Background: Tropical coral reefs have been recognized for their significant ecological and economical value. However, increasing anthropogenic disturbances have led to progressively declining coral reef ecosystems on a global scale. More recently, several studies implicated UV filters used in sunscreen products to negatively affect corals and possibly contribute to regional trends in coral decline. Following a public debate, bans were implemented on several organic UV filters and sunscreen products in different locations including Hawaii, the U.S. Virgin Islands and Palau. This included banning the widely used oxybenzone and octinoxate, while promoting the use of inorganic filters such as zinc oxide even although their toxicity towards aquatic organisms had been documented previously. The bans of organic UV filters were based on preliminary scientific studies that showed several weaknesses as there is to this point no standardized testing scheme for scleractinian corals. Despite the lack of sound scientific proof, the latter controversial bans have already resulted in the emergence of a new sunscreen market for products claimed to be ‘reef safe’ (or similar). Thus, a market analysis of ‘reef safe’ sunscreen products was conducted to assess relevant environmental safety aspects of approved UV filters, especially for coral reefs. Further, a scientifically sound decision-making process in a regulatory context is proposed. Results: Our market analysis revealed that about 80% of surveyed sunscreens contained inorganic UV filters and that there is a variety of unregulated claims being used in the marketing of ‘reef safe’ products with ‘reef friendly’ being the most frequently used term. Predominantly, four organic UV filters are used in ‘reef safe’ sunscreens in the absence of the banned filters oxybenzone and octinoxate. Analysis of safe threshold concentrations for marine water retrieved from existing REACH registration dossiers could currently also safeguard corals. Conclusion: There is a substantial discrepancy of treatments of organic versus inorganic UV filters in politics as well as in the ‘reef safe’ sunscreen market, which to this point is not scientifically justified. Thus, a risk-based approach with equal consideration of organic and inorganic UV filters is recommended for future regulatory measures as well as a clear definition and regulation of the ‘reef safe’ terminology.

The pollution of the marine environment with microplastics is pervasive. However, microplastic concentrations in the seawater are lower than the number of particles entering the oceans, suggesting that plastic particles accumulate in environmental sinks. Yet, the exact long‐term sinks related to the “missing plastic” phenomenon are barely explored. Sediments in nearshore biogenic habitats are known to trap large amounts of microplastics, but also the three‐dimensional structures of coral reefs might serve as unique, living long‐term sinks. The main framework builders, reef‐building corals, have been shown to ingest and overgrow microplastics, potentially leading to a deposition of particles in reef structures. However, little is known about the number of deposited particles and the underlying processes determining the permanent deposition in the coral skeletons. To test whether corals may act as living long‐term sink for microplastic, we exposed four reef‐building coral species to polyethylene microplastics (200 particles L⁻¹) in an 18‐month laboratory experiment. We found microplastics in all treatment specimens, with low numbers of particles trapped in the coral tissue (up to 2 particles per cm²) and much higher numbers in the skeleton (up to 84 particles per cm³). The numbers of particles accumulated in the coral skeletons were mainly related to coral growth (i.e., skeletal growth in volume), suggesting that deposition is a regularly occurring stochastic process. We estimate that reef‐building corals may remove 0.09%–2.82% of the bioavailable microplastics from tropical shallow‐reef waters per year. Our study shows for the first time that microplastic particles accumulate permanently in a biological sink, helping to explain the “missing plastic” phenomenon. This highlights the importance of coral reefs for the ecological balance of the oceans and reinforces the need to protect them, not only to mitigate the effects of climate change but also to preserve their ecosystem services as long‐term sink for microplastic.

Coral reefs are highly endangered ecosystems. The identification and quantification of potential stress factors are essential to protect them. UV filters from sunscreens that are introduced to coral reef areas are considered as one of these stressors and their impact on corals needs to be further investigated. Even though UV filters are functionally similar, their structural features are very diverse. Their impact on limnic organisms have also been shown to be highly variable ranging from no or low to high toxicity. It is therefore to be expected that their effect on corals also differs significantly and that each compound has to be evaluated individually. The demand for conclusive benchmarks and guidelines from policy makers and the public over the past years shows the necessity for an objective literature review on the effects of various UV filters on scleractinian corals. Here, we review the present literature, summarize the data on the different UV filters and discuss the different approaches, advantages and limitations of the studies. However, the methods used in the latter studies vary greatly. They differ in many aspects such as species and life stage used, field and laboratory approaches, with exposure times ranging from hours to weeks. Some studies include analytics and measure the actual test concentration, others only provide nominal concentrations. The lack of standardized methods renders comparisons between studies futile. Additionally, most UV filters have only been investigated in a single or a few studies of different quality. Reliable thresholds are therefore impossible to draw on the basis of currently available studies. Nevertheless, certain UV filters repeatedly showed comparable toxicity in both freshwater and marine species tested. Yet, existing differences in results from coral tests emphasize the need for a standardized testing method comparable to those established for other aquatic organisms in order to allow for a more conclusive assessment. In this review, we describe what a scientifically sound testing proposal should include in order to obtain reliable and reproducible data, which ultimately should result in an internationally organized standardized ring test trial. Such standardized toxicity tests would enable validation of coral toxicity data related to UV filters, but also testing of other types of compounds that are known to be introduced and effect coral reefs, thus helping to identify significant stressors and enabling objective policy decisions.

Shark bites are of high public concern globally. Information on shark occurrence and behaviour, and of the effects of human behaviours, can help understand the drivers of shark‐human interactions. In Australia, a number of shark bite clusters occurred over the last decade. One of these took place in Cid Harbour the Whitsundays, Queensland, a region for which little was known about the shark community. Here, we describe and evaluate the research in response to that shark bite cluster. Fishing methods, acoustic and satellite tracking, and baited remote underwater video cameras (BRUVs) were used to identify the shark species using Cid Harbour, estimate relative abundance, and describe habitat use and residency. Side‐scan sonar and BRUVs were also used to assess prey availability. Recreational users were surveyed to understand human behaviour and their awareness and perceptions of ‘Shark Smart’ behaviours. This allowed shark occurrence and behaviour to be interpreted in the context of human behaviours in the Harbour. Eleven shark species were identified. Relative abundance was not unusually high, and residency in Cid Harbour was typically low. For example, 79% of acoustically tagged sharks visited the harbour on <10% days at liberty. Shark prey was available year‐round. Notably, anchored boats regularly conduct activities that can attract sharks (dumping food scraps, provisioning and cleaning fish). Alone, the methods used in this study had variable success, but combined they provided a large amount of complementary information. Including a social science component in the research response to the shark bite incidents allowed for a more holistic understanding of the Cid Harbour bite incidents. This study did not identify anything unusual about the shark community that could have contributed to the Cid Harbour shark bite cluster. However, the three incidents involved people bitten almost instantly after entering the water, which is unusual and suggests that feeding/attracting sharks to boats could have been a contributor and also that any species capable of biting humans could have been responsible. The eradication of activities that attract sharks to areas where people enter the water may reduce shark bite risk. Read the free Plain Language Summary for this article on the Journal blog.

Coral reefs have been declining globally at a historically unprecedented rate. Ultraviolet (UV) filters used in sunscreens may contribute to this decline at local scales, which has already led to bans on various organic UV filters in some regions. However, the underlying studies for these bans demonstrated significant flaws in the experimental design due to a lack of validated and standardized testing methods for corals. This study aimed to investigate options for the development of a standard acute toxicity test for the larval stage of scleractinian corals. Planula larvae of two brooding (Leptastrea purpurea and Tubastraea faulkneri) and two spawning (Acropora digitifera and A. millepora) species were exposed to the organic UV filter benzophenone-3 (BP3) for 48 h under static conditions. We observed interspecific variations in toxicity, with A. digitifera being the most sensitive (LC₅₀ = 0.75 µg L⁻¹) and T. faulkneri the least sensitive (LC₅₀ = 2951.24 µg L⁻¹) species. Inhibition of settlement was found to be a useful endpoint leading to an EC₅₀ of 1.84 µg L⁻¹ in L. purpurea larvae. Although the analytical challenges of measuring lipophilic substances in small volume test setups remain, the here applied test design and selected endpoints are suitable for further validation and subsequent standardization.

Information on how the trophic ecology of predators shapes their movement patterns and space-use is fundamental to understanding ecological processes across organisational levels. Despite this, studies combining spatial and trophic ecology to determine how prey preference and/or resource availability shape space use are lacking in marine predators as these can occur at low density and are often difficult to track over extended periods. Furthermore, many exhibit behavioural variability within species and among closely related, sympatric species adding further complexity. We applied a context-focused, multi-method approach to the understudied great hammerhead shark (Sphyrna mokarran) to test if movement and home ranges relate to prey preference and availability. Movement data from satellite and acoustic telemetry in Queensland, Australia, were combined with stable-isotope analysis, drone surveys, and videos of hunting behaviour. Limited dispersal, and small home ranges in S. mokarran were linked to trophic specialisation on stingray prey. Drone surveys and videos showed predation events on stingrays and demonstrated high, year-round availability of this prey in shallow, inshore habitats, which may allow the majority of S. mokarran to remain resident. This affinity for inshore habitats suggests that critical life-history requirements are performed over local or regional scales, although some larger movements were evident. These results were interpreted in comparison to the well-studied bull shark (Carcharhinus leucas), which showed reliance on pelagic food webs. Carcharhinus leucas had high individual variability in movement, with both large-scale migrations and residency. This could indicate that only some individuals are locally sustained on dynamic, pelagic food webs, while others undergo large-scale excursions over distant habitats. The specialised foraging of S. mokarran indicates they play an apex predator role in shallow, inshore habitats, potentially shaping space-use, and foraging behaviour of batoids. As inshore habitats are disproportionately affected by anthropogenic stressors, S. mokarran’s trophic specialisation and limited demographic connectivity may make the species particularly vulnerable to anthropogenic threats.