Scleractinian Corals Research Articles

Microinjection, gene knockdown, and CRISPR-mediated gene knock-in in the hard coral, Astrangia poculata.

Cnidarians have become valuable models for understanding many aspects of developmental biology including the evolution of body plan diversity, novel cell type specification, and regeneration. Most of our understanding of gene function during early development in cnidarians comes from a small number of experimental systems including the sea anemone, Nematostella vectensis. Few molecular tools have been developed for use in hard corals, limiting our understanding of this diverse and ecologically important clade. Here, we report the development of a suite of tools for manipulating and analyzing gene expression during early development in the northern star coral, Astrangia poculata. We present methods for gene knockdown using short hairpin RNAs, gene overexpression using exogenous mRNAs, and endogenous gene tagging using CRISPR-mediated gene knock-in. Combined with our ability to control spawning in the laboratory, these tools make A. poculata a tractable experimental system for investigative studies of coral development. Further application of these tools will enable functional analyses of embryonic patterning and morphogenesis across Anthozoa and open new frontiers in coral biology research.

Fine‐scale interplay between decline and growth determines the spatial recovery of coral communities within a reef

As coral reefs endure increasing levels of disturbance, understanding recovery patterns of reef‐building hard corals is paramount to assessing the sustainability of these ecosystems. At local scales, coral recovery slows down; however, it's unclear how this trend propagates across spatial scales due to the inherent complexity of coral dynamics. In this paper, we aimed to learn about fine scale heterogeneity of coral dynamics and explore implications for assessing coral recovery at larger spatial scales. We developed a spatio‐temporal statistical model to estimate long‐term trajectories of three types of corals and predict their recovery patterns at unobserved locations within a reef. Then, model predictions were used to derive metrics that capture the interplay between coral growth and decline from disturbance(s) across time, space and growth morphology. This model is developed in the context of a substantive case study at Heron Reef using a high spatio‐temporal resolution dataset. Our results revealed that successful coral community recoveries took place in different habitats of Heron Reef and associated with various reasons. Branching corals recovered in the southern slope, due to fast growth in locations that were previously abundant. Plate corals flourished in the northern slope due to fast growth, despite a large decline and low baseline cover. They also recovered in the southern slope but in this case there was both a low decline and baseline cover. At Heron Reef, the recovery of coral communities followed specific conditions that were acting at a fine scale in a complex and heterogeneous way within habitat. This implies that capturing the variability of fine‐scale coral dynamics is an important first step to detect accurate signals of coral recovery at larger spatial scales. The approach proposes here can be further extend to the scale of a reef and beyond enabling assessment of recovery patterns representative at management scales.

Sclerochronological characteristics of Orbicella faveolata in Cayo Arenas, a remote coral reef from the Gulf of Mexico.

During coral calcification in massive scleractinian corals, a double annual banding of different densities (high- and low-density) is formed in their skeletons, which can provide a retrospective record of growth and the influence of environmental conditions on the coral's lifespan. Evidence indicates that during the last decades, the reduction in coral calcification rate is attributed to the combination of global stress factors such as Sea Surface Temperature (SST) and local anthropic stressors. Yet, coral growth trajectories can vary between regions and coral species, where remote locations of coral reefs can act as natural laboratories, as they are far from the harmful effects of direct anthropogenic stressors. The present study reports historical chronology over a 24-year period (1992-2016) of coral extension rate (cm yr-1), skeletal density (g cm-3), and calcification rate (g cm-2 yr-1) of the reef-building coral Orbicella faveolata at the remote reef Cayo Arenas, Campeche Bank, in the south-eastern Gulf of Mexico. The relationships between the three sclerochronological features show that O. faveolata uses its calcification resources to build denser skeletons. Chronological trends indicate that coral extension increased, skeletal density and calcification rate decreased (33% calcification rate) over time. The results reveal that despite the remoteness of the locality the maximum SST has been increased, and the coral calcification rate decreased over time. If the temperature continues to rise, there is a conceivable risk of experiencing a decline in reef-building coral species. This scenario, in turn, could pose a significant threat, endangering not only the framework of coral reefs but also their ecological functionality, even within remote Atlantic reef ecosystems.

Opportunistic observations of reproductive mode, larval settlement and development of a New Zealand deep-sea stony coral, Goniocorella dumosa

Opportunistic observations of reproductive mode, larval settlement and development of a New Zealand deep-sea stony coral, Goniocorella dumosa

Recent and rapid reef recovery around Koh Phangan Island, Gulf of Thailand, driven by plate-like hard corals.

Mass bleaching events and local anthropogenic influences have changed the benthic communities of many coral reefs with pronounced spatial differences that are linked to resilience patterns. The Gulf of Thailand is an under-investigated region with only few existing datasets containing long-term developments of coral reef communities using the same method at fixed sites. We thus analyzed benthic community data from seven reefs surrounding the island of Koh Phangan collected between 2014 and 2022. Findings revealed that the average live hard coral cover around Koh Phangan increased from 37% to 55% over the observation period, while turf algae cover decreased from 52% to 29%, indicating some recovery of local reefs. This corresponds to a mean increased rate of coral cover by 2.2% per year. The increase in live hard coral cover was mainly driven by plate-like corals, which quadrupled in proportion over the last decade from 7% to 28% while branching corals decreased in proportion from 9% to 2%. Furthermore, the hard coral genus richness increased, indicating an increased hard coral diversity. While in other reefs, increasing live hard coral cover is often attributed to fast-growing, branching coral species, considered more susceptible to bleaching and other disturbances, the reefs around Koh Phangan recovered mainly via growth of plate-like corals, particularly of the genus Montipora. Although plate-like morphologies are not necessarily more bleaching tolerant, they are important for supporting reef fish abundance and structural complexity on reefs, aiding reef recovery and sturdiness. Hence, our findings indicate that the intensity of local stressors around Kho Phangan allows reef recovery driven by some hard coral species.

РЕНТГЕНОВСКАЯ ВИЗУАЛИЗАЦИЯ КАК МЕТОД ИДЕНТИФИКАЦИИ ФРАГМЕНТОВ ГЛУБОКОВОДНЫХ СООБЩЕСТВООБРАЗУЮЩИХ СКЛЕРАКТИНИЕВЫХ КОРАЛЛОВ

Deep-sea colonial Scleractinia (Anthozoa: Hexacorallia) are indicator species of vulnerable marine ecosystems known as deep-sea coral reefs. The number of species of deep-sea community-forming colonial Scleractinia is small and specimens of good preservation, especially those collected in a live state, can be easily identified to the species level. Identification of fragments, especially those of the basal part of colonies, can be difficult. We have shown that X-ray examination can effectively distinguish colony fragments of the widespread deep-sea community-forming scleractinian corals Desmophyllum pertusum and Solenosmilia variabilis (Caryophylliidae). The skeleton of S. variabilis is considerably denser and less X-ray permeable compared to D. pertusum. The calyx cavities of the corallites of S. variabilis are visible only at the periphery of the fragment and practically do not extend to the outside. In D. pertusum, the cavities of the corallites can be deeply traced in the fragment body, they have a conical shape and considerably expand to the periphery. The proposed method of identification is inexpensive, does not require special sample preparation, and allows rapid identification of bulk material.

Iodine-to-calcium ratios in deep-sea scleractinian and bamboo corals

The distribution of dissolved iodine in seawater is sensitive to multiple biogeochemical cycles, including those of nitrogen and oxygen. The iodine-to-calcium ratio (I/Ca) of marine carbonates, such as bulk carbonate or foraminifera, has emerged as a potential proxy for changes in past seawater oxygenation. However, the utility of the I/Ca proxy in deep-sea corals, natural archives of seawater chemistry with wide spatial coverage and radiometric dating potential, remains unexplored. Here, we present the first I/Ca data obtained from modern deep-sea corals, specifically scleractinian and bamboo corals, collected from the Atlantic, Eastern Pacific, and Southern Oceans, encompassing a wide range of seawater oxygen concentrations (10–280 μmol/kg). In contrast to thermodynamic predictions, we observe higher I/Ca ratios in aragonitic corals (scleractinian) compared to calcitic corals (bamboo). This observation suggests a strong biological control during iodate incorporation into deep-sea coral skeletons. For the majority of scleractinian corals, I/Ca exhibits a covariation with local seawater iodate concentrations, which is closely related to seawater oxygen content. Scleractinian corals also exhibit notably lower I/Ca below a seawater oxygen threshold of approximately 160 μmol/kg. In contrast, no significant differences in I/Ca are found among bamboo corals across the range of oxygen concentrations encountered (15–240 μmol/kg). In the North Atlantic, several hydrographic factors, such as temperature and/or salinity, may additionally affect coral I/Ca. Our results highlight the potential of I/Ca ratios in deep-sea scleractinian corals to serve as an indicator of past seawater iodate concentrations, providing valuable insights into historical seawater oxygen levels.

Comparative transcriptome analysis reveals deep molecular landscapes in stony coral Montipora clade.

Introduction: Coral reefs, among the most invaluable ecosystems in the world, face escalating threats from climate change and anthropogenic activities. To decipher the genetic underpinnings of coral adaptation and resilience, we undertook comprehensive transcriptome profiling of two emblematic coral species, Montipora foliosa and Montipora capricornis, leveraging PacBio Iso-Seq technology. These species were strategically selected for their ecological significance and their taxonomic proximity within the Anthozoa class. Methods: Our study encompassed the generation of pristine transcriptomes, followed by thorough functional annotation via diverse databases. Subsequently, we quantified transcript abundance and scrutinized gene expression patterns, revealing notable distinctions between the two species. Results: Intriguingly, shared orthologous genes were identified across a spectrum of coral species, highlighting a substantial genetic conservation within scleractinian corals. Importantly, a subset of genes, integral to biomineralization processes, emerged as exclusive to scleractinian corals, shedding light on their intricate evolutionary history. Furthermore, we discerned pronounced upregulation of genes linked to immunity, stress response, and oxidative-reduction processes in M. foliosa relative to M. capricornis. These findings hint at the presence of more robust mechanisms in M. foliosa for maintaining internal equilibrium and effectively navigating external challenges, underpinning its potential ecological advantage. Beyond elucidating genetic adaptation in corals, our research underscores the urgency of preserving genetic diversity within coral populations. Discussion: These insights hold promise for informed conservation strategies aimed at safeguarding these imperiled ecosystems, bearing ecological and economic significance. In synthesis, our study seamlessly integrates genomic inquiry with ecological relevance, bridging the gap between molecular insights and the imperative to conserve coral reefs in the face of mounting threats.

Condition of Coral Diversity in Kuta Mandalika Coastal, Central Lombok Regency

Development and operational activities in KEK Mandalika can increase sedimentation of waters caused by erosion of construction material activities, this have an impact on coral reef ecosystems. Coral reef ecosystems have several important roles in support life of various aquatic organisms, Damage to the coral reef ecosystem directly and indirectly, sooner or later will threaten the sustainability of the use of these resources (social economy) and the safety of the community. Observations were conducted in KEK Mandalika coastal at 6 observation points less than 10 m. The results showed that the highest percentage of live coral cover was found in Kuta Mandalika coastal at PIT 4 area (30%, damaged category, moderate status). While the lowest percentage of coverage was at PIT 5, which was 2% (damaged category, bad status). Overall the percentage of coral cover in the Kuta Mandalika area is included in the damaged category. One of the reasons is because at the lowest tide on the beach, the volume of water is very small so that many hard corals are exposed to solar radiation. This limits the types of hard corals that can grow in the intertidal zone of Mandalika coastal. Genus diversity at this location is low, ranging from 0.0782 to 0.1288. Several genera of the Nephtheidae family dominate the observation sites and form colonies of the same genus with a fairly large distribution. The average value of environmental parameter measurements in the Mandalika coastal is included in the good category for soft coral habitat and growth.

Breeding and Selecting Corals Resilient to Global Warming.

Selective breeding of resilient organisms is an emerging topic in marine conservation. It can help us predict how species will adapt in the future and how we can help restore struggling populations effectively in the present. Scleractinian corals represent a potential tractable model system given their widescale phenotypic plasticity across fitness-related traits and a reproductive life history based on mass synchronized spawning. Here, I explore the justification for breeding in corals, identify underutilized pathways of acclimation, and highlight avenues for quantitative targeted breeding from the coral host and symbiont perspective. Specifically, the facilitation of enhanced heat tolerance by targeted breeding of plasticity mechanisms is underutilized. Evidence from theoretical genetics identifies potential pitfalls, including inattention to physical and genetic characteristics of the receiving environment. Three criteria for breeding emerge from this synthesis: selection from warm, variable reefs that have survived disturbance. This information will be essential to protect what we have and restore what we can.

Deriving fine-scale patterns of sea surface temperature in coral reef habitats using the Landsat 8 thermal infrared sensor

The available sea surface temperature (SST) products are too coarse to assess the fine-scale (<1 km) SST variations related to coral bleaching. In this study, we proposed an optimal SST inversion model using Landsat 8 thermal infrared sensor (TIRS) images to derive fine-scale SST patterns in the coral reef habitats of the Xisha Islands, South China Sea. Our study included two parts: 1) six SST inversion models were developed using the radiative transfer method and the split window (SW) algorithm in the hot season and cool season, from which the optimal SST inversion model was determined; and 2) the optimal model was applied to 47 Landsat 8 TIRS images to derive the SST spatial and temporal pattern among the geomorphic zones of six reefs in hot and cool season conditions. Compared with the measured sea temperature data and the verified MODIS SST products, the SST6 model using the SW algorithm was optimal, with an RMSE of approximately 0.64°C in the hot season. The average SST results usually had a pattern of reef flat > lagoon > reef slope/offshore sea. The reef flat was usually approximately 0.05°C–0.2°C hotter than the lagoon in the hot season. The SST in the lagoon also increased from south to north and the shallow lagoon was usually warmer than the deep lagoon in the hot season. Our results suggested that scleractinian corals in the reef flat and the lagoon were more susceptible to bleaching-level thermal stress than other geomorphic zones. During the cool season, the SST fluctuated markedly among coral reefs and geomorphic zones.

Characteristic and histological evidence of microplastic in scleractinian corals of Java Sea

Coral reefs are threatened by emerging microplastic pollution but only a few studies are available regarding the extent of contamination in coral reef systems in situ. For this research, we collected samples from the seawater, sediments, and coral colonies of the Panjang Island cluster and the Karimunjawa Archipelago, Java Sea. Microplastics were detected in all sample types. Based on a Mann–Whitney test (p < 0.05), there is a significant difference in microplastic abundance between areas subjected to different levels of human activity. Corals showed the highest concentration of microplastics, with fragments being the most dominant type. No significant difference in microplastic abundance was found among the different polyp sizes (Mann–Whitney test, p > 0.05) or among different species (Kruskal–Wallis test, p > 0.05). All coral samples contained fragment and fiber microplastics in their polyps, consisting of Polyethylene terephthalate (PET), silicone-based plastic, polysulfoxide, and Polyvinyl alcohol (PVA) polymer. Here, we provide the first evidence of microplastics inside corals, observed using a histological method. The types of microplastic detected in the histological sections were similar to those extracted from the coral polyps. Tourism and fishing activity both play a role in governing the distribution, abundance, and diversity of microplastics in coral reef systems.

Establishment of oxidative stress biomarkers in oocytes from healthy and bleached scleractinian corals

Corals have a symbiotic relationship with photosynthetic dinoflagellates associated with the host's tissue, those responsible for most of their daily energy gain. Warming ocean water breaks down symbiosis, leading to a phenomenon known as bleaching. Without their primary nutritional source, corals depend on heterotrophy to survive, which can stagnate the reproductive cycle. There are corals, however, that manage to maintain gametogenesis even when bleached. However, the physiology of these gametes in such a situation is unknown. Our study is the first to evaluate the effects of bleaching on the oocytes of a scleractinian coral, as well as the strategies of these cells to maintain the balance of the antioxidant system and cellular homeostasis. We evaluated and quantified markers of oxidative balance in oocytes released from colonies of Mussismilia harttii with different physiological conditions: bleached and healthy. Healthy and bleached coral oocytes were collected considering a post-spawning time curve (0, 5 and 10 h) and frozen to evaluate the relationship between oxidative balance markers and the physiological conditions of coral colonies. Total protein levels, the activity of the antioxidants superoxide dismutase (SOD) and catalase (CAT), and the levels of lipoperoxidation (TBARS), a marker of lipid damage, were measured. The oocytes presented a significant difference between 0 h and 5 h after spawning for all the parameters regardless of the colony's health. Health status modulated SOD activity and TBARS levels, with oocytes from the bleached colony suffering the most lipid damage. These organisms seem to preserve the quality of female gametic cells even 10 h after spawning in both colonies, suggesting a robust antioxidant system capable of prolonging their lifespan and, possibly, their fertilization capability. This response may be related to an intensification of heterotrophy, ensuring nutritional support and thus reproductive effort and quality of gametes even in bleached corals.

Location assessment for coral reef transplantation program in Karawang Waters, Indonesia

Environmental degradation caused by anthropogenic activities and climate change has an impact on the habitat of organisms and biodiversity. Coral reefs are one of the sensitive ecosystems that are strongly influenced by environmental changes. Poor environmental conditions in the Java Sea and global warming are the main factors that affect the sustainability of coral reef ecosystems in Karawang waters. Coral reef transplantation is a method that has long been used to revitalize coral reef ecosystems. This study aims to assess the ideal location used for coral reef transplantation program in Karawang Waters. Through a field survey, the percentage of coral reef cover, dead coral, hard coral, algae, and biotic and abiotic components at several sampling points in 2019 to 2022 was obtained. The sampling location with the poor conditions are considered to be used as transplant locations. Based on analysis result, only 1 out of 3 locations that are suitable to be used as locations for coral reef transplantation programs.

Heat-evolved algal symbionts enhance bleaching tolerance of adult corals without trade-off against growth.

Ocean warming has caused coral mass bleaching and mortality worldwide and the persistence of symbiotic reef-building corals requires rapid acclimation or adaptation. Experimental evolution of the coral's microalgal symbionts followed by their introduction into coral is one potential method to enhance coral thermotolerance. Heat-evolved microalgal symbionts of the generalist species, Cladocopium proliferum (strain SS8), were exposed to elevated temperature (31°C) for ~10 years, and were introduced into four genotypes of chemically bleached adult fragments of the scleractinian coral, Galaxea fascicularis. Two of the four coral genotypes acquired SS8. The new symbionts persisted for the 5 months of the experiment and enhanced adult coral thermotolerance, compared with corals that were inoculated with the wild-type C. proliferum strain. Thermotolerance of SS8-corals was similar to that of coral fragments from the same colony hosting the homologous symbiont, Durusdinium sp., which is naturally heat tolerant. However, SS8-coral fragments exhibited faster growth and recovered cell density and photochemical efficiency more quickly following chemical bleaching and inoculation under ambient temperature relative to Durusdinium-corals. Mass spectrometry imaging suggests that algal pigments involved in photobiology and oxidative stress were the greatest contributors to the thermotolerance differences between coral hosting heat-evolved versus wild-type C. proliferum. These pigments may have increased photoprotection in the heat-evolved symbionts. This is the first laboratory study to show that thermotolerance of adult corals (G. fascicularis) can be enhanced via the uptake of exogenously supplied, heat-evolved symbionts, without a trade-off against growth under ambient temperature. Importantly, heat-evolved C. proliferum remained in the corals in moderate abundance 2 years after first inoculation, suggesting long-term stability of this novel symbiosis and potential long-term benefits to coral thermotolerance.

Chemical diversity of scleractinian corals revealed by untargeted metabolomics and molecular networking

Chemical diversity of scleractinian corals revealed by untargeted metabolomics and molecular networking

Filamentous virus-like particles are present in coral dinoflagellates across genera and ocean basins

Filamentous viruses are hypothesized to play a role in stony coral tissue loss disease (SCTLD) through infection of the endosymbiotic dinoflagellates (Family Symbiodiniaceae) of corals. To evaluate this hypothesis, it is critical to understand the global distribution of filamentous virus infections across the genetic diversity of Symbiodiniaceae hosts. Using transmission electron microscopy, we demonstrate that filamentous virus-like particles (VLPs) are present in over 60% of Symbiodiniaceae cells (genus Cladocopium) within Pacific corals (Acropora hyacinthus, Porites c.f. lobata); these VLPs are more prevalent in Symbiodiniaceae of in situ colonies experiencing heat stress. Symbiodiniaceae expelled from A. hyacinthus also contain filamentous VLPs, and these cells are more degraded than their in hospite counterparts. Similar to VLPs reported from SCTLD-affected Caribbean reefs, VLPs range from ~150 to 1500 nm in length and 16–37 nm in diameter and appear to constitute various stages in a replication cycle. Finally, we demonstrate that SCTLD-affected corals containing filamentous VLPs are dominated by diverse Symbiodiniaceae lineages from the genera Breviolum, Cladocopium, and Durusdinium. Although this study cannot definitively confirm or refute the role of filamentous VLPs in SCTLD, it demonstrates that filamentous VLPs are not solely observed in SCTLD-affected corals or reef regions, nor are they solely associated with corals dominated by members of a particular Symbiodiniaceae genus. We hypothesize that filamentous viruses are a widespread, common group that infects Symbiodiniaceae. Genomic characterization of these viruses and empirical tests of the impacts of filamentous virus infection on Symbiodiniaceae and coral colonies should be prioritized.

Microfacies Analysis of the Reefal Limestone, Marah Formation, East Borneo, Indonesia

Miau Baru, Kongbeng in East Borneo is a relatively narrow area with complex geological features. The abundance of larger benthic foraminifera shows diversity in the carbonate succession of the Marah Formation but previously has less attention from microfacies perspective. To achieve the objective in this microfacies analysis of the reefal limestone of Priabonian-Aquitanian. Marah Formation, limestone samples were collected and sectioned. A total of 35 samples were selected, 25 from the Goa Indah section and 10 from the Kongbeng section. The assemblage of larger benthic foraminifera was recorded to help determine the depositional age, and biota of the formation and to interpret the facies zone. Field observation, microfacies type, as well as the fossil content of larger benthic foraminifera and colonial scleractinian corals indicated that the deposition of the Marah Formation in the Miau Baru area probably ranged from open circulation shallow forereef to backreef shelf.

Contact-free impacts of sessile reef organisms on stony coral productivity

Coral reefs are biodiversity and productivity hotspots where space limitation makes interactions between organisms inevitable. Biodiversity loss alters these interactions, however downstream effects on the productivity of individual species remain unexplored. Here, we quantified immediate and long-term changes in stony coral productivity in response to contact-free interactions with various benthic organisms (stony corals, soft corals, macroalgae, sponges). We show that corals sense the presence of other organisms and subsequently modulate their productivity. Each stony coral species had a characteristic reaction to contact-free stimuli, while the identity of the interaction partner was of subordinate importance. Our data highlight downstream effects that biodiversity loss and shifting coral reef communities may have through indirect modulation of productivity, resulting in uneven effects among species. The productivity response is probably mediated by secondary metabolites released into the water. The underlying communication pathways that mediate these interactions remain to be investigated.

Coral reefs in the northeastern Saudi Arabian Red Sea are resilient to mass coral mortality events

We conducted an integrated survey combining visual census and baited remote underwater video survey on the coral reefs in the northeastern Red Sea and examined their health by comparing the baseline information from two decades ago. The mean coverage of the corals of all stations was 36 %, including 32 % stony corals and 4.0 % soft corals, significantly higher and lower to previous baseline. Observed high proportion of dead corals indicated the occurrence of the events of mass mortality, and the heating events were the most likely cause. Similar levels of coral coverage compared to two decades ago indicated their resilience to past events with mass coral mortality. Small proportions of macroalgae and sea urchins indicated that they might be controlled by their predators frequently observed in both visual census and underwater video survey. Regular monitoring and careful development plans are needed to safeguard these invaluable reefs.