Coral reefs under rapid climate change and ocean acidification

Design of Ni-FAU Zeolite Bifunctional Materials for Integrated Carbon Dioxide Capture and Methanation: Construction of ultrafine NiO nanoparticles

The Integrated Carbon Dioxide (CO2) Capture and Methanation (ICCU-Met) technology has emerged as a promising strategy for reducing CO2 emissions while producing methane (CH4) fuel. However, a significant challenge in this process is the absence of bifunctional materials (DFMs) that simultaneously possess highly dispersed metal sites and stable adsorbent structures under variable temperature conditions. This is particularly problematic because existing nickel-based (Ni) bifunctional materials are prone to metal sintering and structural degradation at high temperatures. In this study, highly dispersed ultrafine Ni metal confined in Faujasite (FAU) zeolite support bifunctional materials were synthesized with remarkable CO2 capture capacity of 2.77 mmol CO2/g and CH4 yield of 654.4 μmol CH4/g in the ICCU-Met reaction. Notably, the 8Ni-FAU DFMs maintained their initial activity after 10 drastic heating-cooling cycles between 70 °C and 300 °C. Moreover, the CO2 adsorption, CH4 yield, and CH4 selectivity of 8Ni-FAU DFMs under simulated real flue gas atmosphere were 0.43 mmol/g, 264.3 μmol/g, and 99.5 %, respectively. This stability is attributed to the successful immobilization of ultrafine NiO nanoparticles within the FAU zeolite pores, which enhanced the metal-support interactions and promoted the formation of oxygen vacancies. These features facilitated the efficient adsorption and decomposition of CO2, as well as the activation and dissociation of H2. Both in situ DRIFTs experiments and density functional theory (DFT) calculations confirmed that the 8Ni-FAU DFMs proceed via the formate pathway. Additionally, it was found that the strong interaction between the active Ni metal and the FAU support reduces the CO2 adsorption energy and lowers the energy barrier for the generation of formate (HCOO*) active intermediates, thus guiding the ICCU-Met reaction.

Fostering marine resilience through the reduction of anthropogenic pressures in temperate rocky reefs

Resilience is vital for maintaining the health of temperate coastal systems, especially in the Anthropocene era, where anthropogenic pressures such as pollution, physical impacts, and overfishing pose significant threats. However, the scarcity of studies addressing marine resilience hampers its effective management. To address this issue, we evaluated the resilience of 300 temperate rocky reefs situated in Southern Europe, considering biological, environmental, and anthropogenic factors. We identified 43 top resilient areas recommended for conservation and 39 bottom resilient areas that could benefit from reducing anthropogenic pressures. Given that our findings suggest that anthropogenic pressures unequally influence the resilience of bottom resilient areas, we followed their decreasing order of influence to simulate five management scenarios based on the cumulative reduction of these pressures. While different percentages of reduction in anthropogenic pressures were necessary to significantly enhance resilience in each scenario, we found that, regardless of the approach taken, a comparable percentage of bottom resilient areas-ranging from 17 % to 23 %-could be reclassified as moderate resilient areas. By advancing resilience knowledge in temperate rocky reefs, this research underscores the important role that reducing anthropogenic pressures plays in enhancing resilience but also provides valuable insights for their strategic management.

Impact of iron exposure on Brazilian coral reefs: Acute vs. chronic stress responses

Prior research has shown that exposure to metals increases corals vulnerability to bleaching by heightened oxidative stress. Understanding the impact of metal contamination on coral health in their natural environmental is crucial. This study investigate the effects of iron (Fe) exposure on Brazilian coral reef species. We evaluated the response of Mussismilia harttii, Millepora alcicornis, and Siderastrea sp. to acute (4 days) and chronic (28 days) Fe exposure under environmentally relevant concentrations (0, 100, 300 and 900 μg L-1). Experiments were conducted in laboratory and in a marine mesocosm Biomarkers including Fe bioaccumulation, lipid peroxidation (LPO), protein carbonylation (PCN), and DNA damage were measured. The correlation between chronic exposure results and environmental factors were also analyzed. The hypotheses were: a) Fe exposure would increase ROS production in corals, leading to biomolecule damage; b) acute and chronic Fe exposure would affect ROS production and biomolecule damage differently; c) Fe bioaccumulation would vary between species and concentrations; and d) environmental factors might influence coral responses to Fe. Results indicated that all species exhibited increased Fe bioaccumulation as metal concentrations increased, suggesting a common ability to absorb and accumulate Fe. The oxidative damage response vired between acute and chronic exposure, with acute exposure causing more damage while chronic exposure showed a temporal reduction in damage. Environmental factors (e.g. temperature, pH, salinity and dissolved oxygen) also influenced the coral responses, either exacerbating or mitigating oxidative stress effects. These findings highlight the importance of understanding Fe contamination impacts for the conservation of Brazilian coral reefs.

Laboratory experiments revealed different bleaching susceptibilities to heat stress in eight species of subtropical urban corals

Understanding species' susceptibility to environmental stressors is crucial for conservation planning, but such data are unavailable for many subtropical corals. We therefore conducted 1-month laboratory experiments to determine the heat stress susceptibility of eight species from subtropical areas by exposing them to 32 °C (treatment) or 25 °C (control). Four species (Dipsastraea rotumana, Echinophyllia aspera, Pavona decussata, and Platygyra carnosa) survived the whole experiment, although bleaching occurred after one to two weeks of exposure. The heat exposure caused total mortality in the other four species: on day 2 in Acropora solitaryensis, day 7 in Acropora digitifera, day 9 in Acropora pruinosa, and day 17 in Montipora peltiformis. These results suggest that repeated heatwaves may cause changes in coral communities by causing disproportionally high mortality of heat-sensitive species. Coral species tested in this study, collected from subtropical reefs previously thought to be refuges for coral reefs under global warming, demonstrated greater susceptibility to heat stress than their tropical counterparts. This raises concerns about the persistence of coral reefs as sea surface temperatures continue to rise.

Spatially restricted coral bleaching as an ecological manifestation of within-colony heterogeneity

Coral bleaching is a widespread stress response of reef-building corals to elevated sea temperatures, resulting in the loss of symbiotic algae and often leading to coral death and reef degradation. Although coral bleaching occurs globally, not all reefs, species, colonies, or polyps bleach equally. Understanding intra-colony bleaching heterogeneity is crucial to anticipate the extent of coral loss at 2°C warming and harness variability to inform restorative interventions. Partially bleached coral colonies are commonly documented yet rarely tracked to determine whether they reflect ecologically distinct heterogeneity (e.g., in thermal tolerance) or eventually bleach completely. Focusing on bleaching that appears restricted to certain areas within a coral colony, we examine its putative basis in the spatial variability of the holobiont. A coral's three-dimensional structure creates mosaics of microenvironments. Adaptations to these microenvironments are underpinned by intra-colony differences in Symbiodiniaceae association, microbiome assemblage, and nutritional status, giving rise to microhabitats. Genetic mosaicism and epigenetic changes further contribue to intra-colony phenotypic heterogeneity. We pinpoint methodologies to align spatially restricted bleaching to different forms of coral surface heterogeneity, examine the common assumption that coral fragments represent entire colonies, and illuminate implications for coral biology and restoration.

Quantifying the impact of future climate change on the risk of coral rubble instability across the Great Barrier Reef by 2100

Coral reef systems are facing unprecedented pressures due to climate change, and stable coral rubble substrates are crucial for facilitating large-scale coral regeneration. This study integrates the Sixth Phase of the Coupled Model Intercomparison Project climate models, sea-level rise projections from the Intergovernmental Panel on Climate Change Sixth Assessment Report, Shared Socioeconomic Pathway scenarios, and applies machine learning techniques to assess the risk of coral rubble instability in the Great Barrier Reef under future wave climate and depth change scenarios. Using the EC-Earth climate model under the SSP5-8.5 scenario-calibrated with data from 41 synoptic stations-we estimated various climate data for 2031-2100 and examined the impact of key factors such as wave climate and depth changes on the risk of coral instability. Coral rubble instability risk depends on future wave climate and depth changes from sea-level rise and deposition. Future changes in wave climate are expected to increase the risk of instability, while increased depth mitigates these destabilizing effects. Over the next 70 years, most areas of the Great Barrier Reef are projected to experience stable or decreasing risk of coral rubble instability. The proportion of no-risk areas is higher in the northern regions, whereas the far southern regions have fewer no-risk areas and more high-risk zones. High-risk and very high-risk areas are mainly concentrated along reef edges, reefs facing the Pacific Ocean, and shallow waters near the shoreline. The transition between high-risk and low-risk areas is gradual rather than abrupt. Annual projections align with long-term trends: coral rubble remains relatively stable in the northern and central regions, which is more conducive to future coral recovery. However, the persistent presence of high-risk and very high risk areas poses significant challenges to coral recovery in the far southern region. By providing insights into the spatial and temporal evolution of coral rubble instability risk, this study aims to support decision-makers, environmental scientists and researchers in formulating appropriate interventions to enhance the resilience of coral reefs under changing environmental conditions.

Mesophotic reefs offer thermal refuge to the 2023 Caribbean mass bleaching event in the Cayman Islands

Coral reefs are increasingly threatened by marine heatwaves, which drive widespread coral bleaching and mortality. Mesophotic coral ecosystems (MCEs) have been proposed as potential thermal refuges due to their greater depth and relative isolation from surface temperature extremes. Yet their resilience to extreme heat events remains uncertain, with location specific conclusions, thus requiring further studies. Here, we investigate the effects of the 2023 marine heatwave in the Cayman Islands, which resulted in prolonged sea surface temperatures exceeding 31 °C and 17.5 DHW with extensive bleaching across shallow coral reefs. Utilizing vertical transect surveys from 10 m to 50 m, we assessed depth-related variations in bleaching prevalence and temperature profiles. Our results indicate a significant decline in bleaching with increasing depth, with a concurrent reduction in temperature. Depth-generalist species exhibited reduced bleaching at greater depths, whereas shallow-water specialists displayed severe bleaching. These findings suggest that while MCEs may provide thermal refuge for some species, their capacity to buffer against climate-driven reef degradation is species-specific. Given the increasing frequency and intensity of marine heatwaves, understanding the role of deeper reef habitats in mitigating coral loss is critical for informing conservation and management strategies. Our study underscores the importance of protecting MCEs as potential thermal refuges while emphasizing the need for continued research on species-specific thermal resilience with depth.

Complete mitochondrial genome of the brain coral Platygyra daedalea (Ellis & Solander, 1786)

Platygyra daedalea Ellis & Solander, 1786, is a dominant species within the world's warmest reefs, making it a critical model for investigating coral stress resistance and adaptive evolutionary mechanisms. This study presents the first sequenced and annotated mitogenome of the reef-building coral P. daedalea. The mitogenome is 16,363 bp in length, containing 13 protein-coding genes, two ribosomal RNA genes, and two transfer RNA genes. The base composition is 24.8% adenine (A), 13% cytosine (C), 20.4% guanine (G), and 41.8% thymine (T), with a G-C content of 33.4%. We conducted a comparative analysis between P. daedalea and P. carnosa. Notably, genetic variations in the ND5 and COXI genes emerge as potential markers for distinguishing species within the Platygyra genus. Additionally, the protein-coding gene ND6 has been subjected to strong selective pressure. Phylogenetic analysis based on the complete mitogenome aligns with the internal clade structure of Scleractinia reported in previous studies, reinforcing the evolutionary insights provided by this dataset.

Between shells and seas: Effects of ocean acidification on calcification and osmoregulation in yellow clam (Amarilladesma mactroides)

The decline in ocean pH due to rising CO2 levels is a critical factor impacting marine ecosystems. Ocean acidification (OA) is expected to negatively affect various organisms, particularly those with mineralized structures. While the effects of OA on the calcification of shells and exoskeletons are documented, the impact on homeostatic processes, such as osmoregulation, is less understood. Osmoregulation is vital for maintaining water and salt balance within marine organisms, crucial for their survival and physiological functions. Acidification may alter ion exchange mechanisms, affecting the regulation of ions. In this study, we evaluated the effects of intermediate OA (pH 7.6) with or without hypersaline stress (35‰) on calcification and osmotic balance biomarkers in the bivalve Amarilladesma mactroides after 96h of acute exposure. We found that pH did not affect hemolymph osmolality or extracellular Ca2+ concentration. However, OA impaired the bivalve's ability to maintain its mineralized structures by decreasing Ca2+-ATPase enzyme activity in the mantle. The increase in carbonic anhydrase activity indicated a specific response to maintain acid-base balance in the tissue, i.e., compensating for the effects of acidification by neutralizing CO2 accumulation and stabilizing internal pH. In the gills, both enzymes showed increased performance under higher salinity and reduced pH. Exposure to less alkaline pH inhibited carbonic anhydrase and Na+/K+-ATPase activity, potentially affecting the regulation of essential inorganic osmolytes.

Evaluating the global sea snake diversity and distribution under climate change scenario

Anthropogenically accelerated climate change has wreaked havoc on marine ecosystems, particularly affecting marine reptiles such as sea snakes. These reptiles are highly sensitive to climate change induced coral reef degradation and environmental fluctuations, leading to habitat expansion and increased human-sea snake interactions. Despite this, till date no comprehensive investigation of global sea snake diversity and distribution has been conducted. In this study, we used MaxEnt Species Distribution Modelling (SDM) to assess effects of climate change on sea snake distribution from 1993 to 2024. This analysis integrates occurrence data sourced from exhaustive literature reviews and biogeographic databases with environmental predictors like seawater temperature, salinity, and chlorophyll a concentration. The study identifies 74 species across 11 genera and 3 families. Among 14 biogeographic habitats examined, the South Pacific and Indian Oceans exhibit highest species richness, while the Atlantic Ocean shows the lowest. Notably, species in the Bay of Bengal and Arafura Sea demonstrate significant taxonomic distinctness. Furthermore, our findings reveal a substantial expansion of sea snake habitats from equatorial to temperate regions, primarily driven by increase in seawater temperature. Optimal habitat suitability is associated with temperatures of approximately 30 °C, chlorophyll a concentration of around 0.3 mg m-3, and salinity levels between 35 and 40 g L-1. These insights into sea snake diversity and distributional shifts induced by global climate change are critical for formulating evidence-based management strategies, including implementation of sustainable fishing practices, preservation of critical habitats, and establishment of rigorous bycatch mitigation protocols to ensure conservation of these ecologically significant marine reptiles.

Phosphorus addition mitigates the combined negative effects of high temperature and nitrogen stress on corals

Global warming and imbalances in nitrogen (N)-phosphorus (P) ratios due to increased human activity have had significant impacts on coral reef ecosystems. However, the underlying mechanisms of these impacts remain poorly understood. In this study, a controlled experiment was conducted on Acropora hyacinthus treated with different P concentrations at high temperature (30 °C) and high N level (9 μM nitrate), which was analyzed in terms of physical observations and physiological indices, as well as photosynthetic activity and fatty acid composition. The results indicated that nitrate enrichment significantly reduced Symbiodiniaceae density, total chlorophyll content, and photosynthetic efficiency, as well as notable coral bleaching. P addition alleviated some of these detrimental effects, enhancing symbiotic relationship and maintaining photosynthetic activity. Additionally, changes in fatty acid composition suggest that P supplementation may improve coral tolerance to the combined stress of heat stress and nitrate enrichment by enhancing coral heterotrophy. These findings underscore the importance of balanced nutrient ratio for corals and propose P supplementation as a potential strategy to mitigate the combined stress on coral reefs.

Metabolic Shifts and Muscle Remodeling as Pro-Survival and Energy Compensation Strategies in Photosymbiotic Giant Clams after Bleaching

Tropical photosymbiotic giant clams are increasingly threatened by climate change, leading to widespread bleaching. Decline in density of symbionts caused mortality events in symbiotic organisms; however, giant clams appear to exhibit prior survival capacity against these detrimental effects. It remains unclear whether giant clams can mitigate the adverse impacts of bleaching. Herein, we found that bleaching events after chronic heat stress induce remarkable changes and remodeling in symbiotic tissue of the giant clam Tridacna crocea. The density and structure of unique muscle fibers with high collagen content, observed in siphonal mantle of these animals, were negatively altered after heat stress. These changes were associated with a metabolic shift from carbohydrates and fatty acids to amino acids as the breakdown of collagen-rich muscle fibers can partially compensate for energy loss during bleaching. Such a shift was proposed to be regulated by AMP-activated protein kinase (AMPK) signaling and FoxO-atrogin pathways. Overall, our study highlights a pro-survival mechanism in giant clams through plastic regulation, which likely contributes to their relatively high environmental resilience during bleaching.

How environmental stochasticity can destroy the persistence of macroalgae in a coral reefs ecosystem

In this study, we mainly investigate how environmental stochasticity can destroy the persistence of macroalgae in a coral reefs ecosystem by analyzing the noise-induced tipping behavior. Firstly, detailed mathematical analysis for all feasible system parameters shows that the deterministic system has rich dynamics, including two types of bifurcations and two types of bistabilities. This also reveals that the dynamic behavior of coral reefs ecosystem could be highly sensitive to the system parameters and initial values. For the stochastic system, two kinds of noise-induced tipping behaviors are numerically found: Transition from coral-free state to macroalgae-free state; transition from coexistence state to macroalgae-free state. We then mainly analyze the impacts of noise intensity on the probability and time that coral reef ecosystem tips between different states, evaluate the extinction risk of macroalgae for different initial values, and eventually assign extinction warning levels to these values. Our analysis reveals that as a fragile marine ecosystem, the evolution trend of the coral reefs depends not only on the system parameters and initial values, but also on the intensity of the stochasticity experienced by the system.

Symbiont-Mediated Metabolic Shift in the Sea Anemone Anthopleura elegantissima

Coral reefs and their photosynthetic algae form one of the most ecologically and economically impactful symbioses in the animal kingdom. The stability of this nutritional mutualism and this ecosystem is, however, at risk due to increasing sea surface temperatures that cause corals to expel their symbionts. Symbioses with these microeukaryotes have independently evolved multiple times, and non-coral cnidarians (e.g., sea anemones) serve as a valuable and insightful comparative system due to their ease of husbandry in the laboratory and their ability to shuffle different strains of their photosymbionts to acclimate to thermal conditions. This breadth of symbiont shuffling is exemplified by the sea anemone Anthopleura elegantissima , which naturally occurs in symbiosis with the dinoflagellate Breviolum muscatinei (formerly Symbiodinium) or the chlorophyte Elliptochloris marina as well as being aposymbiotic. Here, we assembled a draft genome and used multi-omics to characterise multiple physiological levels of each phenotype. We find that A. elegantissima has symbiont-specific transcriptional and metabolomic signatures, but a similar bacterial community dominated by a single Sphingomonas species that is commonly found in the cnidarian microbiome. Symbiosis with either eukaryotic symbiont resulted in differential gene expression and metabolic abundance for diverse processes spanning metabolism and immunity to reproduction and development, with some of these processes being unique to either symbiont. The ability to culture A. elegantissima with its phylogenetically divergent photosymbionts and perform experimental manipulations makes A. elegantissima another tractable sea anemone system to decode the symbiotic conversations of coral reef ecosystems and aid in wider conservation efforts.

Current velocity, water quality, and benthic taxa as predictors for coral recruitment rates on the Great Barrier Reef

Coral reefs worldwide are experiencing frequent disturbances, rendering coral recruitment critical for population recovery. This large-scale study identifies environmental, spatial, and biotic drivers of coral recruit densities at 141 stations stratified across seven regions and three depths (1, 5, and 15 m depths) with contrasting environmental conditions across and along the Great Barrier Reef and the Torres Strait. Settlement tiles were deployed for two years, with coral densities and benthic cover quantified following retrieval. Benthic communities were assessed from tile images using the point-classification AI program ReefCloud. Environmental data were derived from in situ readings and environmental models. Across all sites, coral recruit densities averaged 187 ±  12 m‒2 (SE), with region-wide averages ranging from 43.5 ±  12 m‒2 to 247 ±  32 m‒2. Mean densities were 3-fold higher in the four clear-water regions compared to the three turbid-water regions. Boosted regression tree analyses showed that densities declined with increasing current velocity, sedimentation, and depth, and increased with increasing pH. From lowest to highest observed levels of current velocity, recruit densities declined by ~ 530 m‒2. From lowest to highest sedimentation, densities declined by ~ 300 recruits m‒2. Even relatively minor increases in sediment deposits from 0.1 to 38 mg cm‒2 were associated with a monotonic decline of ~ 130 recruits m‒2. Recruit densities were also weakly positively related to the cover of turf and crustose coralline algae on tile tops, and negatively related to fleshy invertebrate cover on the tile undersides. Some variation in the cover of these benthic taxa was also related to environmental conditions (e.g., sedimentation and currents), suggesting the possibility of additional indirect environmental effects on recruit densities. Our results highlight the strong role of current velocity and water quality as regulators of coral recruitment success, likely influencing the capacity of reef sites to recover after a disturbance.

Ecosystem Service Trajectories in Restored Coastal Habitats

Ecosystem restoration is urgently needed to restore, maintain, or increase valued ecosystem services provided by natural habitats. However, the provision of services in restored habitats, in comparison to natural, undegraded habitats, and the time required for them to be generated, is uncertain. Here, for the first time in coastal (or to our knowledge, any) ecosystems, we systematically outline why and how to characterize pathways of ecosystem service recovery following restoration. Using real-world and theoretical examples, mainly from coastal habitats, we outline seven key components required to characterize ecosystem service trajectories. These components are the baseline rate and variability of ecosystem service provisioning, and the trend type, direction, rate, time to natural equivalence and variability of restored ecosystem service provisioning. These components provide novel insights into the development of ecosystem services and values over time, and their use can help in planning on-ground restoration projects and monitoring regimes, valuing ecosystem services, and determining restoration success.

'Neither here nor there'? Meiofauna as an effective tool to evaluate the impacts of the 2019 mysterious oil spill in a Northeast Brazil coral reef

During the last half of 2019, the Northeast coast of Brazil suffered from an extensive oil spill of unknown origin, and marine organisms in those areas were subjected to significant impacts. In situations like this, the contaminant effects can persist for varying periods. Oil contaminants, such as polycyclic aromatic hydrocarbons (PAHs), generally reduce taxa's abundance and diversity in benthic communities in areas with greater exposure to chemical components. Meiofaunal organisms are excellent indicators of impacts caused by oil spills due to their holobenthic strategy, short life cycle, high taxonomic diversity, and the use of various microhabitats. Thus, we aim to evaluate the impact of the 2019 oil spill by comparing the meiofauna of a strongly impacted coral reef area (Cupe Reef) and an unaffected reef area (Serrambi Reef). The latter considered a control area in our study. Since pre-impact data was unavailable for the Cupe Reef, an in situ limited experiment was run to simulate a small local and immediate impact of oil on the control reef. We used synthetic grass mats as an artificial substrate unit (ASU) to colonize meiofauna. Our results suggest that the tar-like oil that hit the Brazilian coast in late 2019 affected the coral reef meiofauna community. We show that its effect was still evident a few years after the oil spill. The use of ASU as a standardized substrate for colonization and a sampling design that controls for within-reef spatial variability (pools) enabled us to determine impacts at different taxonomic resolutions. The measured impact is equivalent to that caused by a metropolitan region with more than four million inhabitants and with a discharge of several heavily polluted rivers in nearby reefs. Furthermore, our results largely agree with the literature suggesting a higher sensitivity of Copepoda compared to Nematoda, the main taxa of meiofauna.

Impacts of a prolonged marine heatwave and chronic local human disturbance on juvenile coral assemblages

Coral reefs are threatened by climate change and chronic local human disturbances. Although some laboratory studies have investigated the effects of combined stressors, such as nutrient enrichment and heat stress, on growth and survival of early life stage corals, in situ studies remain limited. To assess the influence of multiple stressors on juvenile corals, we quantified densities of corals ≤ 5 cm at 18 forereef sites with different exposure levels to underlying chronic local human disturbance before, during, and after the 2015-2016 El Niño. This marine heatwave caused prolonged heat stress and devastating losses of coral cover on the shallow forereef's of Kiritimati, in the central equatorial Pacific Ocean. Here, we enumerated a total of 7732 juvenile corals from 13 different families. Over 80% of corals were from four families: 70% from Agariciidae, Merulinidae, or Poritidae, which all have stress-tolerant life history strategies, and 11% from Acroporidae which has a competitive life-history strategy. Both local disturbance and heat stress were significantly negatively related to juvenile coral densities. Prior to the heatwave, juvenile densities were on average 72% lower at the most disturbed sites (7.2 ±  1.9 m-2) compared to the least disturbed ones (15.3 ±  3.8 m-2). Overall, juvenile corals had a lower bleaching prevalence and lower mortality during the heatwave when compared to their adult counterparts. Still, the heatwave resulted in the loss of half (49%) of all juvenile corals, with those corals with competitive or weedy life history strategies undergoing greater declines than stress-tolerant ones. Although juvenile coral densities increased slightly in the year following the heatwave, the effect was statistically non-significant. Our results highlight the influence of chronic local anthropogenic and marine heatwaves on juvenile coral densities.

Nitrogen source type modulates heat stress response in coral symbiont (Cladocopium goreaui)

Ocean warming due to climate change endangers coral reefs, and regional nitrogen overloading exacerbates the vulnerability of reef-building corals as the dual stress disrupts coral-Symbiodiniaceae mutualism. Different forms of nitrogen may create different interactive effects with thermal stress, but the underlying mechanisms remain elusive. To address the gap, we measured and compared the physiological and transcriptional responses of the Symbiodiniaceae Cladocopium goreaui to heat stress (31°C) when supplied with different types of nitrogen (nitrate, ammonium, or urea). Under heat stress (HS), cell proliferation and photosynthesis of C. goreaui declined, while cell size, lipid storage, and total antioxidant capacity increased, both to varied extents depending on the nitrogen type. Nitrate-cultured cells exhibited the most robust acclimation to HS, as evidenced by the fewest differentially expressed genes (DEGs) and less ROS accumulation, possibly due to activated nitrate reduction and enhanced ascorbate biogenesis. Ammonium-grown cultures exhibited higher algal proliferation and ROS scavenging capacity due to enhanced carotenoid and ascorbate quenching, but potentially reduced host recognizability due to the downregulation of N-glycan biosynthesis genes. Urea utilization led to the greatest ROS accumulation as genes involved in photorespiration, plant respiratory burst oxidase (RBOH), and protein refolding were markedly upregulated, but the greatest cutdown in photosynthate potentially available to corals as evidenced by photoinhibition and selfish lipid storage, indicating detrimental effects of urea overloading. The differential warming nitrogen-type interactive effects documented here has significant implication in coral-Symbiodiniaceae mutualism, which requires further research.IMPORTANCERegional nitrogen pollution exacerbates coral vulnerability to globally rising sea-surface temperature, with different nitrogen types exerting different interactive effects. How this occurs is poorly understood and understudied. This study explored the underlying mechanism by comparing physiological and transcriptional responses of a coral symbiont to heat stress under different nitrogen supplies (nitrate, ammonium, and urea). The results showed some common, significant responses to heat stress as well as some unique, N-source dependent responses. These findings underscore that nitrogen eutrophication is not all the same, the form of nitrogen pollution should be considered in coral conservation, and special attention should be given to urea pollution.

Diversity and dynamics of multiple symbionts contribute to early development of broadcast spawning reef-building coral Dipsastraea veroni

Sexual reproduction and recruitment enhance the genetic diversity and evolution of reef-building corals for population recovery and coral reef conservation under climate change. However, new recruits are vulnerable to physical changes and the mechanisms of symbiosis establishment remain poorly understood. Here, Dipsastraea veroni, a broadcast spawning hermaphrodite reef-building coral, was subjected to settlement and juvenile growth in flow-through in situ seawater at 27.93 ± 0.96°C. Symbiosis of Symbiodiniaceae, bacteria, and/or archaea by horizontal acquisition and/or hypothetical vertical transmission through the mucus with symbionts from the parent appears to be a heritable process of selection and adaptation in D. veroni at the egg, larva, juvenile (5 days post settlement, d p.s. and 32 d p.s.) stages. Symbiodiniaceae was dominated by the genera Cladocopium, Durusdinium, Symbiodinium, with increasing relative abundance of Durusdinium at 5 d p.s. and Symbiodinium at 32 d p.s. Mixed acquisition of the dominant phyla Pseudomonadota, Bacteroidota, Cyanobacteriota, Bacillota, Planctomycetota, and Actinomycetota in egg, larva, and/or juvenile showed a winnowing and regulated bacterial diversity and dynamics, resulting in stage-abundant orders Pseudomonadales and Bacillales in egg and Rhodobacterales, Rhodospirillales, Cyanobacteria, and Cyanobacteriales in larva and/or juvenile. The photoautotrophic Chloroflexales, Cyanobacteriales, and Chlorobiales were abundant in adults. The stable archaeal community contained predominant Crenarchaeota, Halobacterota, Nanoarchaeia Thermoplasmatota, and eight rare phyla, with increased relative abundance of the genera Bathyarchaeota, Candidatus_Nitrosopumilus, Candidatus_Nitrocosmicus, Nitrosarchaeum, Candidatus_Nitrosotenuis, Candidatus_Nitrosopelagicus, Cenarchaeum, Haladaptatus, Halogranum, Halolamina, and Woesearchaeales and GW2011-AR15 in juveniles. All results revealed flexible symbiotic mechanisms in D. veroni during early ontogeny for coral survival and evolution.IMPORTANCEFlexible symbioses of Symbiodiniaceae, bacteria, and archaea appear to be a heritable process of selection and adaptation in Dipsastraea veroni in the field, benefiting early coral development and facilitating coral population recovery and reef conversation.

Cryptic coral community composition across environmental gradients

Cryptic genetic variation is increasingly being identified in numerous coral species, with prior research indicating that different cryptic genetic lineages can exhibit varied responses to environmental changes. This suggests a potential link between cryptic coral lineages and local environmental conditions. In this study, we investigate how communities of cryptic coral lineages vary along environmental gradients. We began by identifying cryptic genetic lineages within six coral species sampled around St. Croix, USVI based on 2b-RAD sequencing data. We then analyzed associations between the distributions of cryptic lineages across the six coral species (i.e., "cryptic coral community composition") and ecoregions, or geographically distinct environmental conditions. Our findings show that depth is a more significant predictor of community composition than ecoregions and is the most influential factor among the 40 abiotic variables that characterize ecoregions. These results imply that cryptic coral communities are influenced by both depth and local environmental conditions, although the exact environmental factors driving these patterns remain unknown. Understanding community turnover across a seascape is important to consider when outplanting corals to restore a reef, as locally-adapted lineages may have differential fitness in different environmental conditions.

Mid-Late Holocene coral calcification dynamics: deciphering climatic and environmental effects

Over the past four decades, a marked decrease in coral calcification has occurred across the world's tropical reefs, closely linked to climate change and the impact of human activity. However, how natural and human-induced factors influence coral calcification remains unclear due to limited understanding of the geological past. This study addresses this gap by investigating the calcification parameters of 82 Porites corals from the northern South China Sea, with growth periods covering distinct climatic epochs during the Mid-Late Holocene, including the Holocene Climate Optimum, 4.2 ka BP event, Medieval Climate Anomaly, Little Ice Age and Current Warm Period. Our findings show a gradual increase in coral skeletal density towards the present, and varied linear extension and calcification rates between warm and cold phases and between pre- and post-industrial periods. This suggests that temperature plays a pivotal role in controlling coral calcification, with contingent influences from volcanic activity and solar radiation. Notably, the linear extension and calcification rates were significantly reduced during the Current Warm Period, suggesting a surpassing impact of contemporary human activities over the natural variability on coral calcification. This raises concerns about the future prospects of coral reefs in the face of ongoing climate change and increasing impact of human activity.

Review of CO2 extraction from seawater through non-electrochemical and electrochemical approaches

As the most significant carbon sink on Earth, the ocean has been inevitably absorbing excess atmospheric CO2, leading to high concentration of CO2 that threatens marine life. Like emissions of greenhouse gases, this issue demands urgent attention. Hence, comprehensive investigation and comparison, including both non-electrochemical and electrochemical direct ocean capture (DOC) methods, are revealed in this review. The non-electrochemical approach utilizes specialized materials such as gas-permeable membranes (GPM), hollow fiber membrane contactors (HFMC), and ion exchange resins to extract CO2 from seawater. In contrast, the electrochemical method employs chemical reactions to generate H+ or OH- ions, which adjust the pH value of seawater to either release CO2 gas or precipitate carbonate, thereby removing dissolved carbon. This article comprehensively overviews each method, including the latest research findings, underlying principles, employed equipment, and performance metrics. Finally, the achievements, current gaps, corresponding perspectives, and potential solutions in CO2 capture from seawater are also proposed.

Mass Die-Off Events in Swarming Hyperiid Amphipods: Potential Drivers

Beach mass stranding events of marine organisms, widely documented worldwide, are triggered by a range of biotic and abiotic environmental factors, often unexplained. Such occurrences among pelagic crustaceans are less frequent, yet not uncommon. Here we studied mass mortality events of hyperiid amphipods-abundant members of pelagic zooplankton, commonly associated with gelatinous organisms. Our study examined consecutive mass die-off and stranding events of free-living hyperiids in the Red Sea during 2023 and 2024. We investigated three potential causes: semelparous reproduction, thermal stress, and physical oceanographic conditions. To place our findings in a broader context, we further performed a global review of hyperiid swarming and mass mortality events from scientific literature and a citizen science repository. Morphological and molecular analyses confirmed that the hyperiid species in the die-off events at the Red Sea was Anchylomera blossevillei (Phrosinidae). The balanced male: female sex ratio (0.99), combined with the absence of gravid or brooding females, led to the rejection of semelparity as a driving factor. The environmental data did not indicate thermally stressful conditions, and no evidence of parasitic infection was found. Nonetheless, previous studies have shown that under weak wind conditions, as measured during the stranding events, coherent cyclonic eddies with diameters of 5-6 km are developed in the northern Gulf of Aqaba, persisting for about a day. These eddies can exceed velocities of 100 cm s-1 and may have facilitated the hyperiid stranding events. Future research should unveil the impacts of such events on marine ecosystems.

Improving Carbon Budgets by Accounting for Inorganic Carbon in Seagrass Ecosystems

While seagrass ecosystems are acknowledged for their role as blue carbon sinks, significant uncertainties remain regarding the sequestration of sediment inorganic carbon (SIC) and its broader implications for carbon cycling. These knowledge gaps hinder a comprehensive assessment of the contribution of seagrass ecosystems to the global carbon budget. To address this gap, the drivers and sources of SIC in nine seagrass ecosystems in the tropical Indo-Pacific were analyzed using partial least squares path modeling and carbon and oxygen isotopes binding Bayesian mixing models. We found that SIC content varies regionally, ranging from 0.03% to 10.18%, and is positively correlated with seagrass biomass, temperature, salinity, and coarse-grained sediment. SIC stocks ranged from 1.53 to 203.17 Mg C ha-1, confirming the role of tropical Indo-Pacific seagrass ecosystems as a significant pool for SIC. SIC content and stock beneath seagrass ecosystems are generally higher than those in unvegetated areas due to the capacity to trap particles of the seagrass canopy. SIC beneath seagrass ecosystems affected by runoff is mainly from terrestrial inputs. Conversely, SIC under seagrass ecosystems regulated by seawater is primarily derived from local production and inputs from adjacent ecosystems and fish farming wastewater. This study provides a robust method to enhance the accuracy of blue carbon accounting in seagrass ecosystems by the inclusion of inorganic carbon burial.

Seatizen Atlas: a collaborative dataset of underwater and aerial marine imagery

Citizen Science initiatives have a worldwide impact on environmental research by providing data at a global scale and high resolution. Mapping marine biodiversity remains a key challenge to which citizen initiatives can contribute. Here we describe a dataset made of both underwater and aerial imagery collected in shallow tropical coastal areas by using various low cost platforms operated either by citizens or researchers. This dataset is regularly updated and contains >1.6 M images from the Southwest Indian Ocean. Most of images are geolocated, and some are annotated with 51 distinct classes (e.g. fauna, and habitats) to train AI models. The quality of these photos taken by action cameras along the trajectories of different platforms, is highly heterogeneous (due to varying speed, depth, turbidity, and perspectives) and well reflects the challenges of underwater image recognition. Data discovery and access rely on DOI assignment while data interoperability and reuse is ensured by complying with widely used community standards. The open-source data workflow is provided to ease contributions from anyone collecting pictures.

An African perspective to biodiversity conservation in the twenty-first century

Africa boasts high biodiversity while also being home to some of the largest and fastest-growing human populations. Although the current environmental footprint of Africa is low compared to other continents, the population of Africa is estimated at around 1.5 billion inhabitants, representing nearly 18% of the world's total population. Consequently, Africa's rich biodiversity is under threat, yet only 19% of the landscape and 17% of the seascape are under any form of protection. To effectively address this issue and align with the Convention on Biological Diversity's ambitious '30 by 30' goal, which seeks to protect 30% of the world's land and oceans by 2030, substantial funding and conservation measures are urgently required. In response to this critical challenge, as scientists and conservationists working in Africa, we propose five recommendations for future directions aimed at enhancing biodiversity conservation for the betterment of African society: (i) accelerate data collection, data sharing and analytics for informed policy and decision-making; (ii) innovate education and capacity building for future generations; (iii) enhance and expand protected areas, ecological networks and foundational legal frameworks; (iv) unlock creative funding channels for cutting-edge conservation initiatives; and (v) integrate indigenous and local knowledge into forward-thinking conservation strategies. By implementing these recommendations, we believe Africa can make significant strides towards preserving its unique biodiversity, while fostering a healthier society, and contributing to global conservation efforts.This article is part of the discussion meeting issue 'Bending the curve towards nature recovery: building on Georgina Mace's legacy for a biodiverse future'.

Drivers of spatiotemporal variability in a marine foundation species

Marine foundation species are critical for the structure and functioning of ecosystems and constitute the pillar of trophic chains while also providing a variety of ecosystem services. In recent decades, many foundation species have declined in abundance, sometimes threatening their current geographical distribution. Kelps (Laminariales) are the primary foundation species in temperate coastal systems worldwide. Kelp ecosystems are notoriously variable, challenging the identification of key factors controlling their dynamics. Identification of these drivers is key to predicting the fate of kelp ecosystems under climatic change and to informing management and conservation decisions such as restoration. Here, we used in situ data from long-term monitoring programs across 1350 km of coast spanning multiple biogeographic regions in the state of California (USA) to identify the major regional drivers of density of two dominant canopy-forming kelp species and to elucidate the spatial and temporal scales over which they operate. We used generalized additive mixed models to identify the key drivers of density of two dominant kelp species (Nereocystis luetkeana and Macrocystis pyrifera) across four ecological regions of the state of California (north, central, southwest, and southeast) and for the past two decades (2004-2021). The dominant drivers of kelp density varied among regions and species but always included some combination of nitrate availability, wave energy and exposure, density of purple sea urchins, and temperature as the most important predictors. These variables explained 63% of the variability of bull kelp in the northern and central regions, and 45% and 51.4% of the variability in giant kelp for the central/southwest and southeast regions, respectively. These large-scale analyses infer that a combination of lower nutrient availability, changes in wave energy and exposure, and increases in temperature and purple sea urchin counts have contributed to the decline of kelp observed in the last decade. Understanding the drivers of kelp dynamics can be used to identify regional patterns of historical stability and periods of significant change, ultimately informing resource management and conservation decisions such as site selection for kelp protection and restoration.

Metabolic complexities and heterogeneity in quorum sensing signaling molecules in bacteria isolated from black band disease in a Caribbean coral

Coral diseases contribute to the worldwide loss of coral reefs, with the Black Band Disease (BBD) being a prominent example. BBD is an infectious condition with lesions with a pigmented mat composed of cyanobacteria, sulphate-reducing, sulphide-oxidizing, and heterotrophic bacteria. We compared the heterotrophic bacterial communities of healthy and BBD-affected colonies of the Caribbean coral Orbicella faveolata using culture-dependent and -independent techniques. Twenty and 23 bacterial isolates were identified from healthy and diseased tissues, respectively, which differed in their capacities to metabolize carbohydrates and citrate, either anaerobically or aerobically. They also differed in their quorum-sensing (QS) activity, as QS signaling molecules were found exclusively, and QS-inhibition was found primarily, in isolates from diseased tissues. Screening of bacterial diversity by 16SrDNA metabarcoding showed that members of the bacterial genera Muricauda and Maritimimonas were dominant in healthy tissues whereas members of the cyanobacterial genus Roseofilum were dominant in diseased tissues. These results suggest that bacterial dysbiosis can be linked with altered bacterial communication, likely leading to diachrony and imbalance that may participate in the progression of BBD. Investigating physiological traits and QS-based communication offers insights into the onset and progression of coral infections, paving the way for novel strategies to mitigate their impact.

Extreme Environmental Variability Induces Frontloading of Coral Biomineralisation Genes to Maintain Calcification Under pCO2 Variability

Corals residing in habitats that experience high-frequency seawater pCO2 variability may possess an enhanced capacity to cope with ocean acidification, yet we lack a clear understanding of the molecular toolkit enabling acclimatisation to environmental extremes or how life-long exposure to pCO2 variability influences biomineralisation. Here, we examined the gene expression responses and micro-skeletal characteristics of Pocillopora damicornis originating from the reef flat and reef slope of Heron Island, southern Great Barrier Reef. The reef flat and reef slope had similar mean seawater pCO2, but the reef flat experienced twice the mean daily pCO2 amplitude (range of 797 v. 399 μatm day-1, respectively). A controlled mesocosm experiment was conducted over 8 weeks, exposing P. damicornis from the reef slope and reef flat to stable (218 ± 9) or variable (911 ± 31) diel pCO2 fluctuations (μatm; mean ± SE). At the end of the exposure, P. damicornis originating from the reef flat demonstrated frontloading of 25% of the expressed genes regardless of treatment conditions, suggesting constitutive upregulation. This included higher expression of critical biomineralisation-related genes such as carbonic anhydrases, skeletal organic matrix proteins, and bicarbonate transporters. The observed frontloading corresponded with a 40% increase of the fastest deposited areas of the skeleton in reef flat corals grown under non-native, stable pCO2 conditions compared to reef slope conspecifics, suggesting a compensatory response that stems from acclimatisation to environmental extremes and/or relief from stressful pCO2 fluctuations. Under escalating ocean warming and acidification, corals acclimated to environmental variability warrant focused investigation and represent ideal candidates for active interventions to build reef resilience while societies adopt strict policies to limit climate change.

Effects of Environmental and Climatic Changes on Coral Reef Islands

Coral reef islands are low-lying, wave-deposited sedimentary landforms. Using an eco-morphodynamic framework, this review examines the sensitivity of islands to climatic and environmental change. Reef island formation and morphological dynamics are directly controlled by nearshore wave processes and ecologically mediated sediment supply. The review highlights that reef islands are intrinsically dynamic landforms, able to adjust their morphology (size, shape, and location) on reef surfaces in response to changes in these processes. A suite of ecological and oceanographic processes also indirectly impact hydrodynamic and sediment processes and thereby regulate morphological change, though the temporal scales and magnitudes of impacts on islands vary, leading to divergent morphodynamic outcomes. Climatic change will modify the direct and indirect processes, causing complex positive and negative outcomes on islands. Understanding this complexity is critical to improve predictive capabilities for island physical change and resolve the timescales of change and lag times for impacts to be expressed in island systems.

Ecology of endolithic bryozoans: colony development, growth rates and interactions of species in the genus Immergentia

Boring bryozoans dissolve calcium carbonate substrates, leaving unique borehole traces. Depending on the shell type, borehole apertures and colony morphology can be diagnostic for distinguishing taxa, but to discriminate among species their combination with zooidal morphology is essential. All boring (endolithic) bryozoans are ctenostomes that, along with other boring taxa, are common in benthic communities. The growth rates of such bryozoans, including Immergentiidae, are largely unknown. For the first time laboratory experiments were conducted to determine growth rates and early colony development of the intertidal species Immergentia stephanieae and the subtidal species I. cf. suecica from Roscoff, France. In growth experiment 1, ancestrular growth rates varied, with the highest rates in I. stephanieae at 96.5 µm day-1 and the lowest at 1.1 µm day-1, during the period of August to October, in which the number of reproductive zooids was comparably higher than in other months of the year. Immergentia cf. suecica had a higher proportion of reproductive zooids from December to March compared to other months. In growth experiment 2, the bryozoans were fed a culture mixture of Chaetoceros calcitrans and Tisochrysis lutea which was compared with a control. The growth rate of small colonies of comparable size was greater in the food-enriched samples compared to the control (non-enriched). In larger colonies, the trend differed with greater growth (cystid appendage expansion) rate reported for some samples in the control. In food-enriched samples ancestrulae of I. stephanieae grew at 23 µm day-1 and I. cf. suecica 9.3 µm day-1 while no growth was observed in the control of I. cf. suecica, but 0.4 µm day-1 was reported for I. stephanieae. Growth patterns in the early developmental stages showed that the budding patterns from the ancestrulae were the same for both species, with different enantiomorphic tendencies. Inter- and intraspecific interactions are also discussed. The distribution of immergentiids is presented, as are records from new locations and the greatest subtidal depth of collection reported to date.

Diversity and future perspectives of Mediterranean deep-water oyster reefs

Anthropogenic and climate factors are increasingly affecting the composition and functions of many marine biogenic reefs globally, leading to a decline in associated biodiversity and ecosystem services. Once dominant ecological component, modern oyster reefs in the Mediterranean and Black Sea and the Atlantic Ocean have already been profoundly altered by overharvesting, habitat loss and the introduction of alien species. Far less known are deep-water oyster reefs, which can however form substantial biogenic structures below 30 m depth. Here we analyze the diversity of benthic assemblages associated with deep-water oyster reefs formed by the gryphaeid Neopycnodonte cochlear, and other mesophotic habitats in the central Mediterranean Sea using a taxonomic and functional approach. Our findings suggest that deep-water oyster reefs may act as hotspots of biodiversity and ecological functions in the Mediterranean Sea under current conditions, having also an edge in survival in a changing ocean.

Efficacy of the 28S rDNA barcode in differentiating Caribbean octocorals

The ecological landscape of Caribbean reefs is rapidly changing as octocorals fill the void left by declining scleractinian populations. Effective molecular barcodes are necessary to accurately identify these octocorals and monitor this shifting ecosystem. We tested the efficacy of the 28S rDNA as a barcode compared to the most commonly used mtMutS barcode on a collection of octocorals from across the Caribbean. Based on pairwise genetic distance values, 28S appeared to be more effective at differentiating species within the families Plexauridae and Gorgoniidae, while mtMutS was slightly more effective at distinguishing species of Pterogorgiidae. However, the standard 28S rDNA primers did not amplify all species as effectively as mtMutS, especially those belonging to the genus Eunicea. A shorter 28S barcode developed for eDNA applications distinguished species as effectively as the complete 28S barcode.

Coral reef rehabilitation following Hurricane Irma using nano-engineered artificial reefs in Sint Maarten

Artificial reefs are being increasingly deployed as a coral reef restoration strategy. Additional reef habitats made from conventional substrates (e.g., metal, concrete, etc.) have had limited success in addressing conservation objectives on degraded coral reefs due to structure size and lack of standardized monitoring, and inability to enhance select ecological, and species variables. Technological advances and new restoration methods must be quickly tested and applied on a large scale to curb further deterioration of coral reefs. Here, we present the results of the first deployment of Oceanite artificial reefs (ARs). We compare the composition of the benthic community and associated fish assemblages on Oceanite ARs 14 months after deployment in a marine protected area (MPA) and two unprotected sites in Philipsburg, Sint Maarten. We also examined fish abundance and behaviour on the ARs. The initial results from this pilot study suggest that Oceanite mineral matrices can enhance local biodiversity, attract coral recruits, provide food and protection for large fish communities, and develop an early stage, healthy coral reef community in 14 months. We suggest that further research and testing of Oceanite capabilities will allow us to develop site-, species-, and function-specific nanotechnology-enabled substrates to optimize AR conservation goals. Oceanite mix designs can be tuned to precise parameters to promote reef restoration and stressor mitigation (e.g., pH, leachate emissions, surface texture, porosity, void structure, and hydrophobic, heat-absorbing, and disease-fighting properties). Using both bottom-up and top-down restoration processes, we suggest that deploying bio-enhancing habitats with targeted microclimate stressor treatments on the world's critical reefs will allow to build global refuges resilient to climate change and provide much needed ecosystem services.

Principle Design of C-C Coupling Pathway Towards Highly Selective C2 Products Using Photocatalytic CO2 Reduction:A Review

Photocatalytic conversion of environmental CO2 into valuable fuels is expected to alleviate fossil fuel and pollution problems. However, intricate product-reaction pathways complicate the regulation of product selectivity. Most studies in this field have focused on increasing productivity rather than on controlling product formation. To date, the major products of photocatalytic CO2 reduction reactions (CO2RRs) are C1 compounds, as opposed to the higher-value C2 compounds, because of the low C2 selectivity of this process. The design of C-C coupled pathways is paramount to facilitate selective access to C2 products in the photocatalytic CO2RR. In this review, we discuss the mechanisms and pathways of CO2RR product generation based on recent research results and summarise the work on CO2RR to C2 products. This review aims to modulate the product-generation pathway to improve the yield and selectivity of C2 products by facilitating C-C coupling reactions. Finally, some of the current challenges in the field of the CO2RR to C2 are outlined, including possible mechanistic interpretations, cost of catalyst use, reactor design, and potential solutions.

Climate change undermines seafood micronutrient supply from wild-capture fisheries in Southeast Asia and Pacific Island countries

Marine ecosystem functions are affected by climate change impacts such as ocean warming, deoxygenation and acidification. These impacts drive changes in distributions and body size of fish species and directly affect fisheries. Wild-capture fisheries are crucial for providing nutrients, livelihoods, and employment in tropical Southeast Asia and Pacific Island countries, where coastal communities are highly vulnerable to climate change. We examined the impacts of climate change on fish stocks and nutrient availability of seven key micronutrients (calcium, Omega-3 fatty acids, iodine, iron, vitamin A, vitamin B12 and zinc) in Southeast Asia, Pacific Islands, and Oceania (Australia and New Zealand). We combined micronutrient demands by local human populations with Sea Around Us reconstructed catch time series and catch projections from a dynamic bioclimate envelope model for the 21st century. The model predicted a decline in the Maximum Catch Potential (MCP) within Exclusive Economic Zones for Oceania, Pacific Islands, and Southeast Asian countries. Under the 'strong mitigation' scenario, catch potential reductions ranged from a decline of 54-66 % in Oceania, 58-92 % in Pacific Islands, and 65-86 % in Southeast Asia by the mid to the end of the 21st century relative to the historical period, respectively. Under the 'no-mitigation' climate scenario, reductions were more severe, with a decline of 55-70 % in Oceania, 66-92 % in Pacific Islands, and 70-86 % in Southeast Asia for the same time periods. Our findings indicate that Australia and New Zealand are unlikely to meet the recommended nutrient intake demand for most micronutrients through their fisheries (not considering trade or aquaculture production), except for iodine and vitamin B12. Pacific Island countries will likely follow the same pattern while Southeast Asia is expected to face worsening deficits, except for iodine and vitamin B12. This study highlights the importance of incorporating nutritional considerations of seafood into national food, trade and economic policies.

Interspecies differences in the transcriptome response of corals to acute heat stress

Rising sea surface temperatures threaten the survival of corals worldwide, with coral bleaching events becoming more commonplace. However, different coral species are known to exhibit variable levels of susceptibility to thermal stress. To elucidate genetic mechanisms that may underlie these differences, we compared the gene repertoire of four coral species, Favites colemani, Montipora digitata, Acropora digitifera, and Seriatopora caliendrum, that were previously demonstrated to have differing responses to acute thermal stress. We found that more tolerant species, like F. colemani and M. digitata, possess a greater abundance of antioxidant protein families and chaperones. Under acute thermal stress conditions, only S. caliendrum showed a significant bleaching response, which was accompanied by activation of the DNA damage response network and drastic upregulation of stress response genes (SRGs). This suggests that differences in SRG orthologs, as well as the mechanisms that control SRG expression response, contribute to the ability of corals to maintain stability of physiological functions required to survive shifts in seawater temperature.

Abundance of microplastics and its ecological risk assessment in coral reef regions of Peninsular Malaysia

Microplastic contamination is an emerging concern in marine ecosystems, with limited knowledge on its impact on coral reefs, particularly in Malaysia. Surface waters were collected from several coral reef regions in Peninsular Malaysia by towing a plankton net behind the boat. Microplastics were detected at all sites, with a mean abundance of 0.344 ± 0.457 MP/m3. Perhentian Islands (0.683 ± 0.647 MP/m3) had significantly higher microplastic levels than Tioman Island (0.108 ± 0.063 MP/m3), likely due to oceanographic differences. Over half of the microplastics (55.7 %) were small microplastics (<1 mm), with the 0.05-0.5 mm size class being most abundant (29.2 %). Fragments and fibres dominated, and black, blue, and green were the prevalent colours. Polyethylene (PE), rayon (RY), chlorinated polyethylene (CPE), and polypropylene (PP) were the most common polymers. This study reveals the abundance and characteristics of microplastics, provides important data for further research on microplastics in coral reef ecosystem.

Coastal water quality improves during the COVID-19 pandemic: Maui, Hawai'i

Coastal ecosystems are increasingly threatened by degraded water quality linked to agriculture, wastewater and changes in land-use. This study collected coastal water quality measurements to assess spatiotemporal trends and drivers of variability on the island of Maui, Hawai'i. We also utilized Hawai'i's COVID-19 visitor quarantine, which dropped visitor numbers on Maui by >99 %, to evaluate the effects of population on coastal water quality. Nitrate and turbidity were highest on the north shore and during the winter. This trend is likely driven by a combination of fertilizers associated with agriculture and nearby wastewater injection wells, and large swells, respectively. All sites exceeded the State's water quality standard (WQS) for turbidity, and many sites exceed the WQS for nitrate. During the COVID-19 pandemic, coastal water quality improved across many sites, which is likely related to the visitor population reduction and stay-at-home orders that resulted in limited use of beaches and roads.

Seascape Genomics of the Smooth Hammerhead Shark Sphyrna zygaena Reveals Regional Adaptive Clinal Variation

Globally, hammerhead sharks have experienced severe declines owing to continued overexploitation and anthropogenic change. The smooth hammerhead shark Sphyrna zygaena remains understudied compared to other members of the family Sphyrnidae. Despite its vulnerable status, a comprehensive understanding of its genetic landscape remains lacking in many regions worldwide. The present study aimed to conduct a fine-scale genomic assessment of Sphyrna zygaena within the highly dynamic marine environment of South Africa's coastline, using thousands of single nucleotide polymorphisms (SNPs) derived from restriction site-associated DNA sequencing (3RAD). A combination of differentiation-based outlier detection methods and genotype-environment association (GEA) analysis was employed in Sphyrna zygaena. Subsequent assessments of putatively adaptive loci revealed a distinctive south to east genetic cline. Among these, notable correlations between adaptive variation and sea-surface dissolved oxygen and salinity were evident. Conversely, analysis of 111,243 neutral SNP markers revealed a lack of regional population differentiation, a finding that remained consistent across various analytical approaches. These results provide evidence for the presence of differential selection pressures within a limited spatial range, despite high gene flow implied by the selectively neutral dataset. This study offers notable insights regarding the potential impacts of genomic variation in response to fluctuating environmental conditions in the circumglobally distributed Sphyrna zygaena.

Scleractinian Corals at Their Subtropical Southwestern Atlantic Limit: Post‐2019 Mass Bleaching Event Analysis

Thermal anomalies caused by climate change have emerged as a major threat to reef ecosystems globally. While the effects of warming oceans have been extensively investigated in tropical reefs, its effects on subtropical reefs, where coral diversity is lower, remain largely unstudied. We analysed the spatial distribution, mean cover and health status of scleractinian corals in the subtropical rocky reefs of the Alcatrazes Archipelago, a no‐take marine protected area located 30 km off the coast of São Paulo state, Brazil (24° S). Data were collected before (2018) and after (2022) the most intense marine heatwave ever recorded in the region, in 2019, using either fixed or random photoquadrats. Five scleractinian corals were recorded as follows: The zooxanthellate massive species Mussismilia hispida and Madracis decactis, the azooxanthellate solitary corals Astrangia spp. and Coenocyathus sebroecki and the invasive sun coral Tubastraea spp. M. hispida and M. decactis were the most abundant species, particularly in the sheltered sites, while Astrangia spp. and C. sebroecki were less abundant and only recorded in the exposed side of the island. In the single site where Tubastraea spp. colonies prevailed, other coral species were nearly absent. Both M. hispida and M. decactis exhibited resilience to the 2019's bleaching event, with their abundance remaining almost the same in 2022. Our findings add evidences to the emerging idea that subtropical reefs in the southwestern Atlantic may serve as refuges during future thermal anomalies, highlighting the importance of monitoring these reefs in the context of changing habitats driven by warming oceans.

The Loss of Beneficial Thermal Priming on Global Coral Reefs

Warm-season marine heatwaves (MHWs) have greatly increased in frequency, severity, and extent over the last few decades, driving more frequent and severe coral bleaching episodes. Given the grave near-term threat to coral reefs imposed by MHWs, it is important to assess the mechanisms by which corals may acquire higher thermal tolerance. Recent field and laboratory studies have demonstrated that exposure to sublethal heat stress, known as "priming," can reduce bleaching susceptibility during a subsequent MHW. Little is known, however, about how often priming conditions occur, and how effective those conditions may be at protecting coral reefs. We employed a global historical coral bleaching database and a high-resolution sea surface temperature dataset to assess the frequency of priming and examine its effect on coral bleaching sensitivity on a global scale. The analysis showed that coral reefs in parts of the western to central tropical Pacific experienced priming on average over twice a decade and had a higher likelihood of priming protection. Mixed-effects regression models indicated that priming conditions could mitigate coral bleaching response by up to 12% in advance of a moderate MHW. However, the protective effect of priming decreased, and even became harmful, with more severe MHWs. We detected spatial variations in priming frequency that could provide insight for conservation planning and explain some variations in bleaching sensitivity to MHWs. Even so, our findings suggest that thermal priming will not be sufficient to protect most coral reefs from MHWs in the future, without substantial efforts to mitigate climate change.

Inter- and intraspecific responses of coral colonies to thermal anomalies on Palmyra Atoll, central Pacific

Long-term monitoring of individual coral colonies is important for understanding variability between and within species over time in the context of thermal stress. Here, we analyze an 11-year time series of permanent benthic photoquadrats taken on Palmyra Atoll, central Pacific, from 2009 to 2019 to track the growth (i.e., increase in live planar area), pigmentation or lack thereof ("discoloration"), partial or whole-colony mortality, survival, and regrowth of 314 individual coral colonies of nine focal species from two reef habitat types. During this period, thermal anomalies occurred on Palmyra in conjunction with El Niño-Southern Oscillation events in both 2009 and 2015, of which the latter heatwave was longer-lasting and more thermally-severe. We found that coral responses varied by habitat, within and among species, and/or according to the degree of accumulated thermal stress. Nearly all species, particularly Stylophora pistillata and Pocillopora damicornis, responded more negatively to the 2015 heatwave in terms of colony-specific discoloration and reduction in live planar area. While discoloration was more prominent at the shallower reef terrace compared to the fore reef for this subset of colonies, the reef terrace exhibited greater stability of community-wide coral cover. Colony fate was associated with severity of discoloration at the time of warming: one year following the 2009 heatwave, more severely discolored colonies were more likely to grow, yet following the second heatwave in 2015, colonies were more likely to experience shrinkage or mortality. However, colonies that were more severely discolored in 2009 were not necessarily more discolored in 2015, suggesting that colony-specific factors may be more influential in governing responses to thermal stress.

Optical Flow Sensor with Fluorescent-Conjugated Hyperelastic Pillar: A Biomimetic Approach

Although the Doppler velocity log is widely applied to measure underwater fluid flow, it requires high power and is inappropriate for measuring low flow velocity. This study proposes a fluid flow sensor that utilizes optical flow sensing. The proposed sensor mimics the neuromast of a fish by attaching a phosphor to two pillar structures (A and B) produced using ethylene propylene diene monomer rubber. The optical signal emitted by the phosphor is measured using a camera. An experiment was conducted to apply an external force to the reactive part using a push-pull force gauge sensor to confirm the performance of the proposed sensor. The optical signal emitted by the phosphor was obtained using an image sensor, and a quantitative value was calculated using image analysis. A simulation environment was constructed to analyze the flow field and derive the relationship between the flow rate and velocity. The physical properties of the pillar were derived from hysteresis measurement results, and the error was minimized when pillar types A and B were utilized within the ranges of 0-0.1 N and 0-2 N, respectively. A difference in the elastic recovery characteristics was observed; this difference was linear based on the shape of the pillar, and improvement rates of 99.585% and 99.825% were achieved for types A and B, respectively. The proposed sensor can help obtain important information, such as precise flow velocity measurements in the near field, to precisely navigate underwater unmanned undersea vehicles and precisely control underwater robots after applying the technology to the surface of various underwater systems.

Saving coral reefs: significance and biotechnological approaches for coral conservation

Coral reefs are highly productive ecosystems that provide valuable services to coastal communities worldwide. However, both local and global anthropogenic stressors, threaten the coral-algal symbiosis that enables reef formation. This breakdown of the symbiotic relationship, known as bleaching, is often triggered by cumulative cell damage. UV and heat stress are commonly implicated in bleaching, but other anthropogenic factors may also play a role. To address coral loss, active restoration is already underway in many critical regions. Additionally, coral researchers are exploring assisted evolution methods for greater coral resilience to projected climate change. This review provides an overview of the symbiotic relationship, the mechanisms underlying coral bleaching in response to stressors, and the strategies being pursued to address coral loss. Despite the necessity of ongoing research in all aspects of this field, action on global climate change remains crucial for the long-term survival of coral reefs.

Experimental coral reef communities transform yet persist under mitigated future ocean warming and acidification

Coral reefs are among the most sensitive ecosystems affected by ocean warming and acidification, and are predicted to collapse over the next few decades. Reefs are predicted to shift from net accreting calcifier-dominated systems with exceptionally high biodiversity to net eroding algal-dominated systems with dramatically reduced biodiversity. Here, we present a two-year experimental study examining the responses of entire mesocosm coral reef communities to warming (+2 °C), acidification (-0.2 pH units), and combined future ocean (+2 °C, -0.2 pH) treatments. Contrary to modeled projections, we show that under future ocean conditions, these communities shift structure and composition yet persist as novel calcifying ecosystems with high biodiversity. Our results suggest that if climate change is limited to Paris Climate Agreement targets, coral reefs could persist in an altered state rather than collapse.

Comparative analysis of biofilm bacterial communities developed on different artificial reef materials

AIMS

Artificial reefs play a vital role in restoring and creating new habitats for marine species by providing suitable substrates, especially in areas where natural substrates have been degraded or lost due to declining water quality, destructive fishing practices, and coral diseases. Artificial reef restoration aimed at coral larval settlement is gaining prominence and initially depends on the development of biofilms on reef surfaces. In this study, we hypothesized that different artificial reef materials selectively influence the composition of biofilm bacterial communities, which in turn affected coral larval settlement and the overall success of coral rehabilitation efforts. To test this hypothesis, we evaluated the impact of six different reef-made materials (porcelain, granite, coral skeleton, calcium carbonate, shell cement, and cement) on the development of biofilm bacterial communities and their potential to support coral larval settlement.

METHODS AND RESULTS

The biofilm bacterial communities were developed on different artificial reef materials and studied using 16S rRNA gene amplicon sequencing and analysis. The bacterial species richness and evenness were significantly (P < 0.05) low in the seawater, while these values were high in the reef materials. At the phylum level, the biofilm bacterial composition of all materials and seawater was majorly composed of Pseudomonadota, Cyanobacteria, and Bacteroidetes; however, significantly (P < 0.05) low Bacteroidetes were found in the seawater. At the genus level, Thalassomonas, Glaciecola, Halomicronema, Lewinella, Hyphomonas, Thalassospira, Polaribacter, and Tenacibaculum were significantly (P < 0.05) low in the coral skeleton and seawater, compared to the other reef materials. The genera Pseudoaltermonas and Thalassomonas (considered potential inducers of coral larval settlement) were highly abundant in the shell-cement biofilm, while low values were found in the biofilm of the other materials.

CONCLUSION

The biofilm bacterial community composition can be selective for different substrate materials, such as shell cement exhibited higher abundances of bacteria known to facilitate coral larval settlement, highlighting their potential in enhancing restoration outcomes.