Coral Reefs

The rariphotic zone, typically spanning depths of approximately 130 to 300 meters, represents a key transition between light-dependent coral reef ecosystems and the aphotic deep sea. Despite its potential ecological importance, including its proposed role as a refuge for species exposed to climate-driven stress, rariphotic ecosystems remain poorly understood. In this study, we conducted a systematic review and synthesis of the scientific literature on these habitats from 1970 to 2025. Following the PRISMA 2020 protocol, we analyzed 185 studies to characterize the historical development of research, identify geographic and methodological biases, and assess shifts in research priorities over five decades.Our results show a marked increase in research effort over the last decade, driven in part by advances in underwater technologies such as Remotely Operated Vehicles (ROVs), Human Occupied Vehicles (HOVs), and Baited Remote Underwater Video Station (BRUVS). However, this growth remains uneven, with persistent biases toward benthic rather than pelagic studies and a strong concentration of research in geographically accessible regions. Multivariate analyses of research novelty indicate that technological innovation and the formal recognition of the rariphotic zone in 2018 corresponded with major structural shifts in literature. Although the rariphotic zone is now increasingly recognized as an ecologically distinct component of the reef continuum, it remains underrepresented in ecological theory and conservation frameworks. Future research should move beyond descriptive taxonomic mapping toward integrative, data-driven functional ecology, with particular emphasis on long-term monitoring and depth-stratified connectivity.

Although corals are highly regenerative, some colonies in reef ecosystems completely recover from sublethal damage while other colonies exhibit partial mortality to similar injuries. To understand factors that might naturally curtail regenerative ability, we experimentally wounded small colonies in three coral genera (Acropora, Pocillopora, Porites) by mimicking natural corallivory using scraping (tissue and skeletal damage) or airbrushing (deep tissue removal with no skeletal injury). We found all scraped wounds regenerated rapidly in Acropora and Porites, while Pocillopora fragments frequently retained open lesions. In stark contrast, airbrushing resulted in algal colonization and delayed tissue healing and regeneration across all corals. Detailed cellular analysis of Porites wounds revealed two general phases comprising tissue regeneration: a healing phase defined by rapid coverage of bare skeleton with coenosarc, pigment cells and gastrodermal reformation, and then a second phase lasting one week ending in polyp regeneration. Red fluorescence appeared transiently in scrape wounds but persisted in tissue at the wound margin surrounding algae in airbrush wounds, suggesting that algal occupation of the wound bed inhibits coenosarc healing. Lastly, histological cross-sections of healing airbrush wounds in Porites revealed progressive loss of deep tissue leading to skeletal breakdown beneath the wound. Together, our results demonstrate the biphasic nature of tissue regeneration in colonial corals and provide a framework for understanding how biotic factors impact tissue repair and regeneration in nature.

Shifts from coral-dominated to macroalgal-dominated reef systems have become increasingly common in many coastal regions worldwide. Coral-macroalgal interactions have been shown to be generally detrimental to coral health, with macroalgal allelopathic compounds able to exert serious and even lethal effects on coral at various stages of growth and development. Previous studies have shown that the coral-associated microbial communities play important roles in coral health and mitigating external environmental stress, including macroalgal contact stress. However, it remains unclear whether changes in the coral microbiome have an influence on the Symbiodiniaceae community composition, and if such changes subsequently affect coral health. In this study, we examined changes in both the coral microbiome and the Symbiodiniaceae communities of two Singaporean coral species (Pocillopora acuta and Merulina ampliata) when exposed to both direct and water-mediated macroalgal contact with Lobophora sp. This was investigated using 16S rRNA gene amplicon sequencing to characterize the coral microbiome, and ITS2 variable region sequencing to profile the Symbiodiniaceae communities. Although no significant differences were observed for the coral microbiomes and Symbiodiniaceae communities at both alpha-and beta- diversity levels between control and macroalgal contact treated fragments within each coral species, inter-colony variations in responses to macroalgal contact were observed for both the coral microbiome and Symbiodiniaceae communities of M. ampliata. These results suggest that coral colonies vary in the mechanisms that allow mitigation of the effects of macroalgal contact, and in their resilience to macroalgal-induced stress.

Rising ocean temperatures disrupt previously stable coral-microbe interactions, leading to widespread coral mortality and threatening reef ecosystems worldwide. Growing evidence demonstrates the coral microbiome, including protists, plays a critical role in the host response to thermal stress. Specifically, corallicolids (Phylum: Apicomplexa) are positively correlated with thermal stress mortality in soft corals. This study investigates changes in the eukaryotic microbiome of the stony coral, Pocillopora damicornis, across an experimental thermal stress event. Using anti-metazoan 18S rRNA gene metabarcoding, protist communities were assessed at four time-points during experimental thermal stress. Outside of the Symbiodiniaceae, a prominent shift in microbiome composition during thermal stress was observed, most notably a significant increase and dominance in Corallicolida abundance in heat-stressed corals, while other protists declined substantially. Increased corallicolid abundance concurrent with bleaching suggests an overlooked compounding stressor beyond the loss of algal symbionts during heat stress. These results contrast with previous research on Pocillopora microbiomes showing prokaryotic community stability throughout stress, and support the hypothesis that thermal stress may alter the coral-corallicolid relationship, potentially shifting corallicolids from a commensal to a parasitic role, and synergistically contributing to coral mortality during and after heat stress. This work provides critical insight into the role of protists in marine holobionts, supports their inclusion in future microbiome studies, and informs strategies to improve coral resilience under climate change.

The global coral reef crisis has prompted restoration initiatives worldwide. Targeting the coral larval stage is among the most scalable approaches as recruitment operates over large spatial scales. It thus represents one of the best levers for coral population recovery. Active coral larval seeding has shown considerable success, and passive substrate engineering has emerged as a promising complementary strategy. Coral settlement modules featuring helix recesses have increased settlement and survival by up to 80-fold on small experimental units, but whether these results translate to tools deployable at the scale of thousands of units, remains yet an open question. Here, we transferred structural features from successful experimental coral settlement designs into production-ready concrete modules to (i) evaluate coral recruitment on five designs at four reef sites differing in flow regime and coral cover over one year; (ii) compare production-scale performance against experimental clay modules and natural reef substrate; and (iii) identify key parameters for large-scale production. The helix recess geometry of coral settlement modules outperformed the featureless control design approximately 20-fold and exceeded natural reef recruitment at least 3- to 32-fold. The helix features were successfully transferred from experimental clay to production-scale concrete modules, yielding comparable settlement densities when standardized to crevice length, which proved to be the biologically relevant unit of available habitat. Production feasibility was demonstrated by producing 690 modules for deployment on a hybrid reef on the west side of Oahu, Hawaii. The passive coral larval recruitment approach presented here could substantially improve the logistical and economic feasibility of large-scale coral reef restoration. This approach requires neither coral larval rearing, handling, nor coral fragmenting, and is compatible with active larval seeding where genetic diversity or larvae supply are limiting factors. The coral settlement modules can be cast in standardized concrete molds at precast facilities. Modules have demonstrated consistent coral recruitment enhancement across reef environments with contrasting flow and coral cover. Deploying mixed arrays of helix-recess structures with designs offering multi-level complexity and three-dimensional rugosity maximizes outcomes for coral, fish, and invertebrate communities simultaneously. Site selection is the most critical deployment decision and should consider larval supply, hydrodynamics, and substrate stability which drive recruitment outcomes more than design choice alone. The modules offer a range of application potential, ranging from integration into existing coastal infrastructure over stand-alone reef restoration approaches, to substrate-consolidating interconnected arrangements.

Local and global stressors are driving declines in competitive reef-building corals and favouring stress-tolerant, weedy species. In many of these taxa, rapid asexual reproductive strategies promote the proliferation of existing genotypes at small spatial scales, potentially leading to the formation of monospecific stands ("carpets"). Such reproductive strategies raise concerns for the intraspecific diversity and resilience of future reefs. The genetic structure of these spatially dominant, weedy corals remains poorly understood, in part because densely aggregated colonies lack distinct boundaries, hindering the use of standard sampling designs. We employed a photogrammetry-guided, spatially explicit sampling approach to assess the genotypic diversity and genet distribution in the increasingly dominant scleractinian coral Madracis auretenra across three reef sites in Curacao. Cover of M. auretenra varied widely among sites and reef zones (4.1-26.2%). Genome-wide genotyping of 678 samples collected at 1-m intervals identified two genetically distinct lineages comprising 90% and 10% of the samples, with contrasting genotypic diversity (genet-to-ramet ratio Ng/N = 0.287 and 0.481, respectively). Monospecific stands (n = 20) usually contained multiple genotypes and occasionally even both lineages, but were typically dominated by a single genotype (mean 65.5%, minimum 42.3%). Simulated sampling demonstrated that combining monostands, patches, and isolated colonies would maximise captured genotypic diversity for restoration applications. Our results demonstrate that photogrammetry-guided sampling provides an effective, unbiased framework for population-genetic studies of monostand-forming corals, while revealing substantial genotypic diversity within a species that is becoming increasingly dominant on southern Caribbean reefs.

Coral reefs are declining globally, creating an urgent need for scalable technologies that improve the efficiency and effectiveness of active reef restoration. Coral reef restoration is increasingly constrained by algal overgrowth, which suppresses coral growth, survival, and restoration efficiency. Building on the recently developed Coral Guard platform, we evaluate its restoration performance under long-term in situ coral nursery conditions and introduce Fusion Guard Tiles, a geometry-optimized Coral Guard design that accelerates microfragment fusion. We evaluated Coral Guard Plugs using the branching coral Stylophora pistillata under complementary ex situ conditions and Fusion Guard Tiles using the massive reef-building coral Porites evermanni in in situ coral nurseries. In P. evermanni, Fusion Guard Tiles increased lateral tissue growth 2.6-fold and three-dimensional tissue surface area growth by >2.7-fold after 6 months compared with conventional substrates. After 12 months, colony height and volume were approximately 4.0-fold and 2.2-fold greater, respectively, while complete fragment fusion occurred only on Fusion Guard Tiles. In S. pistillata, Coral Guard Plugs increased lateral tissue growth by [~]1.7-fold. Microcomputed tomography revealed 10-13% higher skeletal density in both species. In P. evermanni, Fusion Guard Tiles also increased symbiont density by 70% and tissue protein content by [~]2.5-fold relative to controls. Together, these findings demonstrate that Coral Guard substrates suppress algal competition while accelerating coral growth, skeletal development, and microfragment fusion, providing a scalable, low-maintenance technology to enhance coral nursery productivity and reef restoration.

Human activities are driving widespread degradation of natural ecosystems, with coral reefs among the most affected. While the impacts of climate change and pollution on coral reefs are well documented, the ecological consequences of recreational scuba diving, a rapidly growing industry, remain less understood. Namely, few studies have explored how diving influences trait diversity of coral reef fish assemblages, a key dimension of ecosystem resilience. Here, we investigated spatial variation in benthic composition and fish trait diversity across reef sites in Utila, Honduras, an island heavily reliant on dive tourism. We surveyed five sites of varying levels of diving intensity to quantify benthic cover and fish assemblages. Contrary to expectations, sites with high diving intensity did not show reduced coral cover, with the most heavily dived site (Stingray Point) maintaining the highest overall coral cover. Algae, however, dominated the benthos across all sites. While functional richness was maintained across the diving intensity gradient, functional composition shifted significantly among sites. This compositional shift was driven primarily by the Von Bertalanffy growth coefficient (k). Sites with low hard coral cover but higher benthic heterogeneity harboured fish communities dominated by fast-growing, early maturing species, whereas high hard coral cover sites supported assemblages of slower-growing, later-maturing species. Benthic composition, rather than diving intensity, emerged as the primary filter of fish life-history strategies. These findings suggest that while current diving intensity may not erode the volume of functional trait space, it is associated with distinct benthic states that filter for specific life-history strategies. Our results highlight the importance of maintaining benthic heterogeneity in reef systems, even in the absence of obvious coral loss. As functional diversity underpins key ecosystem services, it is important that coral reef monitoring focuses on changes in trait composition rather than just simpler taxonomic diversity metrics. Achieving this in collaboration with dive operators to promote low-impact diving is essential to sustaining reef resilience in tourism-dependent regions like Utila.

The foundation of coral reef ecosystems centered around the nutritional relationship between corals and intracellular algal symbionts. Although these symbioses are highly obligate for coral hosts, many partnerships are re-established anew with each coral generation. Furthermore, climate change destabilizes the symbiosis, and the cellular mechanisms underlying successful symbiont colonization of hosts and host development, and how they are affected by thermal stress are poorly understood. Here, we explored the effect of algal species and thermal treatments on symbiont and host cell proliferation by offering Acropora tenuis larvae one of four algal species pre-exposed to elevated or ambient temperature. In addition, we characterized the cell-surface glycome of each species-temperature combination to understand its role in symbiont recognition and proliferation. We found that thermal pre-treatment negatively affected algal photosynthetic efficiency and initial symbiont density in hosts, but did not affect symbiont colonization rate or cell proliferation. In contrast, host cell proliferation was affected in a species-specific manner. Thermal pre-treatment of B. minutum and D. trenchii negatively affected host cell proliferation compared to control symbionts, whereas thermal treatment of S. microadriaticum did not affect developmental outcomes. Further, uptake of thermally pre-treated D. trenchii decreased host cell proliferation below that of larvae not offered any symbionts, indicating that this relationship is costly to host development despite the high thermal tolerance of this species. Algal surface glycan composition varied across species but not by thermal pre-treatment, suggesting reductions in density of thermally pre-treated algae may be due to changes in physiology rather than altered surface chemistry. Further, variation in glycan abundance across species did not track differences in colonization rate or symbiont density, hinting towards a smaller role of glycans in host-symbiont specificity.

Mass coral bleaching events driven by marine heatwaves are increasing in frequency and severity, yet the long-term recovery trajectories of surviving corals remain poorly understood. Here, leveraging a cohort of individual coral colonies with a decade of tracked environmental and bleaching history, we captured structural shifts in the coral thermal performance landscape. Specifically, we quantified thermal performance curves (TPCs) for photosynthesis and calcification in bleaching-resistant and bleaching-susceptible colonies of two ecologically dominant reef-building corals (Montipora capitata and Porites compressa) at four and six years following the 2019 marine heatwave in K[a]neohe Bay, Hawaii (2023 and 2025, respectively). Coral thermal performance shifted substantially between 2023 and 2025, and these shifts differed between species, bleaching phenotypes, and traits. In P. compressa, photosynthetic thermal optimum (Topt) shifted downward over time by 1.6{degrees}C across both phenotypes, suggesting recalibration toward prevailing conditions at the potential cost of future heat tolerance. In M. capitata, photosynthetic performance was lower in bleaching-susceptible corals in 2023 but converged by 2025, suggesting susceptible colonies recovered. In contrast, Topt of photosynthesis remained persistently higher in bleaching-resistant colonies, likely reflecting established symbiont communities. Critically, photosynthesis and calcification did not recover in parallel. Calcification TPCs for both phenotypes of M. capitata were stable across both timepoints, whereas calcification TPCs in P. compressa continued to change through 2025. These findings demonstrate that coral thermal performance is not static following heatwaves but continues to be reshaped over multi-year recovery periods, and that species-specific traits and strategies can fundamentally constrain the pace and coupling of physiological recovery. Furthermore, elevated thermal tolerance acquired through a heatwave can erode during prolonged periods of ambient temperatures. As recurrent bleaching events shorten recovery windows, understanding these dynamic physiological trajectories are essential for understanding and forecasting reef futures.

Flexibility in the coral-algal symbiosis has been proposed as a mechanism by which coral colonies may acclimatize to shifting environmental conditions, yet the rules governing when and why switching occurs remain unresolved. Here, I compile longitudinal data spanning 59 coral species, 26 years, and 95 globally distributed reefs to estimate switching probability at the colony-level across directional environmental change and thermal variability. Switching was neither universal nor random: the identity of the resident symbiont was the strongest predictor of switching, with Cladocopium-dominated and mixed communities showing the greatest flexibility. Transition probabilities were asymmetrical, with shifts toward Durusdinium consistently more probable than shifts away, regardless of starting genus. Among host species- level effects, morphological traits best explained switching propensity along changing environmental conditions, while both traits and phylogenetic history explained sensitivity to thermal variability, suggesting that these two dimensions of abiotic environments impose distinct selective pressures on the symbiosis. Most switching was ultimately transient; colonies had a 78% chance of reverting back to their original symbiont in the following year. Together, these results challenge the assumption that increased environmental variability and rising temperatures universally correlate with higher switching rates, and suggest instead that host traits, phylogeny, and resident symbiont identity may help identify the subset of taxa for which flexibility represents a viable acclimatization strategy under climate stress.

In this study, we investigate alliance formation and complexity in male Indo-Pacific bottlenose dolphins around Mikura Island using five years of data collected through underwater observations. Focusing on 18 mature males, we examined affiliative behaviors (proximity and rubbing), consortships, and associations. To determine male relationships, we evaluated a simple model (small units) and a complex model (large units). In both models, units were identified by association, and models were evaluated by the extent to which affiliative behaviors and consortship were concentrated within units. All types of behaviors were more concentrated within units determined by the complex model than the simple model, and thus the former was further investigated. The unit sizes determined by the complex model were three, seven, and eight, and variation in association frequency was observed within units. Within units, two to four males engaged in a single consortship irrespective of association frequency. Given that units are mediated by affiliative and cooperative relationships, it is reasonable to interpret units as alliances. Considering the variation in both alliance size and within-alliance relationships, as well as the fact that only a few males cooperate in a single consortship, we suggest that a multi-level structure is plausible in the Mikura community.

Octocoral colonies with unusual morphology were detected in September 2022 and October 2023 in two coastal areas east of Havana, Cuba, and tentatively identified as Unomia stolonifera. U. stolonifera is an invasive octocoral from the Indo-Pacific that was first reported in the Caribbean off Venezuela in the 2000s, where it has spread rapidly, smothering coral reefs and substantially altering benthic communities. After obtaining tissue samples from a Cuban octocoral colony, we re-examined the specimen using molecular barcoding of three mitochondrial regions (16S/ND2, mtMutS, COI) and the nuclear large ribosomal subunit (28S rRNA), and we unequivocally identified it as Xenia umbellata. X. umbellata, a native of the Red Sea, was first identified in southern Puerto Rico in October 2023 and has since been found in various marine ecosystems along the southern coast of the island. The presence of either invasive octocoral species in Cuba or elsewhere in the Caribbean would be of a serious environmental concern due to their documented tolerance, totipotentiality, propagation capacity and significant negative interactions with local benthic fauna. Attempts to eradicate the invasive soft coral colonies from Cuban waters have been initiated with apparent success, helping to control further expansion. The most likely introduction pathway is the accidental or intentional releases from the aquarium trade but transport via ballast water cannot be ruled out. We cannot discount the possibility of independent invasion events from different routes to Puerto Rico and Cuba occurring within a year of each other. Propagation from Cuba to Puerto Rico, or vice versa, which we consider highly improbable, would likely imply that soft coral populations may also have been established on Hispaniola but have remained undetected in the Dominican Republic and Haiti to date.

Giant clams are some of the largest bivalve molluscs. They form a vital partnership with Symbiodiniaceae dinoflagellates that supply most of their energetic requirements. However, the factors that shape giant clam-associated photosymbiont communities remain unknown. Here, we profiled Symbiodiniaceae communities using ITS2 metabarcoding in eight giant clam species (Hippopus hippopus, H. porcellanus, Tridacna crocea, T. derasa, T. gigas, T. maxima, T. noae and T. squamosa) from 11 sites across the Philippine archipelago. Symbiodiniaceae community structure was shaped by an interplay between giant clam host and environment. Most giant clams were dominated by members of a single symbiont genus, with Cladocopium as the most prevalent, followed by Durusdinium and Symbiodinium. However, giant clam hosts also exhibited flexibility in their symbiotic partners that was evident across sites. Differences in giant clam-associated symbiont communities may contribute to differences in holobiont function and adaptability to variable environments. These findings deepen our understanding of giant clam-Symbiodiniaceae associations, offering a framework for predicting how giant clams may be affected by increasingly stressful reef conditions and, more importantly, informing strategies to improve mariculture and conservation practices.

Crown-of-thorns sea star (CoTS), Acanthaster cf. solaris, outbreaks are a major cause of hard coral cover decline across the west Pacific, threatening coral reefs. Coral taxa vary in susceptibility to CoTS predation from preferred (Acropora spp.) to non-preferred (Porites spp.), yet the mechanisms underlying these differences are poorly understood. We investigated coral defenses during an ongoing CoTS outbreak in Mo'orea, French Polynesia by examining gene expression (including putative toxin genes) in healthy and actively predated colonies of a preferred (Acropora hyacinthus) and a non-preferred (Porites sp.) coral prey species. During predation, A. hyacinthus exhibited molecular signatures of cellular stress responses involving oxidative stress signalling, inflammation, and tissue proteolysis. In contrast, Porites sp. showed enrichment of genes involved in mitochondrial metabolic adjustment and aerobic metabolism, suggesting metabolic compensation to maintain cellular function. Furthermore, A. hyacinthus demonstrated a reactive defense behaviour by differentially expressing toxins (e.g., kunitz-type neurotoxins) while Porites sp. employed constitutive expression of all putative toxins regardless of active predation, suggesting a proactive defense strategy. Together, these findings suggest that preferred and non-preferred coral prey exhibit fundamentally different molecular and defensive strategies during CoTS predation, shedding light on the evolutionary arms race between corals and their predators.

Indomethacin and temperature shocks are both widely used to induce ephyra production in Cassiopea polyps, yet the combined effect of these stimuli on strobilation rate, ephyra viability, and polyp survivorship has not been systematically examined. We designed a full factorial experiment crossing five indomethacin concentrations (0, 10, 25, 50, and 75 {micro}M) with four temperature treatments (22, 25, 28, and 31{degrees}C) across three independent experimental trials, exposing a total of 288 individual Cassiopea xamachana polyps for 29 days. Overall, 207 of 288 polyps (71.9%) released at least one ephyra. Temperature was the stronger predictor of strobilation: higher temperatures substantially increased the probability of producing a healthy ephyra (log-odds: +0.327 per {degrees}C; {chi}{superscript 2} p = 6.5 x 10-5), while indomethacin had a smaller but significant positive effect (log-odds: +0.024 per {micro}M; {chi}{superscript 2} p = 0.035). The two stimuli acted independently without significant interaction on healthy ephyra production ({chi}{superscript 2} p = 0.87), although their interaction on total ephyra production (including unhealthy releases) was significant ({chi}{superscript 2} p = 1.0 x 10-9). Notably, low indomethacin concentrations (10 and 25 {micro}M) significantly increased the proportion of unhealthy ephyrae relative to seawater controls (paired t-tests: p = 0.035 and p = 0.006, respectively), while higher concentrations (50-75 {micro}M) did not. Polyp survivorship declined significantly at 28{degrees}C and 31{degrees}C but was unaffected by indomethacin. Trial replicate was the most statistically significant predictor of every outcome measured with the third trial producing near-universal strobilation but zero viable ephyrae, a result of an unidentified perturbation. These results indicate that temperature elevation to 28-31{degrees}C is the most reliable induction strategy for C. xamachana and that low indomethacin concentrations should be avoided when ephyra quality is paramount. We also note that cryptic batch-level variables can overwhelm controlled factors and should be addressed in future experimental designs.

The marine sponge Hymeniacidon perlevis is a globally-distributed species, likely because it has been extensively spread through human means. The status of this species in the Western Atlantic has been difficult to discern due to the presence of a morphologically similar species Hymeniacidon heliophila. Here, we have collected Hymeniacidon specimens from the H. heliophila type location and compared their morphology and genotypes to material from Europe, North and South America, and publicly available datasets. Specimens from the type location closely matched the original description of H. heliophila, and were morphologically indistinguishable from H. perlevis. Multilocus sequencing data confirm that these samples are indistinguishable from H. perlevis, and that the name H. heliophila should therefore be considered a junior synonym of H. perlevis. Analysis of a global cox1 dataset further revealed significantly higher genetic diversity in Europe than in the remainder of the world combined, supporting a European origin for the species and suggesting that all other genotyped populations are introductions. In the Western Atlantic, we confirm the presence of H. perlevis in the Gulf of Mexico, but contrary to some past reports, are unable to confirm its presence in the Caribbean. Our results clarify the taxonomy, biogeography, and recent history of one of the worlds most widespread marine sponges.

Sexual coral propagation is an emerging technique capable of producing large numbers of corals for coral transplantation and reef rehabilitation. In contrast to asexual coral propagation, sexual propagation increases genotypic diversity and can be used for selective breeding to enhance coral heat tolerance or other desirable traits. However, implementation at meaningful ecological scales is hindered by high mortality during early life stages, high costs associated with nursery rearing facilities, and labour-intensive outplanting methods. To overcome these issues, we developed the CoralAssist Plug (CAP), a ceramic device designed for the rapid and cost-effective outplanting of sexually propagated corals in large numbers that maximises post-outplant survivorship. CAPs combine three important functional features: 1) built-in microrefugia to protect juvenile corals from grazing, 2) a relatively small size, 3 by 1 cm, that is easy to handle and stack efficiently without compromising the survivorship of corals, and 3) a hole in the middle that facilitates handling and attachment. CAPs were settled with Acropora aff. digitifera and outplanted to a reef crest after 1 to 6 months of ex situ nursery rearing. A 3-person dive team was able to outplant ~120 CAPs in one 90-minute shallow dive (just over 2 minutes per CAP per person). With longer nursery durations of 6 months, it was possible to achieve 36 % yield (i.e., the proportion of devices with a surviving coral) 4-years post-outplant. With nursery durations shortened to 1 month, we were able to attain 24 % yield 3-years post-outplant. Microrefugia significantly enhanced post-outplant survivorship leading to an 11 % increase in yield 4 years post outplant compared to devices without microrefugia. Outplanted corals that had reached adult size, were self-attached and were reproductively mature after 4 years. Our results suggest that CAPs can play a meaningful role in reef rehabilitation by efficiently introducing sexually propagated corals into natural populations with clear applications to assisted evolution techniques, such as selective breeding.

Lipid peroxidation (LPO) is widely used as a biomarker of oxidative stress in coral bleaching research, yet its measurement remains poorly standardized across the field. A systematic review of the coral LPO literature reveals substantial variation in methodological approaches, including tissue fraction analysis, lysis protocols, assay choice, and normalization metrics, confounding cross-study comparison and obscuring the biological interpretation of results. We experimentally investigate two key sources of variation: the use of bulk holobiont vs separated host and algal symbiont fractions, and the choice of normalization metric. To do so, we used Montastraea cavernosa (n = 6 colonies) exposed to ambient (28C), heat stress (30.5C), and heat stress + artificial upwelling (AU; heat stress intermitted by daily pulses of cooler water, 30.5/27.5C) conditions in a controlled mesocosm experiment. Using a TBARS-based MDA assay with a lysis buffer optimized for coral tissue, we measured LPO separately in coral host and algal symbiont fractions across four time points throughout the day. Host MDA remained stable across all treatments and time points, consistent with either sufficient antioxidant buffering capacity or thermal acclimation over the experimental period. Algal symbiont MDA, in contrast, exhibited pronounced diel and treatment-specific dynamics, and the two fractions responses were decoupled from one another. Normalizing MDA to coral surface area instead of total protein content produced largely consistent diel and treatment patterns, but the two metrics diverged at specific time points, indicating that normalization choice is not interchangeable and can itself affect interpretation. Together, our literature review and empirical results demonstrate that host and algal symbiont LPO dynamics are not comparable when aggregated and argue for host-symbiont fraction separation and consistent, explicitly reported normalization as minimum standards for interpretable and cross-comparable coral LPO measurement.

Experimentally evolved, heat-tolerant algal symbionts (heat-evolved; HE) offer a promising means of enhancing coral holobiont thermotolerance under rapidly warming oceans. However, translating their benefits into restoration practices requires scalable delivery methods. Coral tissue fusion may provide one such pathway by facilitating HE symbiont transfer to wild corals; however, its feasibility remains largely untested. As an initial test, we paired adult isografts of Galaxea fascicularis and Psammocora columna hosting HE Cladocopium proliferum (SS8) with chemically bleached, SS8-naive recipients. Fusion was first observed after three days in G. fascicularis and nine days in P. columna. In both species, fusion was followed by increased pigmentation and photochemical efficiency at the recipients fusion interface relative to distal tissue and unfused controls. After [~]50 days, SS8 was detected at low levels (<3.5%) in 15/19 fused G. fascicularis recipients, although detection was also common among unfused horizontal-transmission controls maintained in the same water column (13/18). These findings provide the first empirical evidence that conspecific coral tissue fusion is associated with localised physiological recovery and can coincide with HE symbiont acquisition, while highlighting the need to distinguish tissue-mediated transfer from background horizontal transmission. Fusion may therefore represent a complementary pathway for beneficial symbiont delivery in assisted-evolution frameworks.