Coral Reefs

Photosynthetic dinoflagellates that live in symbiosis with corals (family Symbiodiniaceae) are fundamental for the survival of coral reef ecosystems. During coral bleaching events, it is assumed that these symbionts remain available in the water column, in sediments, or are seeded from unbleached coral colonies. Yet, this hypothesis has not been verified and it remains unclear whether some diversity of Symbiodiniaceae may be lost in the process. Culture methods have been developed for some Symbiodiniaceae, but for the vast majority of these photosynthetic symbionts, known culture methods are not successful at maintaining them for extensive periods. For these unculturable symbionts, cryopreservation, which places cells and tissues in suspended animation for days to decades, offers the best hope for saving the biodiversity of these crucial coral partners. Some cryopreservation processes use slow freezing, but if the cells are sensitive to low temperatures, as is the case for Symbiodiniaceae, then rapid freezing, called vitrification, is needed. We here, tested two published vitrification protocols that had been designed for algal symbionts extracted from Hawaiian corals, but we were unable to recover living symbionts after vitrification and warming. Therefore, we report a successful optimisation of the former vitrification protocols, which we tested on algal symbionts freshly extracted from three Hawaiian coral species, the development of ultra-rapid laser-warming cryopreservation techniques for symbionts, and banking procedures for algal symbionts. We also present some successful uptake of cryopreserved algal symbionts by coral larvae, although at a low rate. It is unclear why the former vitrification protocols failed but we propose that it may have been related to thermal stress and bleaching events that occurred on several occasions throughout the Hawaiian Islands. Maintenance of biodiversity is essential for sustaining functional, productive ecosystems with the adaptability to effectively recover from disturbances. By successfully cryopreserving and banking coral symbionts, we provide a critically needed component for securing Symbiodiniaceae biodiversity into the future.

Identifying processes that promote coral reef recovery and resilience is crucial as ocean warming becomes more frequent and severe. Sexual reproduction is essential for the replenishment of coral populations and maintenance of genetic diversity; however, the ability for corals to reproduce may be impaired by marine heatwaves that cause coral bleaching. In 2014 and 2015, the Hawaiian Islands experienced coral bleaching with differential bleaching susceptibility in the species Montipora capitata, a dominant reef-building coral in the region. We tested the hypothesis that coral bleaching resistance enhances reproductive capacity and offspring performance by examining the reproductive biology of colonies that bleached and recovered (B) and colonies that did not bleach (NB) in 2015 in the subsequent spawning seasons. The proportion of colonies that spawned was higher in 2016 than in 2017. Regardless of parental bleaching history, we found eggs with higher abnormality and bundles with fewer eggs in 2016 than 2017. While reproductive output was similar between B and NB colonies in 2016, survivorship of offspring that year were significantly influenced by the parental bleaching history (egg donor x sperm donor: B x B, B x NB, NB x B, and NB x NB). Offspring produced by NB egg donors had the highest survivorship, while offspring from previously bleached colonies had the lowest survivorship, highlighting the negative effects of bleaching on parental investment and offspring performance. While sexual reproduction continues in M. capitata post-bleaching, gametes are differentially impacted by recovery time following a bleaching event and by parental bleaching resistance. Our results demonstrate the importance of identifying bleaching resistant individuals during and after heating events. This study further highlights the significance of maternal effects through potential egg provisioning for offspring survivorship and provides a baseline for human-assisted intervention (i.e., selective breeding) to mitigate the effects of climate change on coral reefs.

Anthropogenic stressors threaten reefs worldwide and natural in situ coral reproduction may be inadequate to meet this challenge. Land-based culture can provide increased coral growth, especially with microfragments. We tested whether culture methods using different algal fouling communities could improve the growth and health metrics of microfragments of the Hawaiian coral, Porites compressa. Culture method fouling communities were: 1) similar to a reef environment (Mini Reef); 2) clean tanks managed to promote crustose coralline algae (Clean Start); and, 3) tanks curated beforehand with poorly-competing algae (Green Film) assessed in winter and summer months. The Green Film method during the winter produced the fastest microfragment mean growth at 28 days until the first row of new polyps developed and the highest tank metric scores. Time efficient, standardized methods for land-based culture designed to maximize growth and production of coral fragments will contribute considerably to the success of large scale restoration efforts.

Coral reefs globally are experiencing chronic stress leading to the deterioration of health and functionality. Analysis of size frequency distribution (SFD) of hard corals enables post hoc assessments of major demographic events (e.g., recruitment and mortality) that follow ecological disturbances. Here, we present an evaluation of current reef health, SFD and recruitment of 37 morpho-taxa in Northeast Peninsular Malaysia. Results highlight stress viable demographic structure of massive taxa (e.g., massive Porites) and significant differences of SFD across gradients of reef health, whereby degraded sites were predominantly characterized by negatively skewed (e.g., large colonies) and leptokurtic (e.g., high population turnover) distribution of dominant hard coral taxa. Ultimately, results suggest that locally coral reef degradation can exceed tipping points, after which annual monsoon conditions and degraded reef substrates interact to reinforce and manifest negative feedback loops, thereby impeding demographic recovery, and altering coral SFD and population assemblage.

Coral reefs are facing increasingly devasting impacts from ocean warming and acidification due to anthropogenic climate change. In addition to reducing greenhouse gas emissions, potential solutions have focused either on reducing light stress during heating, or the potential for identifying or engineering "super corals". These studies, however, have tended to focus primarily on the bleaching response of corals, and assume that corals that bleach earlier in a thermal event are more likely to die. Here, we explore how survival, potential bleaching, and coral skeletal growth (as branch extension and densification) varies for conspecifics collected from distinctive reef zones at Heron Island on the Southern Great Barrier Reef. A series of reciprocal transplantation experiments were undertaken using the dominant reef building coral (Acropora formosa) between the highly variable reef flat and the less variable reef slope environments. Coral colonies originating from the reef flat had higher rates of survival and thicker tissues but reduced rates of calcification than conspecifics originating from the reef slope. The energetics of both populations however benefited from greater light intensity offered in the shallows. Reef flat origin corals moved to the lower light intensity of reef slope reduced protein density and calcification rates. For A. formosa, genetic difference, or long-term entrainment to a highly variable environment, appeared to promote coral survival at the expense of calcification. The response divorces coral resilience from carbonate coral reef resilience, a response that was further exacerbated by reductions in irradiance. As we begin to discuss interventions necessitated by the CO2 that has already been released to the atmosphere, we need to prioritise our focus on the properties that maintain valuable carbonate ecosystems. Rapid and dense calcification by corals such as branching Acropora is essential to the ability of carbonate coral reefs to rebound following disturbances events, but may be the first property that is sacrificed to enable coral genet survival under stress.

AimThe Indo-Pacific is the worlds largest marine biogeographic region. It is characterised by different degrees of connectivity among its subregions, and harbours the majority of demosponge species currently known to science. Comparisons between several regional sponge faunas have been undertaken in the past, mostly based on identifying the sponge species morphologically. The Sponge Barcoding Project, in tandem with other regional DNA taxonomy campaigns, provides one of the largest DNA-based taxonomic data collections from sponges of the Indo-Pacific. Here, we utilise the sponge barcoding data in the largest molecular biodiversity study of sponges to date, which reveals patterns of shallow-water demosponge faunal connectivity, endemism, and distribution in the Indo-Pacific with a level of resolution unavailable in prior morphology-based studies. LocationDemosponge specimens in this study cover 13 marine provinces of the Indo-Pacific, from the Red Sea to South East Polynesia. MethodsWe classified demosponge barcodes using the ribosomal subunit (28S rDNA) of 1,910 sponge samples into molecular operational taxonomic units (MOTUs). MOTU composition of the 13 marine provinces was compared based on Jaccard and Sorenson dissimilarities, and other biodiversity indices. ResultsOur data corroborated high levels of endemism among demosponges. Faunal overlaps were revealed between the Red Sea and the Gulf, which displayed relatively small connectivity with other marine provinces of the Western Indian Ocean. In the Western Indian Ocean, we observed a strong faunistic boundary to the Central Indo-Pacific. The Polynesian sponge faunas were comparatively isolated marine provinces of the Central Indo-Pacific. Main conclusionsOur data corroborate case studies on sponges that generally reject the presence of cosmopolitan or otherwise widespread sponge species, instead revealing high levels of regional endemism. This is consistent with similar observations and hypotheses in other marine invertebrates. Connectivity among Indo-Pacific marine provinces differs for demosponges in many aspects from that of other marine taxa, such as corals and fishes, probably due to their shorter pelagic larval phase.

With the increased frequency of marine heatwaves and related coral mass mortality events, it is imperative that we improve our understanding of coral reef recovery processes including how benthic community compositions can change over time. Coral reef benthic communities are influenced by many abiotic factors, but on most reefs local anthropogenic disturbances overshadow these factors thus obscuring their influence. Here, we leverage a dataset from a coral reef with very minimal local anthropogenic disturbance - the uninhabited southern coast of the worlds largest atoll (Kiritimati) - to assess spatial variation in benthic community composition three years after the mass coral mortality event driven by the 2015-2016 El Nino. Across forereef sites ranging from 7 to 22 m, scleractinian coral cover remained very low (6.9 {+/-} 0.4 % SE) while soft coral cover was < 1%. Coral cover was highest at deep sites (18-22 m compared to sites at 7-10 m depth) and exposed locations, where stress-tolerant corals likely made up a larger proportion of the coral community before the mass mortality event. Higher cover of crustose coralline algae at shallow exposed sites, fleshy macroalgae at deep sites, and turf algae at exposed locations were consistent with taxa-specific preferences for light, wave action, and sedimentation. The abundances of the most common genera of juvenile coral (Acropora and Pocillopora) were still low (< 1 juvenile colony per genus per site) and varied only with depth. These findings demonstrate how variation in pre-mortality coral composition can lead to differences in post-mortality benthic communities on low disturbance coral reefs.

The symbiotic relationship between coral and its endosymbiotic algae, Symbiodiniaceae, greatly influences the hosts potential to withstand environmental stress. To date, the effects of climate change on this relationship has primarily focused on adult corals. Uncovering the effects of environmental stress on the establishment and development of this symbiosis in early life stages is critical for predicting how corals may respond to climate change. To determine the impacts of future climate projections on the establishment of symbionts in juvenile corals, ITS2 amplicon sequencing of single coral juveniles was applied to Goniastrea retiformis and Acropora millepora before and after exposure to three climate conditions of varying temperature and pCO2 levels (current and RCP8.5 in 2050 and 2100). Compared to ambient conditions, juvenile corals experienced shuffling in the relative abundance of Cladocopium (C1m, reduction) to Durusdinium (D1 and D1a, increase) over time. We calculated a novel risk metric incorporating functional redundancy and likelihood of impact on host physiology to identify the loss of D1a as a low risk to the coral compared to the loss of "higher risk" taxa like D1 and C1m. Although the increase in stress tolerant Durusdinium under future warming was encouraging for A. millepora, by 2100, G. retiformis communities displayed signs of symbiosis de-regulation, suggesting this acclimatory mechanism may have species-specific thresholds. These results emphasize the need for understanding of long-term effects of climate change induced stress on coral juveniles and their potential for increased acclimation to heat tolerance through changes in symbiosis. Originality StatementHere we assessed changes in the uptake and establishment of Symbiodiniaceae in the early lifehistory stages of two coral species under future climate scenarios. Our study represents the first such assessment of future climate change projections (increased temperature and pCO2) influencing Symbiodiniaceae acquisition and specifically shows a community structure dominated by the stress tolerant genus Durusdinium. We also develop a novel risk metric that includes taxonomic function and redundancy to estimate the impact of symbiont taxa changes on coral physiology. Through the risk metric, we relate the stress-induced changes in symbiont community structure to the likelihood of functional loss to better understand the extent to which these changes may lead to a decrease in coral health.

High mortality rates of juvenile corals hinder both the natural recovery of populations and the successful implementation of restoration efforts. Grazing is a significant cause of juvenile coral mortality, and grazer exclusion devices have been shown to increase juvenile coral survivorship. However, most experiments have used cages that typically alter water flow and light conditions and exclude grazers of most sizes, making it difficult to quantify the effects of large grazers alone. Here, we test whether deterring large grazers can increase the survival and growth of six-month-old Acropora digitifera juveniles outplanted to a shallow reef crest, using arrangements of two or four long or short masonry nails that selectively exclude larger grazers (e.g., parrotfish) while minimising abiotic changes. By the end of our study, colonies with deterrents had significantly larger planar area (almost tenfold for the most effective treatment), more branches, greater height, and enhanced survival than those without deterrents. A critical period is the first week after outplanting when colonies with deterrents had significantly less tissue loss from grazing than those without. Less tissue loss in the first week was associated with significantly higher survival over the following 14 months, with an almost threefold improvement for the most effective treatment. For heavily grazed systems, our study highlights the importance of incorporating grazing deterrents into outplant devices to counteract the negative impact of large grazers on outplanted juvenile coral survival and boost restoration success.

AO_SCPLOWBSTRACTC_SCPLOWCaribbean reefs have experienced unprecedented changes in the past four decades. Of great concern is the perceived widespread shift from coral to macroalgal dominance and the question of whether it represents a new, stable equilibrium for coral-reef communities. The primary causes of the shift -- grazing pressure (top-down), nutrient loading (bottom-up) or direct coral mortality (side-in) -- still remain somewhat controversial in the coral reef literature. We have attempted to tease out the relative importance of each of these causes. Four insights emerge from our analysis of an early regional dataset of information on the benthic composition of Caribbean reefs spanning the years 1977-2001. First, although three-quarters of reef sites have experienced coral declines concomitant with macroalgal increases, fewer than 10% of the more than 200 sites studied were dominated by macroalgae in 2001, by even the most conservative definition of dominance. Using relative dominance as the threshold, a total of 49 coral-to-macroalgae shifts were detected. This total represents [~]35% of all sites that were dominated by coral at the start of their monitoring periods. Four shifts (8.2%) occurred because of coral loss with no change in macroalgal cover, 15 (30.6%) occurred because of macroalgal gain without coral loss, and 30 (61.2%) occurred owing to concomitant coral decline and macroalgal increase. Second, the timing of shifts at the regional scale is most consistent with the side-in model of reef degradation, which invokes coral mortality as a precursor to macroalgal takeover, because more shifts occurred after regional coral-mortality events than expected by chance. Third, instantaneous observations taken at the start and end of the time-series for individual sites showed these reefs existed along a continuum of coral and macroalgal cover. The continuous, broadly negative relationship between coral and macroalgal cover suggests that in some cases coral-to-macroalgae phase shifts may be reversed by removing sources of perturbation or restoring critical components such as the herbivorous sea urchin Diadema antillarum to the system. The five instances in which macroalgal dominance was reversed corroborate the conclusion that macroalgal dominance is not a stable, alternative community state as has been commonly assumed. Fourth, the fact that the loss in regional coral cover and concomitant changes to the benthic community are related to punctuated, discrete events with known causes (i.e. coral disease and bleaching), lends credence to the hypothesis that coral reefs of the Caribbean have been under assault from climate-change-related maladies since the 1970s.

Marine broadcast spawners typically exhibit bipartite life-histories with distinct pelagic larvae and benthic phases. The transition between phases shapes benthic populations, but the rate of larval arrival to a reef is largely unknown due to challenges in accurately measuring supply. Once larvae arrive to a reef, reduced current flow and velocity, facilitate the transition from the water column to the benthos for inefficient swimming larvae. Yet, for coral reefs characterised by complex hydrodynamics and tides, slack current conditions typically last 1.5-3 hours and it remains unclear if such short retention periods drive significant recruitment. This study mechanistically examined the effects of water retention on the settlement of coral larvae from the water column to the benthos and subsequent longer-term recruitment over 15-months. Brief periods of slack currents (<3-hours) retained larvae in unconstrained larval supply treatments, resulting in settlement rates 40-times higher than natural, background rates. Constrained and longer retention of larvae under nets for 2.5- and 24-hours resulted in 4-7-times higher initial settlement than the unconstrained treatment and 305-times higher than background rates. However, after 15-months, similar numbers of surviving recruits were observed across all larval supply treatments, highlighting the effects of density-dependent population regulation. Observations from recruitment tiles show survival rates of coral recruits after 15-months were low (<0.25), even though gregarious settlement behaviour and settlement close to tile edges improved survival. In contrast, observations from the natural substrate show survival rates were 2.5-3.5-times higher than tiles after 15-months, indicating density-independent survival due to optimal niche space and less space limitation. Therefore, when larval supply is high and gregarious behaviour prominent, key vital rates including recruitment and mortality derived from settlement tiles are likely overestimated, as substrate and microhabitat properties between tiles and natural reef environment vary. Overall, our study highlights the prominent role of slack current conditions and local retention of larvae in facilitating the supply-to-settlement transition, and how this interacts with density-dependent processes post-settlement. Our findings underscore the need to investigate how the interaction strengths of pre-and post-settlement processes modulate early coral recovery to best model recovery trajectories for conservation and restoration prioritisation.

Herbivores play an integral part in maintaining the health of coral reefs by suppressing the growth of algae and accumulation of sediment and facilitating coral growth. However, in predator-depleted systems where densities of herbivores are unnaturally high, grazing can have detrimental effects on corals through excessive bioerosion. Yet, these benefits and costs are rarely investigated concurrently, especially in eutrophic systems where grazers may play a disproportionate role. We used a year-long exclusion experiment to elucidate the effect of natural densities of the dominant herbivore (the sea urchin Diadema setosum) on coral communities in a heavily fished and eutrophic system (Hong Kong, China). To assess benthic community response to grazing, we monitored the survival and growth of three locally abundant coral species (Pavona decussata, Platygyra carnosus and Porites sp.), algal and sediment accumulation, and bioerosion of coral skeletons across seasons. We found that urchins maintained our experimental coral assemblages, and when excluded, there was a 25 to 75-fold increase in algal-sediment matrix accumulation. Contrary to predictions, there was no general response of corals to urchin presence; Porites sp. survivorship increased while P. decussata was unaffected, and growth rates of both species was unchanged. Surprisingly, P. carnosus experienced higher mortality and bioerosion of up to 33% of their buoyant weight when urchins were present. Therefore, under natural densities, sea urchins clear substrate of algae and sediment, increase survival, maintain growth rates and health of coral assemblages, yet can accelerate the bioerosion of species with porous skeletons following mortality.

Thermal variability can render corals stress resistant through a phenomenon coined as "stress-hardening induced by environmental priming". Fluctuations that involve high temperature peaks have been commonly investigated, however, the effects of a stress-hardening stimulus generated by cold-water pulses has rarely been studied. Offshore island reefs in the Andaman Sea offer an ideal natural setting to study these effects, as cooling water of internal waves induce strong variability with peak intensity in January to June and absence in August to November. While western island shores are exposed to this stimulus, eastern shores remain sheltered. This study examined (1) whether corals from exposed reefs were more heat stress resistant compared to stimulus-sheltered conspecifics and (2) whether this trait can last in the absence of the stimulus. We quantified the thermal stress resistance in two ecologically important coral species, Pocillopora sp. and Porites sp., from the two island shores, during the two seasons. Coral bleaching intensity and photosynthetic efficiency of algal symbionts were measured as response variables after a short-term heat stress assay (24-48 h, 34 {degrees}C) to assess thermal stress resistance. Stress responses of all stimulus-exposed corals were either undetectable (during the season of stimulus presence) or very weak (during stimulus absence), while corals from the stimulus-sheltered shore responded strongly to heat stress irrespective of the season. Hence, thermal resistance was overall greater in corals originating from the stimulus-exposed shore, but it was slightly diminished during the season of stimulus absence, emphasizing the relevance of stimulus recurrence in maintaining the resistance trait. We exemplify that the stimulus of fluctuating low temperature pulses successfully induced stress-hardening in corals. This suggests that priming stimuli do not necessarily need to transgress certain upper thermal thresholds, but can also touch on lower thresholds to be effective. Even more, we argue that cooling pulses might represent a safer stress-hardening regime, since warming-stress accumulation can be avoided. More research is required to obtain a better understanding of environmental priming, but current findings should encourage the development of artificial stress-hardening approaches to enhance coral resistance in reef restoration efforts.

Scleractinian corals exhibit wide intra-specific phenotypic variations. However, the extent to which these variations are explained by genotypic variation or phenotypic plasticity remains unclear. To elucidate this question, we devised a replicated experiment in which nine Montipora capitata coral colonies were cut into six pieces each, three of which were placed in shaded conditions (with a 73% reduction in light intensity) whereas the other three were kept in natural conditions as a control. After one year, we detected statistically significant morphological differences between corals of the same genotypes grown in different light environments, but no significant change in symbiont community structure. Colonies kept in control conditions exhibited high surface complexity and converged towards more digitate or corymbose morphs compared to shaded corals, which exhibited planar-like surfaces and converged toward laminar and foliose forms. Our data demonstrate the high level of light-driven phenotypic plasticity of Montipora capitata and suggest a trade-off between the amount of biomass per space area and the amount of absorption of incident light.

O_LIGlobal climate change is altering coral reef ecosystems. Notably, marine heat waves are producing widespread coral bleaching events that are increasing in frequency, with projections for annual bleaching events on reefs worldwide by mid-century. C_LIO_LIThe response of corals to elevated seawater temperatures can be modulated by abiotic factors at site of origin and dominant endosymbiont type, which can result in a shift in multiple coral traits and drive physiological legacy effects that influence the trajectory of reef corals under subsequent thermal stress events. It is critical, therefore, to evaluate the potential for shifting physiological and cellular baselines driven by these factors in in situ bleaching (and recovery) events. Here, we use the back-to-back regional bleaching events of 2014 and 2015 in the Hawaiian Islands and subsequent recovery periods to test the hypothesis that coral multivariate trait space (here termed physiotype, sensu (Van Straalen, 2003) shift in multiple bleaching events, modulated by both environmental histories and symbiotic partnerships (Symbiodiniaceae). C_LIO_LIDespite fewer degree heating weeks in the first-bleaching event relative to the second (7 vs. 10), bleaching severity in a dominant reef building coral on Hawaiian reefs, Montipora capitata, was greater (~70% vs. 50% bleached cover) and differences due to environmental history (reef site) were more pronounced. Melanin, an immune cytotoxic response, provided an initial defense during the first event, potentially priming antioxidant activity, which peaked in the second-bleaching event (i.e., a legacy effect). While magnitude of bleaching differed, immune response patterns were shared among corals harboring heat-sensitive and heat-tolerant Symbiodiniaceae. This supports a pattern of increased constitutive immunity in corals resulting from repeat bleaching events, with greater specialized enzymes (catalase, peroxidase, superoxide dismutase) and attenuated melanin synthesis. C_LIO_LIThis study demonstrates bleaching events have implications for reef corals beyond shaping their ecological assemblages. These events can change the magnitude and/or identity of response variables contributing to physiotype, thus generating physiological legacies carried over into the future. Quantifying baseline coral physiotypes and tracking their shifts will be critical to understanding and forecasting the effects of increased bleaching frequency on coral biology and ecology in the Anthropocene. C_LI

Cartagena Bay, Colombia, experienced historical changes in water quality, mainly due to dredging and channelization of the Canal del Dique, which connects the bay with the Magdalena River. In 1981 the largest dredging events occurred in the Canal del Dique, which negatively affected the water quality in the bay. In this bay, the coral reef of Varadero depicts high coral diversity and large coral colonies, showing apparent signs of a healthy ecosystem, under highly turbid and polluted waters. Here, we evaluated the potential effects of historical water quality changes and environmental variables on the coral skeletal growth of Orbicella faveolata. We obtained coral growth information from 65 years in the period 1951-2015. Coral skeletal density was 0.73 g cm-3, linear extension 1.02 cm yr-1, and calcification 0.74 g cm-2 yr-1. After 1981, significant changes in coral growth and luminescence were found: skeletal density decreased (9.9%), linear extension increased (6.6%), and skeletal luminescence was less intense (1.6%). In overall, Atlantic Multidecadal Oscillation (AMO) data explained changes in skeletal density (8-10%) and linear extension (7-19%). Air temperature explained changes in skeletal luminescence (22-45%). Water flow of the Canal del Dique did not contribute significantly to any coral growth and luminescence variables. The growth of O. faveolata in Varadero Reef was characterized by low density skeletons and an accelerated linear extension, apparently influenced by the dredging events of 1981. Further research is required to understand coral growth responses and resilience to the conditions of high turbidity, pollution, and low light in Cartagena Bay.

The global climate crisis has heightened the urgency for developing interventions to enhance resilience and recovery of coral reef ecosystems. However, research programs are often bottlenecked by availability of coral early life stage material due to the seasonal (annual) nature of coral mass spawning events. Here, we present a proof-of-concept of "out-of-season" coral spawning, utilising advanced aquarium control technology to induce spawning in multiple key Great Barrier Reef (GBR) coral species held in long-term indoor aquaria. By developing a 6-month offset environmental profile encompassing seasonal temperature, photoperiod, and lunar profiles, we successfully induced synchronised mass coral spawning during austral autumn/winter (May - June) over consecutive years in 2022 and 2023. We also "phase-shifted" the hour of sunset by five hours on spawning nights, creating a more favourable time window (i.e., minimising late nights) for gamete fertilisation. The timing of gamete release in captive corals closely matched previous GBR field observations for both nights after full moon (NAFM) and time after sunset (TAS). Gamete fertilisation was successful for six GBR species: Acropora millepora, Acropora loripes, Acropora hyacinthus, Acropora elseyi, Acropora austera, and Montipora aequituberculata producing a total of 1.75 million larvae. We outline key physiological insights gained into environmental regulation of coral spawning synchronicity and discuss the potential for out-of-season spawning to accelerate various aspects of coral reproduction research and enhance the growing toolbox of active restoration strategies aimed at reversing global coral reef decline.

Recent increases in the frequency of mass coral bleaching and mortality events have caused shifts in species composition and rapid global reef decline. Genetic-based techniques, like assisted gene flow (AGF), offer the potential to enhance corals climate readiness by introducing genetic variation associated with heat tolerance into vulnerable populations. This method remains untested in the wild during a marine heatwave. To this end, we selectively bred AGF corals by crossing parent Acropora tersa corals collected across five Great Barrier Reef (GBR) locations spanning a thermal and bleaching gradient. Breeding produced intra- and inter-regional offspring that were then deployed to a central GBR reef. This deployment reef was subsequently hit by a marine heatwave (>31.4{degrees}C for 17 days and >6 Degree Heating Weeks). Heat tolerance-associated traits (survival, growth, and bleaching) were compared between AGF offspring and a native control cross over the 95 days in the wild. Overall, AGF offspring had 4x greater odds of survival compared to controls, and 2x greater odds compared to northern juveniles. Growth rates were 14% higher in control juveniles compared to the mean growth rate across all AGF crosses. Interestingly, heat-stress assays (32{degrees}C) of the parental adult corals showed similar patterns to their offspring, with higher survival and lower bleaching of corals from warmer northern reefs. Taken together, these findings providing critical support that the selective breeding of AGF corals can provide enhanced survival under marine heatwave conditions in the wild. It also suggests further evaluation is needed for trait-specific responses to effectively match donor and recipient reefs in restoration planning.

Natural bleaching events provide an opportunity to examine how local scale environmental variation influences bleaching severity and recovery. During the 2020 marine heatwave, we documented widespread and severe coral bleaching (75 - 98% of coral cover) throughout the Keppel Islands in the Southern inshore Great Barrier Reef. Acropora, Pocillopora and Porites were the most severely affected genera, while Montipora was comparatively less susceptible. Site-specific heat-exposure metrics were not correlated with Acropora bleaching severity, but recovery was faster at sites that experienced lower heat exposure. Despite severe bleaching and exposure to accumulated heat that often results in coral mortality (degree heating weeks [~] 4 - 8), cover remained stable. Approximately 94% of fate-tracked Acropora millepora colonies survived, perhaps owing to reduced irradiance stress from high turbidity, heterotrophic feeding, and large tidal flows that can increase mass transfer. Severe bleaching followed by rapid recovery, and the continuing dominance of Acropora populations in the Keppel Islands is indicative of high resilience. These coral communities have survived an 0.8 {degrees}C increase in average temperatures over the last 150 years. However, recovery following the 2020 bleaching was driven by the easing of thermal stress, which may challenge their recovery potential under further warming. Open Research StatementData are not yet provided but are being compiled. Upon acceptance data will be archived on GitHub.

Using a restricted set of behavioral responses, corals must obtain sufficient light to maximize photosynthesis while simultaneously avoiding predation and molecular damage from UV radiation. This study investigates the polyp behavioral response of the Caribbean octocoral Briareum asbestinum to shading, and how this response influences reactions to a simulated predator cue. In experiment I, we measured changes in polyp extension before and after a shade structure was placed over colonies on a shallow patch reef in the Florida Keys. In experiment II, changes in polyp extension were measured following a simulated predator cue for both shaded and un-shaded colonies. Experiment I demonstrates that B. asbestinum possesses a mechanism for detecting changes in light intensity and responds by manipulating the extension of its polyps. Following polyp retraction due to a predator cue in experiment II, the temporal pattern of polyp re-extension differed between shaded and non-shaded colonies, and at the end of the observation period, shaded colonies had a greater proportion of extended polyps than non-shaded colonies, consistent with the results of experiment I. This research provides novel and valuable insights into the behavior of a common and important Caribbean octocoral and will serve as a foundation for future research pertaining to the physiological processes involved.