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Coral bleaching is occurring more frequently as the climate changes, with multiple mass mortality events recently recorded on the Great Barrier Reef. Thermal stress coupled with high irradiance have previously been shown to be primary causes for coral bleaching. Therefore, a reduction in either of these pressures could reduce coral stress and eventual bleaching. Herein, we report the early development of a novel technology capable of reducing the amount of light entering a water body by ~20% in open ocean conditions. This mono-particle "sun shield" consists of an ultra-thin monolayer material and reflective calcium carbonate particles. The monolayer enables spreading of the particles into a thin film across the water surface, with only small amounts of material needed: 7.1 g/m2. A numerical modelling case study of residence times and the build-up of reactive oxygen stress in corals showed that the successful application of a stable film over the Lizard Island reef flat could reduce the reactive oxygen stress to below bleaching levels across approximately 1.5 km2 of reef area. With further development, mono-particle films such as this have the potential to be deployed over at-risk coral reefs at relatively small scales during predicted heatwave conditions, potentially reducing the severity of bleaching on coral reefs. [ABSTRACT FROM AUTHOR]

A range of new statistical approaches is being developed and/or adopted in ecotoxicology that, when combined, can greatly improve the estimation of no‐effect toxicity values from concentration–response (CR) experimental data. In particular, we compare the existing no‐effect‐concentration (NEC) threshold‐based toxicity metric with an alternative no‐significant‐effect‐concentration (NSEC) metric suitable for when CR data do not show evidence of a threshold effect. Using a model‐averaging approach, these metrics can be combined to yield estimates of N(S)EC and of their uncertainty within a single analysis framework. The outcome is a framework for CR analysis that is robust to uncertainty in the model formulation, and for which resulting estimates can be confidently integrated into risk assessment frameworks, such as the species sensitivity distribution (SSD). Integr Environ Assess Manag 2024;20:279–293. © 2023 Commonwealth of Australia and The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Key Points: Estimating concentrations of "no‐effect" of contaminants is critical to effective environmental risk assessment and management.Concentration–response (CR) data can take many forms and do not always exhibit the clear threshold responses required for no‐effect‐concentration (NEC) threshold‐based toxicity models to be validly applied.We compare the existing NEC threshold‐based toxicity metric with an alternative no‐significant‐effect‐concentration (NSEC) metric suitable for when CR data do not show evidence of a threshold effect.We demonstrate how, embedded in a model‐averaging approach, the NEC and NSEC can be combined in a single analysis to yield estimates of N(S)ECs and of their uncertainty. [ABSTRACT FROM AUTHOR]

Tropical marine ecosystems, such as coral reefs, face several threats to their health and resilience, including poor water quality. Previous studies on the risks posed by pesticides have focused on five priority herbicides; however, as the number of pesticides applied in coastal agriculture increases, a suite of 'alternative' pesticides is being detected in tropical nearshore waters. To improve our understanding of the risks posed by alternative pesticides to tropical marine organisms, the effects of three insecticides (diazinon, fipronil, imidacloprid) and two fungicides (chlorothalonil, propiconazole) were tested on larval metamorphosis of the coral Acropora tenuis. A. tenuis larvae were affected by all five pesticides and the reference toxicant copper. The no effect concentration (NEC) and the 10% and 50% effect concentrations (EC10 and EC50, respectively) for larval metamorphosis were estimated from concentration-response curves after 48 h exposure. The NEC, EC10 and EC50 (in µg L-1), respectively, of each pesticide were as follows: chlorothalonil (2.4, 2.8, 6.0); fipronil (12.3, 13.9, 29.1); diazinon (38.0, 40.8, 54.7); imidacloprid (263, 273, 347); and propiconazole (269, 330, 1008). These toxicity thresholds are higher than reported concentrations in monitoring programs; however, these data will contribute to improving water quality guideline values, which inform the total risk assessments posed by complex contaminant mixtures to which these pesticides contribute. [ABSTRACT FROM AUTHOR]

Crustose coralline algae ( CCA) are a critical component of coral reefs as they accrete carbonate for reef structure and act as settlement substrata for many invertebrates including corals. CCA host a diversity of microorganisms that can also play a role in coral settlement and metamorphosis processes. Although the sensitivity of CCA to ocean acidification ( OA) is well established, the response of their associated microbial communities to reduced pH and increased CO2 was previously not known. Here we investigate the sensitivity of CCA-associated microbial biofilms to OA and determine whether or not OA adversely affects the ability of CCA to induce coral larval metamorphosis. We experimentally exposed the CCA Hydrolithon onkodes to four pH/ p CO2 conditions consistent with current IPCC predictions for the next few centuries ( pH: 8.1, 7.9, 7.7, 7.5, p CO2: 464, 822, 1187, 1638 μatm). Settlement and metamorphosis of coral larvae was reduced on CCA pre-exposed to pH 7.7 ( p CO2 = 1187 μatm) and below over a 6-week period. Additional experiments demonstrated that low pH treatments did not directly affect the ability of larvae to settle, but instead most likely altered the biochemistry of the CCA or its microbial associates. Detailed microbial community analysis of the CCA revealed diverse bacterial assemblages that altered significantly between pH 8.1 ( p CO2 = 464 μatm) and pH 7.9 ( p CO2 = 822 μatm) with this trend continuing at lower pH/higher p CO2 treatments. The shift in microbial community composition primarily comprised changes in the abundance of the dominant microbes between the different pH treatments and the appearance of new (but rare) microbes at pH 7.5. Microbial shifts and the concomitant reduced ability of CCA to induce coral settlement under OA conditions projected to occur by 2100 is a significant concern for the development, maintenance and recovery of reefs globally. [ABSTRACT FROM AUTHOR]

Tooth hypersensitivity can occur when gum recession causes exposure of dentin. Tiny tubules, which permeate dentin, provide open passageways from the mouth to the intradental nerve in the pulpal cavity. Under such circumstances, stimuli in the mouth can cause pressure on the intradental nerve, leading to pain. Sealing the outside of the tubules with an impermeable substance can effectively treat hypersensitivity. One such clinically proven composition is a professionally applied tooth desensitizer, which has been shown to initially produce a layer of amorphous calcium phosphate (ACP) on the surface of dentin. Under the influence of fluoride, ACP reforms as hydroxyapatite (HAP), which has essentially the same composition as tooth mineral. Three fluoride toothpastes that deliver calcium and phosphate salts to the teeth also have been demonstrated in clinical trials to relieve hypersensitivity. This study compared the mechanism of action of these toothpastes to that of the professional desensitizer. A single application of the professional desensitizer or multiple applications of any of the three toothpastes was shown to reduce dentin permeability. A conventional fluoride toothpaste also was found to inhibit fluid flow through the dentin but to a lesser degree than the other toothpastes. The desensitizer and the three toothpastes were found to occlude the dentinal tubules with a layer of calcium phosphate that had a calcium-to-phosphate ratio consistent with the formation of ACP or HAP. The morphology of the coherent mineral layer formed by Arm & Hammer Enamel Care Sensitive was similar, especially to that produced by the desensitizer. In contrast, the conventional toothpaste left localized areas of surface residue composed of silica particles. The mechanism of action of the three toothpastes that deliver calcium and phosphate salts is the same as that of the professional desensitizer. [ABSTRACT FROM AUTHOR]