 169 ± 48 to 221 ± 45 items/kg, and the mean concentration of microplastics in the seabed sediments was 189 ± 50 items/kg, which was comparable to similar studies in other regions. Microplastics accounted for 95.4% of particles extracted from benthic sediment samples using 40× light microscopy. ATR-FTIR spectroscopy analysis showed that polyethylene (PE) and polyethylene terephthalate (PET) comprised the majority of polymer types, contributing 45.3% and 29.3%, respectively. The proportion of microplastics made from PE and PET in seabed sediments was significantly higher than that observed in local beach sediments. The proportion of microplastics made from PE and low-density polyethylene (LDPE) and polypropylene (PP) together in the seabed sediments was much higher than that of PET and polyvinyl chloride (PVC). The results have provided information with reference to environmental concentrations of microplastics for fringe reef habitat close to urban areas, which can be applied in studies concerning ecotoxicity of microplastics.

Gene expression profiling reveals deep-sea coral response to the Deepwater Horizon oil spill.

Deep-sea coral communities are key components of the Gulf of Mexico ecosystem and were adversely affected by the Deepwater Horizon (DWH) oil spill. Coral colonies exposed to oil and dispersant exhibited mortality, damage and physiological signatures of stress. Understanding how corals respond to oil and dispersant exposure at the molecular level is important to elucidate the sublethal effects of the DWH disaster and reveal broader patterns of coral stress responses. Gene expression profiles from RNAseq data were compared between corals at an impacted site and from a reference site. A total of 1,439 differentially expressed genes (≥twofold) were shared among impacted Paramuricea biscaya colonies. Genes involved in oxidative stress, immunity, wound repair, tissue regeneration and metabolism of xenobiotics were significantly differentially expressed in impacted corals. Enrichment among the overexpressed genes indicates the corals were enduring high metabolic demands associated with cellular stress responses and repair mechanisms. Underexpression of genes vital to toxin processing also suggests a diminished capacity to cope with environmental stressors. Our results provide evidence that deep-sea corals exhibited genome-wide cellular stress responses to oil and dispersant exposure and demonstrate the utility of next-generation sequencing for monitoring anthropogenic impacts in deep waters. These analyses will facilitate the development of diagnostic markers for oil and dispersant exposure in deep-sea invertebrates and inform future oil spill response efforts.

Enhancement of coral calcification via the interplay of nickel and urease.

Corals are the main reef builders through the formation of calcium carbonate skeletons. In recent decades, coral calcification has however been impacted by many global (climate change) and local stressors (such as destructive fishing practices and changes in water quality). In this particular context, it is crucial to identify and characterize the various factors that promote coral calcification. We thus performed the first investigation of the effect of nickel and urea enrichment on the calcification rates of three coral species. These two factors may indeed interact with calcification through the activity of urease, which catalyzes the hydrolysis of urea to produce inorganic carbon and ammonia that are involved in the calcification process. Experiments were performed with the asymbiotic coral Dendrophyllia arbuscula and, to further assess if urea and/or nickel has an indirect link with calcification through photosynthesis, results were compared with those obtained with two symbiotic corals, Acropora muricata and Pocillopora damicornis, for which we also measured photosynthetic rates. Ambient and enriched nickel (0.12 and 3.50 µg L-1) combined with ambient and enriched urea concentrations (0.26 and 5.52 µmol L-1) were tested during 4 weeks in aquaria. We demonstrate in the study that a nickel enrichment alone or combined with a urea enrichment strongly stimulated urea uptake rates of the three tested species. In addition, this enhancement of urea uptake and hydrolysis significantly increased the long-term calcification rates (i.e. growth) of the three coral species investigated, inducing a 1.49-fold to 1.64-fold increase, respectively for D. arbuscula and P. damicornis. Since calcification was greatly enhanced by nickel in the asymbiotic coral species - i.e. in absence of photosynthesis - we concluded that the effect of increased urease activity on calcification was mainly direct. According to our results, it can be assumed that corals in some fringing reefs, benefiting from seawater enriched in nickel may have advantages and might be able to use urea more effectively as a carbon and nitrogen source. It can also be suggested that urea, for which hotspots are regularly measured in reef waters may alleviate the negative consequences of thermal stress on corals.

Systemic response of the stony coral Pocillopora damicornis against acute cadmium stress.

Heavy metals have become one of the main pollutants in the marine environment and a major threat to the growth and reproduction of stony corals. In the present study, the density of symbiotic zooxanthellae, levels of crucial physiological activities and the transcriptome were investigated in the stony coral Pocillopora damicornis after the acute exposure to elevated cadmium concentration. The density of symbiotic zooxanthellae decreased significantly during 12-24h period, and reached lowest at 24h after acute cadmium stress. No significant changes were observed in the activity of glutathione S-transferase during the entire stress exposure. The activities of superoxide dismutase and catalase, and the concentration of glutathione decreased significantly, but the activation level of caspase3 increased significantly after cadmium exposure. Furthermore, transcriptome sequencing and bioinformatics analysis revealed 3538 significantly upregulated genes and 8048 significantly downregulated genes at 12h after the treatment. There were 12 overrepresented GO terms for significantly upregulated genes, mostly related to unfolded protein response, endoplasmic reticulum stress and apoptosis. In addition, a total of 32 GO terms were overrepresented for significantly downregulated genes, and mainly correlated with macromolecular metabolic processes. These results collectively suggest that acute cadmium stress could induce apoptosis by repressing the production of the antioxidants, elevating oxidative stress and activating the unfolded protein response. This cascade of reactions would result to the collapse of the coral-zooxanthella symbiosis and the expulsion of symbiotic zooxanthellae in the stony coral P. damicornis, ultimately leading to coral bleaching.

Sediment-associated polycyclic aromatic hydrocarbons and potential eco-hazards in Chabahar Bay, Iran.

The surface sediments (0-4cm, n=6) from Chabahar Bay were analyzed to assess the concentrations, composition, and potential eco-hazards of associated PAHs. The range of ∑16 PAHs' concentration was 25.75-312.38ngg-1 dw, with mean and median levels of 126.7 and 55.12ngg-1 dw, respectively. The bay was classified as a region with low to moderate PAH pollution. The sources of PAHs varied, and 2-3-ring compounds were dominant (37-90%). There was no significant correlation between TOC/grain size and levels of PAHs. Total carcinogenic PAHs ranged from 0.21 to 79.68ngg-1 dw, and benzo(a)pyrene was the main constituent of calculated toxic equivalencies. The bay sediments were rarely hazardous and could not address narcotic hazards for the benthic community. Biota-sediment accumulation was not predicted for the examined coral Acropora valida. In equilibrium conditions, release of ∑16PAHs from the bay sediments was estimated to be 0.536µgL-1 at its maximum.

The characterization of iron (III) in seawater and related toxicity to early life stages of scleractinian corals.

Currently toxicity data for iron (Fe) in seawater are limited; furthermore, these data are of poor quality as a result of the importance of Fe solubility in test solutions being overlooked. The present study characterized the solubility and lability of Fe(III) in seawater and then examined the effects of Fe(III) on the fertilization success and larval survival of the tropical marine scleractinian corals Acropora spathulata and Platygyra daedalea. We present the first assessment of the effects of Fe on the early life stages of scleractinian corals. Concentrations of both soluble and labile forms of Fe were very low, with dissolved Fe concentrations ≤0.195 mg/L in bioassay test solutions and chemical determinations revealing labile Fe concentrations ≤1.21 mg/L. For fertilization experiments, the median effect concentration (EC50) value for total Fe was 25 mg/L for the most sensitive species, P. daedalea, whereas the EC50 values for A. spathulata ranged between 40 and 66 mg/L. The median lethal concentration value for P. daedalea larval survival was 47 mg/L Fe after 72-h exposure. We provide Fe toxicity data for tropical marine keystone species that could be used to help generate more reliable guideline values for Fe in marine waters. Environ Toxicol Chem 2018;37:1104-1114. © 2017 SETAC.