An assessment of people living by coral reefs over space and time

Scaling-up coral reef carbonate production: Sea-urchin bioerosion suppresses reef growth in Hawai'i

Coral reefs provide essential social, economic, and ecological services for millions of people worldwide. Yet, climate change and local anthropogenic stressors are damaging reefs globally, compromising their framework-building capacity and associated functionality. A reef carbonate budget provides a quantitative measure of growth and functional status, but utilization of remote sensing to scale-up such a metric remains limited. This study used census-based field surveys across depths in Hōnaunau Bay, Hawai'i to examine rates of carbonate production, and scaled-up estimates across the bay with high-resolution benthic-cover data derived from airborne imaging spectroscopy. Average net carbonate production was ~0.5 kg CaCO3 m-2 y-1 across the 2-17 m depth gradient, ranging from -2.1 to 2.4 kg CaCO3 m-2 y-1 at 3 and 6 m, respectively. The scaling model with the lowest root mean square error was achieved using a 2-m resolution map of live coral cover. Sea-urchin densities averaged 51 individuals m-2, which were among the highest recorded densities on coral reefs globally. The subsequent high bioerosion from sea urchins suppressed estimated reef-growth potential, particularly in the shallow reef <6 m. Field estimates of net carbonate production translate to vertical reef accretion of ~0.5 mm y-1 across depths, indicating the reef in its present form is not keeping pace with the current rate of sea-level rise (3.55 mm y-1) in west Hawai'i. These results suggest a need for improved fisheries management in Hōnaunau Bay to enhance carnivorous-fish abundances, thereby helping to reduce sea-urchin densities and improve reef-growth capacity. Critically, an estimated threshold of ~26% live coral cover is currently needed to maintain positive net production across depths. This study demonstrates the utility of monitoring carbonate production by integrating field measurements and airborne imaging spectroscopy, and highlights the need for management decisions in west Hawai'i that enhance resilient carbonate budgets of coral reefs.

Simulation-based inference advances water quality mapping in shallow coral reef environments

Human activities are altering coral reef ecosystems worldwide. Optical remote sensing via satellites and drones can offer novel insights into where and how coral reefs are changing. However, interpretation of the observed optical signal (remote-sensing reflectance) is an ill-posed inverse problem, as there may be multiple different combinations of water constituents, depth and benthic reflectance that result in a similar optical signal. Here, we apply a new approach, simulation-based inference, for addressing the inverse problem in marine remote sensing. The simulation-based inference algorithm combines physics-based analytical modelling with approximate Bayesian inference and machine learning. The input to the algorithm is remote-sensing reflectance, and the output is the likely range (posterior probability density) of phytoplankton and suspended minerals concentrations, coloured dissolved organic matter absorption, wind speed and depth. We compare inference models trained with simulated hyperspectral or multispectral reflectance spectra characterized by different signal-to-noise ratios. We apply the inference model to in situ radiometric data (n = 4) and multispectral drone imagery collected on the Tetiaroa atoll (South Pacific). We show that water constituent concentrations can be estimated from hyperspectral and multispectral remote-sensing reflectance in optically shallow environments, assuming a single benthic cover. Future developments should consider spectral mixing of multiple benthic cover types.

Biomimetic chemical microhabitats enhance coral settlement

Anthropogenic stressors pose substantial threats to the existence of coral reefs. Achieving successful coral recruitment stands as a bottleneck in reef restoration and hybrid reef engineering efforts. Here, we enhance coral settlement through the development of biomimetic microhabitats that replicate the chemical landscape of healthy reefs. We engineered a soft biomaterial, SNAP-X, comprising silica nanoparticles (NPs), biopolymers, and algal exometabolites, to enrich reef microhabitats with bioactive molecules from crustose coralline algae (CCA). Coral settlement was enhanced over 20-fold using SNAP-X-coated substrates compared with uncoated controls. SNAP-X is designed to release chemical signals slowly (>1 month) under natural seawater conditions, and can be rapidly applied to natural reef substrates via photopolymerization, facilitating the light-assisted 3D printing of microengineered habitats. We anticipate that these biomimetic chemical microhabitats will be widely used to augment coral settlement on degraded reefs and to support ecosystem processes on hybrid reefs.

Restoration cannot be scaled up globally to save reefs from loss and degradation

Coral restoration is gaining popularity as part of a continuum of approaches addressing the widespread, recurring mass mortality events of corals that-together with elevated and chronic mortality, slower growth and recruitment failure-threaten the persistence of coral reefs worldwide. However, the monetary costs associated with broad-scale coral restoration are massive, making widespread implementation challenging, especially with the lack of coordinated and ecologically informed planning. By combining a comprehensive dataset documenting the success of coral restoration with current and forecasted environmental, ecological and climate data, we highlight how such a coordinated and ecologically informed approach is not forthcoming, despite the extent of previous and ongoing efforts. We show that: (1) restoration sites tend to be disproportionally close to human settlements and therefore more vulnerable to local anthropogenic impacts; (2) the immediate outcomes of restoration do not appear to be influenced by relevant ecological and environmental predictors such as cumulative impact; and (3) most restored localities have a high and severe bleaching risk by the middle of this century, with more than half of recently restored sites already affected. Our findings highlight the need for the coral reef community to reinforce joint development of restoration guidelines that go beyond local objectives, with attention to ocean warming trends and their long-term impacts on coral resilience and restoration success.

Sea-weeding enhances early coral survival on seeding devices, but benefits of seeding diminish after one year

Borrowing from principles of aerial seeding in terrestrial reforestation, coral seeding utilises "devices" designed to increase coral spat survival. However, device-assisted coral survival has not been compared to natural survivorship, nor have devices been trialled in environments with strong competitors such as macroalgae. Herein, we deployed seeded devices alongside terracotta tiles, a proxy for natural coral recruitment dynamics. Tiles and devices were deployed to plots examining ongoing macroalgae removal ("sea-weeding"), and survival was monitored over two years. First-year coral survival was enhanced on devices compared to natural survival, and devices conferred the greatest survival benefit when deployed in areas where "sea-weeding" was undertaken. However, over the second year, the benefits of sea-weeding for device-assisted survival were lost, with no significant difference in survival on devices in control versus weeded plots. On average, devices retained 1.3 surviving colonies at two years, which was lower than naturally-occurring juvenile density in removal plots, but higher than control plots. Several factors influenced survival, including the starting spat density, orientation of deployment surface, and site. After two years, 50 % of devices yielded one live coral, but site-based survival varied between 37 % and 93 %. The estimated cost per surviving coral varied when accounting for site-based survival (high survival: $334 coral-1; low survival: $577 coral-1), which could be reduced via future efficiencies. The results of this study inform the potential outcomes of coral seeding on macroalgae dominated reefs, and highlight that assessing survival up to one year is not sufficient to measure long-term restoration goals.

High-resolution temporal assessment of physicochemical variability and water quality in tropical semi-enclosed bays and coral reefs

Tropical coastlines featuring mangrove, seagrass, and coral habitats are of immense ecological and socio-economic importance, supporting biodiversity, carbon storage, coastal protection, fisheries, and tourism. However, climate change, coastal development, and low water quality increasingly threaten these interconnected coastal ecosystems, particularly in semi-enclosed bays where the impacts of these stressors are often amplified. Yet, physicochemical conditions are rarely assessed at sufficient temporal resolution (i.e., diel and seasonal variation) and time-integrated pollution monitoring is rarely performed. Here, we used a multi-disciplinary approach to assess >20 abiotic parameters characterizing two mangrove- and seagrass-dominated inland bays and two nearby coral reefs in Curaçao (southern Caribbean) during the cool, dry season and warm, wet season. This was combined with time-integrated pollution monitoring using bioindicators to assess nutrients and trace metal pollution (inland bays only), and passive samplers and bioassays to assess organic chemical pollution (all four sites) during the wet season. This approach revealed a previously undocumented extent of strong diel and seasonal environmental variability in Curaçao's inland bays, with temperature, pH, and dissolved oxygen frequently reaching values predicted under moderate-to-severe future climate scenarios as outlined by the IPCC (2021). In addition, the inland bays had greater nutrient concentrations (especially ammonium) and potential ecotoxicological risks than the nearby reefs during the wet season due to run-off and anthropogenic activities. These findings emphasize the importance of high-resolution monitoring to understand risks across appropriate temporal scales and establish an environmental baseline against which future monitoring can be benchmarked. Moreover, our study provides a robust water quality assessment framework that can be used by natural resource managers to monitor reef-associated habitats and conserve their high ecological and socio-economic value. Overall, our work highlights the urgent need to improve monitoring, water quality, and protection of these valuable reef-associated habitats.

Rapid Evolution in Action: Environmental Filtering Supports Coral Adaptation to a Hot, Acidic, and Deoxygenated Extreme Habitat

The semienclosed Bouraké lagoon in New Caledonia is a natural system that enables observation of evolution in action with respect to stress tolerance in marine organisms, a topic directly relevant to understanding the consequences of global climate change. Corals inhabiting the Bouraké lagoon endure extreme conditions of elevated temperature (> 33°C), acidification (7.2 pH units), and deoxygenation (2.28 mg O2 L-1), which fluctuate with the tide due to the lagoon's geomorphology. To investigate the underlying bases of the apparent stress tolerance of these corals, we combined whole genome resequencing of the coral host and ITS2 metabarcoding of the photosymbionts from 90 Acropora tenuis colonies from three localities along the steep environmental gradient from Bouraké to two nearby control reefs. Our results highlight the importance of coral flexibility to associate with different photosymbionts in facilitating stress tolerance of the holobiont; but, perhaps more significantly, strong selective effects were detected at specific loci in the host genome. Fifty-seven genes contained SNPs highly associated with the extreme environment of Bouraké and were enriched in functions related to sphingolipid metabolism. Within these genes, the conserved sensor of noxious stimuli TRPA1 and the ABCC4 transporter stood out due to the high number of environmentally selected SNPs that they contained. Protein 3D structure predictions suggest that a single-point mutation causes the rotation of the main regulatory domain of TRPA1, which may be behind this case of natural selection through environmental filtering. While the corals of the Bouraké lagoon provide a striking example of rapid adaptation to extreme conditions, overall, our results highlight the need to preserve the current standing genetic variation of coral populations to safeguard their adaptive potential to ongoing rapid environmental change.

Hybrid coral reef restoration can be a cost-effective nature-based solution to provide protection to vulnerable coastal populations

Coral reefs can mitigate flood damages by providing protection to tropical coastal communities whose populations are dense, growing fast, and have predominantly lower-middle income. This study provides the first fine-scale, regionally modeled valuations of how flood risk reductions associated with hybrid coral reef restoration could benefit people, property, and economic activity along Florida and Puerto Rico's 1005 kilometers of reef-lined coasts. Restoration of up to 20% of the regions' coral reefs could provide flood reduction benefits greater than costs. Reef habitats with the greatest benefits are shallow, nearshore, and fronting low-lying, vulnerable communities, which are often where reef impacts and loss are the greatest. Minorities, children, the elderly, and those below the poverty line could receive more than double the hazard risk reduction benefits of the overall population, demonstrating that reef restoration as a nature-based solution can have positive returns on investment economically and socially by providing protection to the most vulnerable people.

Reef visitors' observation of assisted coral recovery devices in situ reduces concern about their use

Assisted coral recovery (ACR) initiatives are establishing rapidly in coral reefs worldwide, using a variety of devices and techniques. In the Great Barrier Reef (GBR, the Reef), site-scale ACR field trials are occurring at multiple sites in the Cairns-Port Douglas region through Reef stewardship activities involving GBR tourism operators, Traditional Owners, and not-for-profit organisations. It is hypothesised that these field trials and the presence of ACR devices at reef tourism sites do not negatively affect visitor experiences, and when accompanied by appropriate educational information, can potentially help to raise awareness of Reef stewardship and conservation efforts. We tested these hypotheses using a survey of 708 Reef visitors on five tourism vessels, 346 of whom reported observing ACR devices in situ during their coral reef experience. Ordinal regression tests of survey responses found no statistical relationship between respondents' observation of ACR devices and (i) their overall Reef trip satisfaction, (ii) the perceived aesthetic beauty of the site(s) they visited, and (iii) their concern about the future health of the GBR. However, Reef visitors who observed ACR devices showed significantly lower levels of concern about the use of these devices on the Reef. The perceived quality of educational information presented to respondents was among the significant factors associated with their reef trip satisfaction and perceived beauty of reef sites. Our findings have implications for ACR practitioners and proponents who are concerned about public visibility, perceptions, and support for ACR initiatives, as the scale of such initiatives is expected to increase.

Coral reef protection is fundamental to human rights

The intensifying loss of coral reefs from global climate change and local stressors has seen international commitments targeted at conservation and repair, for example the Kunming-Montreal Global Biodiversity Framework. Fulfilling these targets requires decisions to be made on where, when, and how to act, ultimately dictating where limited resources will be deployed. Every choice on action or inaction toward our ocean has direct and indivisible consequences not only for the health of marine ecosystems but also for the health of humans, particularly those who directly depend on marine habitats, both culturally and economically. The well-being of the environment, humans, and animals is interlinked, co-dependent, and even co-produced, as has already been acknowledged by One Health approaches, which endorse a cross- and trans-disciplinary view to health. Coral reefs epitomie how tightly intertwined ecosystem health and the fate of the human and nonhuman communities that depend on them are. A field that thus far remains poorly considered is a human rights-based approach to coral reef protection. A human rights-based approach implements human rights obligations, including the recently affirmed right to a clean, healthy, and sustainable environment, while embedding principles of accountability, nondiscrimination, participation, and empowerment for local and Indigenous communities that ensure effectiveness and meaningful stakeholder engagement. Tying the protection of coral reef ecosystems to human rights emphasises the importance of healthy ecosystems to human well-being and thus the inevitable connection between nonhuman and human life. The general failure to consider coral reef protection through a human rights-based approach is a missed opportunity to expedite reef protection while simultaneously advancing climate justice for both humans and nonhumans.

Habitat quality effects on the abundance of a coral-dwelling fish across spatial scales

Microhabitat associated fishes are expected to be negatively affected by coral reef degradation, given that many species are coral dwellers. However, the factors underlying this negative impact and the spatial scale(s) at which it occurs are poorly understood. We explored how habitat quality metrics and host preferences influence fish abundance across multiple spatial scales, using the functionally important cleaner fish Elacatinus evelynae as a study species. We surveyed fish at 10 sites in Curaçao that varied in coral cover and health. At the microhabitat scale, we found that E. evelynae group size increases on large, healthy corals and on some coral host species, namely Montastraea cavernosa. We also found that, although E. evelynae can occupy at least 10 coral host species, it selectively inhabits just three corals: M. cavernosa, Colpophyllia natans, and Diploria labrynthiformis. Scaling up to explore goby abundance along 30-m transects, we did not find a clear relationship between live coral cover and goby abundance. However, goby abundance was substantially higher at one location with elevated coral cover and a high relative abundance of E. evelynae host species. Collectively, these results confirm that E. evelynae abundance is impacted by reef health. They also indicate that the species' long-term persistence may depend on both the maintenance of healthy coral hosts and the gobies' plasticity in host preferences on changing reefscapes. Cryptobenthic fishes such as E. evelynae play a vital role in the ecosystem and understanding drivers of their abundance is important as reefs face increased degradation.

Low human interest for the most at-risk reef fishes worldwide

Human interest in biodiversity is essential for effective conservation action but remains poorly quantified at large scales. Here, we investigated human interest for 2408 marine reef fishes using data obtained from online public databases and social media, summarized in two synthetic dimensions, research effort and public attention. Both dimensions are mainly related to geographic range size. Research effort is also linked to fishery importance, while public attention is more related to fish aesthetic value and aquarium trade importance. We also found a strong phylogenetic bias, with certain fish families receiving disproportional research effort and public attention. Most concerningly, species at the highest risk of extinction and those most vulnerable to future climate change tend to receive less research effort and public attention. Our results provide a lens through which examining the societal attention that species garner, with the ultimate goals to improve conservation strategies, research programs, and communication plans.

Quantifying energy and nutrient fluxes in coral reef food webs

The movement of energy and nutrients through ecological communities represents the biological 'pulse' underpinning ecosystem functioning and services. However, energy and nutrient fluxes are inherently difficult to observe, particularly in high-diversity systems such as coral reefs. We review advances in the quantification of fluxes in coral reef fishes, focusing on four key frameworks: demographic modelling, bioenergetics, micronutrients, and compound-specific stable isotope analysis (CSIA). Each framework can be integrated with underwater surveys, enabling researchers to scale organismal processes to ecosystem properties. This has revealed how small fish support biomass turnover, pelagic subsidies sustain fisheries, and fisheries benefit human health. Combining frameworks, closing data gaps, and expansion to other aquatic ecosystems can advance understanding of how fishes contribute to ecosystem functions and services.

Tropical fishery nutrient production depends on biomass-based management

The need to enhance nutrient production from tropical ecosystems to feed the poor could potentially create a new framework for fisheries science and management. Early recommendations have included targeting small fishes and increasing the species richness of fish catches, which could represent a departure from more traditional approaches such as biomass-based management. To test these recommendations, we compared the outcomes of biomass-based management with hypothesized factors influencing nutrient density in nearshore artisanal fish catches in the Western Indian Ocean. We found that enhancing nutrient production depends primarily on achieving biomass-based targets. Catches dominated by low- and mid-trophic level species with smaller body sizes and faster turnover were associated with modest increases in nutrient densities, but the variability in nutrient density was small relative to human nutritional requirements. Therefore, tropical fishery management should focus on restoring biomass to achieve maximum yields and sustainability, particularly for herbivorous fishes.

Coral reefs in transition: Temporal photoquadrat analyses and validation of underwater hyperspectral imaging for resource-efficient monitoring in Guam

The island of Guam in the west Pacific has seen a significant decrease in coral cover since 2013. Lafac Bay, a marine protected area in northeast Guam, served as a reference site for benthic communities typical of forereefs on the windward side of the island. The staghorn coral Acropora abrotanoides is a dominant and characteristic ecosystem engineer of forereef communities on exposed shorelines. Photoquadrat surveys were conducted in 2015, 2017, and 2019, and a diver-operated hyperspectral imager (i.e., DiveRay) was used to survey the same transects in 2019. Machine learning algorithms were used to develop an automated pipeline to assess the benthic cover of 10 biotic and abiotic categories in 2019 based on hyperspectral imagery. The cover of scleractinian corals did not differ between 2015 and 2017 despite being subjected to a series of environmental disturbances in these years. Surveys in 2019 documented the almost complete decline of the habitat-defining staghorn coral Acropora abrotanoides (a practically complete disappearance from about 10% cover), a significant decrease (~75%) in the cover of other scleractinian corals, and a significant increase (~55%) in the combined cover of bare substrate, turf algae, and cyanobacteria. The drastic change in community composition suggests that the reef at Lafac Bay is transitioning to a turf algae-dominated community. However, the capacity of this reef to recover from previous disturbances suggests that this transition could be reversed, making Lafac Bay an excellent candidate for long-term monitoring. Community analyses showed no significant difference between automatically classified benthic cover estimates derived from the hyperspectral scans in 2019 and those derived from photoquadrats. These findings suggest that underwater hyperspectral imagers can be efficient and effective tools for fast, frequent, and accurate monitoring of dynamic reef communities.

Systematic review of the uncertainty of coral reef futures under climate change

Climate change impact syntheses, such as those by the Intergovernmental Panel on Climate Change, consistently assert that limiting global warming to 1.5 °C is unlikely to safeguard most of the world's coral reefs. This prognosis is primarily based on a small subset of available models that apply similar 'excess heat' threshold methodologies. Our systematic review of 79 articles projecting coral reef responses to climate change revealed five main methods. 'Excess heat' models constituted one third (32%) of all studies but attracted a disproportionate share (68%) of citations in the field. Most methods relied on deterministic cause-and-effect rules rather than probabilistic relationships, impeding the field's ability to estimate uncertainty. To synthesize the available projections, we aimed to identify models with comparable outputs. However, divergent choices in model outputs and scenarios limited the analysis to a fraction of available studies. We found substantial discrepancies in the projected impacts, indicating that the subset of articles serving as a basis for climate change syntheses may project more severe consequences than other studies and methodologies. Drawing on insights from other fields, we propose methods to incorporate uncertainty into deterministic modeling approaches and propose a multi-model ensemble approach to generating probabilistic projections for coral reef futures.

Rarity mediates species-specific responses of tropical reef fishes to protection

Marine protected areas (MPAs) are the most widely applied tool for marine biodiversity conservation, yet many gaps remain in our understanding of their species-specific effects, partly because the socio-environmental context and spatial autocorrelation may blur and bias perceived conservation outcomes. Based on a large data set of nearly 3000 marine fish surveys spanning all tropical regions of the world, we build spatially explicit models for 658 fish species to estimate species-specific responses to protection while controlling for the environmental, habitat and socio-economic contexts experienced across their geographic ranges. We show that the species responses are highly variable, with ~40% of fishes not benefitting from protection. When investigating how traits influence species' responses, we find that rare top-predators and small herbivores benefit the most from MPAs while mid-trophic level species benefit to a lesser extent, and rare large herbivores experience adverse effects, indicating potential trophic cascades.

Functional potential and evolutionary response to long-term heat selection of bacterial associates of coral photosymbionts

IMPORTANCE

Symbiotic microorganisms are crucial for the survival of corals and their resistance to coral bleaching in the face of climate change. However, the impact of microbe-microbe interactions on coral functioning is mostly unknown but could be essential factors for coral adaption to future climates. Here, we investigated interactions between cultured dinoflagellates of the Symbiodiniaceae family, essential photosymbionts of corals, and associated bacteria. By assessing the genomic potential of 49 bacteria, we found that they are likely beneficial for Symbiodiniaceae, through the production of B vitamins and antioxidants. Additionally, bacterial genes involved in host-symbiont interactions, such as secretion systems, accumulated mutations following long-term exposure to heat, suggesting symbiotic interactions may change under climate change. This highlights the importance of microbe-microbe interactions in coral functioning.

Insights from the 2-year-long human confinement experiment in Grand Cayman reveal the resilience of coral reef fish communities

In March 2020, the world went into lockdown to curb the spread of the novel coronavirus (SARS-CoV-2), with immediate impacts on wildlife across ecosystems. The strict 2-year long lockdown in Grand Cayman provided an unprecedented opportunity to assess how the 'human confinement experiment' influenced the community composition of reef fish. Using a suite of multivariate statistics, our findings revealed a stark increase in reef fish biomass during the 2 years of lockdown, especially among herbivores, including parrotfish, with drastic increases in juvenile parrotfishes identified. Additionally, when comparing baseline data of the community from 2018 to the 2 years during lockdown, over a three-fold significant increase in mean reef fish biomass was observed, with a clear shift in community composition. Our findings provide unique insights into the resilience of reef fish communities when local anthropogenic stressors are removed for an unprecedented length of time. Given the functional role of herbivores including parrotfish, our results suggest that reductions in human water-based activities have positive implications for coral reef ecosystems and should be considered in future management strategies.

Assessing the contribution of bacteria to the heat tolerance of experimentally evolved coral photosymbionts

Coral reefs are extremely vulnerable to ocean warming, which triggers coral bleaching-the loss of endosymbiotic microalgae (Symbiodiniaceae) from coral tissues, often leading to death. To enhance coral climate resilience, the symbiont, Cladocopium proliferum was experimentally evolved for >10 years under elevated temperatures resulting in increased heat tolerance. Bacterial 16S rRNA gene metabarcoding showed the composition of intra- and extracellular bacterial communities of heat-evolved strains was significantly different from that of wild-type strains, suggesting bacteria responded to elevated temperatures, and may even play a role in C. proliferum thermal tolerance. To assess whether microbiome transplantation could enhance heat tolerance of the sensitive wild-type C. proliferum, we transplanted bacterial communities from heat-evolved to the wild-type strain and subjected it to acute heat stress. Microbiome transplantation resulted in the incorporation of only 30 low-abundance strains into the microbiome of wild-type cultures, while the relative abundance of 14 pre-existing strains doubled in inoculated versus uninoculated samples. Inoculation with either wild-type or heat-evolved bacterial communities boosted C. proliferum growth, although no difference in heat tolerance was observed between the two inoculation treatments. This study provides evidence that Symbiodiniaceae-associated bacterial communities respond to heat selection and may contribute to coral adaptation to climate change.

Artificial light at night (ALAN) disrupts behavioural patterns of reef corals

Increasing levels of Artificial Light At Night (ALAN) alter the natural diel cycles of organisms at global scale. ALAN constitutes a potential threat to the light-dependent functioning of symbiotic scleractinian corals, the habit-founders of warm, shallow water reefs. Here, we show that ALAN disrupts the natural diel tentacle expansion and contraction behaviour, a key mechanism for prey capture and nutrient acquisition in corals. We exposed four symbiotic scleractinian coral species to different ALAN treatments (0.4-2.5 μmol quanta m-2 s-1). Exposure to ALAN levels of 1.2 μmol quanta m-2 s-1 and above altered the normal tentacle expansion response in diurnal species (Stylophora pistillata and Duncanopsammia axifuga). The tentacle expansion pattern of nocturnal species (Montastraea cavernosa and Lobophyllia hemprichii) was less affected, which may indicate a greater capacity to tolerate ALAN exposure. The results of this work suggest that ALAN has the potential to affect nutrient acquisition mechanisms of symbiotic corals which may in turn result in changes in the coral community structure in shallow water reefs in ALAN-exposed areas.

Plastic pollution on the world's coral reefs

Coral reefs are losing the capacity to sustain their biological functions1. In addition to other well-known stressors, such as climatic change and overfishing1, plastic pollution is an emerging threat to coral reefs, spreading throughout reef food webs2, and increasing disease transmission and structural damage to reef organisms3. Although recognized as a global concern4, the distribution and quantity of plastics trapped in the world's coral reefs remains uncertain3. Here we survey 84 shallow and deep coral ecosystems at 25 locations across the Pacific, Atlantic and Indian ocean basins for anthropogenic macrodebris (pollution by human-generated objects larger than 5 centimetres, including plastics), performing 1,231 transects. Our results show anthropogenic debris in 77 out of the 84 reefs surveyed, including in some of Earth's most remote and near-pristine reefs, such as in uninhabited central Pacific atolls. Macroplastics represent 88% of the anthropogenic debris, and, like other debris types, peak in deeper reefs (mesophotic zones at 30-150 metres depth), with fishing activities as the main source of plastics in most areas. These findings contrast with the global pattern observed in other nearshore marine ecosystems, where macroplastic densities decrease with depth and are dominated by consumer items5. As the world moves towards a global treaty to tackle plastic pollution6, understanding its distribution and drivers provides key information to help to design the strategies needed to address this ubiquitous threat.

Research priorities for the sustainability of coral-rich western Pacific seascapes

Nearly a billion people depend on tropical seascapes. The need to ensure sustainable use of these vital areas is recognised, as one of 17 policy commitments made by world leaders, in Sustainable Development Goal (SDG) 14 ('Life below Water') of the United Nations. SDG 14 seeks to secure marine sustainability by 2030. In a time of increasing social-ecological unpredictability and risk, scientists and policymakers working towards SDG 14 in the Asia-Pacific region need to know: (1) How are seascapes changing? (2) What can global society do about these changes? and (3) How can science and society together achieve sustainable seascape futures? Through a horizon scan, we identified nine emerging research priorities that clarify potential research contributions to marine sustainability in locations with high coral reef abundance. They include research on seascape geological and biological evolution and adaptation; elucidating drivers and mechanisms of change; understanding how seascape functions and services are produced, and how people depend on them; costs, benefits, and trade-offs to people in changing seascapes; improving seascape technologies and practices; learning to govern and manage seascapes for all; sustainable use, justice, and human well-being; bridging communities and epistemologies for innovative, equitable, and scale-crossing solutions; and informing resilient seascape futures through modelling and synthesis. Researchers can contribute to the sustainability of tropical seascapes by co-developing transdisciplinary understandings of people and ecosystems, emphasising the importance of equity and justice, and improving knowledge of key cross-scale and cross-level processes, feedbacks, and thresholds.