Endangered Coral Research Articles

Hybridization and inbreeding affect the survival of a critically endangered coral.

Coral reefs face escalating pressures leading to unprecedented declines in the populations of reef-building corals.1,2 Conservation genomic studies are critical in understanding and formulating interventions to reverse such declines but thus far have only focused on a handful of broadcast-spawning species in shallow waters.3,4 The recent International Union for Conservation of Nature (IUCN) reclassification of six different brooding corals as "critically endangered"5 indicates that such species are equally threatened. However, we lack a thorough understanding of the factors underlying their decline. Here, we comprehensively examine the genetic impacts of a severe population decline in the brooding coral Helioseris cucullata, once a major contributor to Caribbean reefs but now critically endangered.6,7,8 Genome-wide sequencing of colonies across five locations revealed the presence of two distinct species, indicating that the remaining population sizes are even smaller than previously estimated. Using an exhaustive, spatially explicit sampling approach (across a total of ∼2.5 hectares), we observed extremely low genetic diversity and identified how localized dispersal, excessive inbreeding, and prevalent asexual reproduction may contribute to an extinction vortex. However, we also found evidence for recent hybridization and introgression, providing an avenue for the reintroduction of genetic diversity into both lineages. With many brooding species now under threat, these results highlight the critical need to assess the genetic processes associated with their declines so that these can be harnessed or mitigated to deliver effective conservation outcomes.

Genomes of the Caribbean reef-building corals Colpophyllia natans, Dendrogyra cylindrus, and Siderastrea siderea.

Corals populations worldwide are declining rapidly due to elevated ocean temperatures and other human impacts. The Caribbean harbors a high number of threatened, endangered, and critically endangered coral species compared to reefs of the larger Indo-Pacific. The reef corals of the Caribbean are also long diverged from their Pacific counterparts and may have evolved different survival strategies. Most genomic resources have been developed for Pacific coral species which may impede our ability to study the changes in genetic composition of Caribbean reef communities in response to global change. To help fill the gap in genomic resources, we used PacBio HiFi sequencing to generate the first genome assemblies for three Caribbean, reef-building corals, Colpophyllia natans, Dendrogyra cylindrus, and Siderastrea siderea. We also explore the genomic novelties that shape scleractinian genomes. Notably, we find abundant gene duplications of all classes (e.g., tandem and segmental), especially in S. siderea. This species has one of the largest genomes of any scleractinian coral (822Mb) which seems to be driven by repetitive content and gene family expansion and diversification. As the genome size of S. siderea was double the size expected of stony corals, we also evaluated the possibility of an ancient whole genome duplication using Ks tests and found no evidence of such an event in the species. By presenting these genome assemblies, we hope to develop a better understanding of coral evolution as a whole and to enable researchers to further investigate the population genetics and diversity of these three species.

Stronger Hurricanes and Climate Change in the Caribbean Sea: Threats to the Sustainability of Endangered Coral Species

An increasing sea surface temperature as a result of climate change has led to a higher frequency and strengthening of hurricanes across the northeastern Caribbean in recent decades, with increasing risks of impacts to endangered corals and to the sustainability of coral reefs. Category five Hurricanes Irma and María during 2017 caused unprecedented damage to coral reef ecosystems across northeastern Puerto Rico, including mechanical destruction, localized sediment bedload (horizontal sediment transport and abrasion), and burial by hurricane-generated rubble fields. Hurricanes inflicted significant site-, depth-, and life history trait-specific impacts to endangered corals, with substantial and widespread mechanical damage to branching species, moderate mechanical damage to foliose species, and moderate to high localized damage to small-sized encrusting and massive morphotypes due to sediment bedload and burial by rubble. There was a mean 35% decline in Acropora palmata live cover, 79% in A. cervicornis, 12% in Orbicella annularis, 7% in O. faveolata, 12% in O. franksi, and 96% in Dendrogyra cylindrus. Hurricane disturbances resulted in a major regime shift favoring dominance by macroalgae, algal turf, and cyanobacteria. Recovery from coral recruitment or fragment reattachment in A. palmata was significantly higher on more distant coral reefs, but there was none for massive endangered species. Stronger hurricanes under projected climate change may represent a major threat to the conservation of endangered coral species and reef sustainability which will require enhancing coral propagation and restoration strategies, and the integration of adaptive, ecosystem-based management approaches. Recommendations are discussed to enhance redundancy, rapid restoration responses, and conservation-oriented strategies.

The application and sustainable development of coral in traditional medicine and its chemical composition, pharmacology, toxicology, and clinical research.

This review discusses the variety, chemical composition, pharmacological effects, toxicology, and clinical research of corals used in traditional medicine in the past twodecades. At present, several types of medicinal coral resources are identified, which are used in 56 formulas such as traditional Chinese medicine, Tibetan medicine, Mongolian medicine, and Uyghur medicine. A total of 34 families and 99 genera of corals are involved in medical research, with the Alcyoniidae family and Sarcophyton genus being the main research objects. Based on the structural types of compounds and the families and genera of corals, this review summarizes the compounds primarily reported during the period, including terpenoids, steroids, nitrogen-containing compounds, and other terpenoids dominated by sesquiterpene and diterpenes. The biological activities of coral include cytotoxicity (antitumor and anticancer), anti-inflammatory, analgesic, antibacterial, antiviral, immunosuppressive, antioxidant, and neurological properties, and a detailed summary of the mechanisms underlying these activities or related targets is provided. Coral toxicity mostly occurs in the marine ornamental soft coral Zoanthidae family, with palytoxin as the main toxic compound. In addition, nonpeptide neurotoxins are extracted from aquatic corals. The compatibility of coral-related preparations did not show significant acute toxicity, but if used for a long time, it will still cause toxicity to the liver, kidneys, lungs, and other internal organs in a dose-dependent manner. In clinical applications, individual application of coral is often used as a substitute for orthopedic materials to treat diseases such as bone defects and bone hyperplasia. Second, coral is primarily available in the form of compound preparations, such as Ershiwuwei Shanhu pills and Shanhu Qishiwei pills, which are widely used in the treatment of neurological diseases such as migraine, primary headache, epilepsy, cerebral infarction, hypertension, and other cardiovascular and cerebrovascular diseases. It is undeniable that the effectiveness of coral research has exacerbated the endangered status of corals. Therefore, there should be no distinction between the advantages and disadvantages of listed endangered species, and it is imperative to completely prohibit their use and provide equal protection to help them recover to their normal numbers. This article can provide some reference for research on coral chemical composition, biological activity, chemical ecology, and the discovery of marine drug lead compounds. At the same time, it calls for people to protect endangered corals from the perspectives of prohibition, substitution, and synthesis.

Environmental predictors for the restoration of a critically endangered coral, Acropora palmata, along the Florida reef tract.

The population decline and lack of natural recovery of multiple coral species along the Florida reef tract have instigated the expanding application of coral restoration and conservation efforts. Few studies, however, have determined the optimal locations for the survival of outplanted coral colonies from restoration nurseries. This study predicts the optimal locations for Acropora palmata colonies along the Florida reef tract using a boosted-regression-tree model to examine the relationships between the occurrence of wild A. palmata and ten environmental variables. Our model results predicted A. palmata was most likely to occur in shallow reef habitats with (i) generally low mean chlorophyll-a concentrations (< 1 mg m-3), (ii) moderate fetch (3 kJ m-2), (iii) salinities between 20 and 37.5 ppt, (iv) temperatures between 20 and 32°C, (vi) low mean concentrations of total nitrogen (0.16 ppm), and (iv) irradiance between 26.5 and 53.5 mol m-2 s-1. The most suitable habitats for A. palmata were disproportionately allocated to reefs in Biscayne Bay, the Upper Keys, the western-lower Florida Keys, the Marquesas, and the Dry Tortugas. The middle Florida Keys had unfavorable environmental conditions for A. palmata habitat. Results from this study inform where A. palmata, outplanted as part of restoration and conservation efforts, would have suitable environmental conditions to persist over time. This study also provides decision-making support for management focused on the conservation and restoration of the endangered species A. palmata along the Florida reef tract.

Exposure to global change and microplastics elicits an immune response in an endangered coral

Global change is increasing seawater temperatures and decreasing oceanic pH, driving declines of coral reefs globally. Coral ecosystems are also impacted by local stressors, including microplastics, which are ubiquitous on reefs. While the independent effects of these global and local stressors are well-documented, their interactions remain less explored. Here, we examine the independent and combined effects of global change (ocean warming and acidification) and microplastics exposures on gene expression (GE) and microbial community composition in the endangered coral Acropora cervicornis. Nine genotypes were fragmented and maintained in one of four experimental treatments: 1) ambient conditions (ambient seawater, no microplastics; AMB); 2) microplastics treatment (ambient seawater, microplastics; MP); 3) global change conditions (warm and acidic conditions, no microplastics; OAW); and 4) multistressor treatment (warm and acidic conditions with microplastics; OAW+MP) for 22 days, after which corals were sampled for genome-wide GE profiling and ITS2 and 16S metabarcoding. Overall A. cervicornis GE responses to all treatments were subtle; however, corals in the multistressor treatment exhibited the strongest GE responses, and genes associated with innate immunity were overrepresented in this treatment. ITS2 analyses confirmed that all coral were associated with Symbiodinium ‘fitti’ and 16S analyses revealed similar microbiomes dominated by the bacterial associate Aquarickettsia, suggesting that these A. cervicornis fragments exhibited remarkably low variability in algal and bacterial community compositions. Future work should focus on functional differences across microbiomes, especially Aquarickettsia and viruses, in these responses. Overall, results suggest that when local stressors are coupled with global change, these interacting stressors present unique challenges to this endangered coral species.

Distribution, abundance, and health indicators of the critically endangered coral species Acropora cervicornis in Los Roques National Park, 2014

Acropora cervicornis is one of the most important coral species in shallow reefs of the Caribbean as it provides habitat and structural complexity to several species of invertebrates and fish. However, the distribution range of A. cervicornis has shrunk and collapsed considerably during the last five decades, due to a combination of factors including the increase of disease prevalence, storm frequency, and anthropogenic threats. Despite being classed as “Critically Endangered” in the IUCN Red List, information regarding its population status and condition across large Caribbean coralline areas is limited. Herein we conducted the first Marine Protected Area (MPA) scale survey for this species at the Los Roques archipelago, which included visual census across 127 sites to determine the abundance, spatial distribution, habitat type (i.e., leeward, windward), and patch morphology of A. cervicornis (i.e., continuous, dispersed, scatter, isolated). We selected 11 sites, where this species was predicted and reported to be ubiquitous, to determine live A. cervicornis cover, its recent and old mortality cover, and white band disease prevalence as proxies for coral health. For this, four 25-m long photomosaics were analysed at each site. We found Acropora cervicornis in only 29% of the surveyed sites; indicating that this species currently has a narrow and very restricted distribution in Los Roques and suggesting that either this species is rare or has declined over the past decades within the MPA. Dispersed and scattered patches prevailed upon continuous patches, which only occurred in two of the surveyed sites. Moreover, these patches were located near the largest human population settlements, and inside the low protection zones of the MPA where fishing and touristic activities are permitted. The photomosaic survey showed that more than 75% A. cervicornis patches showed an average live cover above 27%, low prevalence of white band disease (&lt;7%), and low macroalgal abundance (&lt;10%); suggesting that Los Roques still holds healthy populations. Our results indicate that the persistence of this species urgently requires re-evaluating current MPA zoning, especially following recent evidence of overfishing and inadequate law enforcement. This study provides a baseline of A. cervicornis populations in Los Roques and Southern Caribbean that can be later used for local population management and conservation.

Assisted gene flow using cryopreserved sperm in critically endangered coral

Assisted gene flow (AGF) is a conservation intervention to accelerate species adaptation to climate change by importing genetic diversity into at-risk populations. Corals exemplify both the need for AGF and its technical challenges; corals have declined in abundance, suffered pervasive reproductive failures, and struggled to adapt to climate change, yet mature corals cannot be easily moved for breeding, and coral gametes lose viability within hours. Here, we report the successful demonstration of AGF in corals using cryopreserved sperm that was frozen for 2 to 10 y. We fertilized Acropora palmata eggs from the western Caribbean (Curaçao) with cryopreserved sperm from genetically distinct populations in the eastern and central Caribbean (Florida and Puerto Rico, respectively). We then confirmed interpopulation parentage in the Curaçao-Florida offspring using 19,696 single-nucleotide polymorphism markers. Thus, we provide evidence of reproductive compatibility of a Caribbean coral across a recognized barrier to gene flow. The 6-mo survival of AGF offspring was 42%, the highest ever achieved in this species, yielding the largest wildlife population ever raised from cryopreserved material. By breeding a critically endangered coral across its range without moving adults, we show that AGF using cryopreservation is a viable conservation tool to increase genetic diversity in threatened marine populations.

Estimating high-resolution Red Sea surface temperature hotspots, using a low-rank semiparametric spatial model

In this work, we estimate extreme sea surface temperature (SST) hotspots, that is, high threshold exceedance regions, for the Red Sea, a vital region of high biodiversity. We analyze high-resolution satellite-derived SST data comprising daily measurements at 16,703 grid cells across the Red Sea over the period 1985–2015. We propose a semiparametric Bayesian spatial mixed-effects linear model with a flexible mean structure to capture spatially-varying trend and seasonality, while the residual spatial variability is modeled through a Dirichlet process mixture (DPM) of low-rank spatial Student’s t processes (LTPs). By specifying cluster-specific parameters for each LTP mixture component, the bulk of the SST residuals influence tail inference and hotspot estimation only moderately. Our proposed model has a nonstationary mean, covariance, and tail dependence, and posterior inference can be drawn efficiently through Gibbs sampling. In our application, we show that the proposed method outperforms some natural parametric and semiparametric alternatives. Moreover, we show how hotspots can be identified, and we estimate extreme SST hotspots for the whole Red Sea, projected until the year 2100, based on the Representative Concentration Pathways 4.5 and 8.5. The estimated 95% credible region, for joint high threshold exceedances include large areas covering major endangered coral reefs in the southern Red Sea.

Effects of herbivory by the urchin Diadema antillarum on early restoration success of the coral Acropora cervicornis in the central Caribbean

In an era of coral reef decline, coral restoration is receiving increasing attention, with many recent developments in culture and transplant techniques. However, how the ecological processes operating on coral reefs influence the success of restoration efforts remains largely unexplored, particularly during the first months after outplanting which are considered crucial for colony survival. Herbivory is a key process well-known to maintain a coral-dominated state, and in the Caribbean Sea, the long-spine urchin Diadema antillarum is thought to aid coral success by removing algae from seafloor substrate that might otherwise outcompete coral outplants. In this study, we conducted a three-month manipulative experiment in southeastern Dominican Republic to test the effect of Diadema antillarum density on percent living tissue and growth rate of outplanted fragments of the critically endangered coral species Acropora cervicornis. Increasing herbivore density had no significant effect on coral survival or growth but did increase the percent of living tissue when urchin abundance was 3× ambient levels. The greatest growth and survival outcomes were instead related to the initial size of the outplanted coral and were reduced through predation by the fireworm Hermodice carunculata. Our results highlight the potential importance of considering ecological processes like herbivory and predation to maximize the success of ecological restoration.

Mitigation of coral ecosystem service-related social issues: evidence from a coastal development project in a developing country

ABSTRACT Biodiversity offset, with a focus on securing biological validity, is primarily practiced in developed countries. However, various social issues, such as the tradeoff between ecosystem conservation and the use of ecosystem services, have arisen and require attention. To address these issues, this study proposes an approach applicable at the planning stages of coral offsetting. We propose a comparison of the relationship between social characteristics and coral ecosystem services across offset candidate sites, suggest an analysis of restorability and the extent of human dependency on coral ecosystem services as part of the process of selecting an offset site, and confirm the practicability of our approach for a specific case of coral offsetting in a developing country. The results reveal that all candidate sites (even across a small area) have advantages and disadvantages regarding the mitigation of social issues. We further discuss the implications of these results with respect to the sustainable usage of endangered corals.

Spatial distribution of microbial communities among colonies and genotypes in nursery-reared Acropora cervicornis.

BackgroundThe architecturally important coral species Acropora cervicornis and A. palmata were historically common in the Caribbean, but have declined precipitously since the early 1980s. Substantial resources are currently being dedicated to coral gardening and the subsequent outplanting of asexually reproduced colonies of Acropora, activities that provide abundant biomass for both restoration efforts and for experimental studies to better understand the ecology of these critically endangered coral species.MethodsWe characterized the bacterial and archaeal community composition of A. cervicornis corals in a Caribbean nursery to determine the heterogeneity of the microbiome within and among colonies. Samples were taken from three distinct locations (basal branch, intermediate branch, and branch tip) from colonies of three different coral genotypes.ResultsOverall, microbial community composition was similar among colonies due to high relative abundances of the Rickettsiales genus MD3-55 (Candidatus Aquarickettsia) in nearly all samples. While microbial communities were not different among locations within the same colony, they were significantly different between coral genotypes. These findings suggest that sampling from any one location on a coral host is likely to provide a representative sample of the microbial community for the entire colony. Our results also suggest that subtle differences in microbiome composition may be influenced by the coral host, where different coral genotypes host slightly different microbiomes. Finally, this study provides baseline data for future studies seeking to understand the microbiome of nursery-reared A. cervicornis and its roles in coral health, adaptability, and resilience.

First Records for Spawning of Caribbean Acropora Species in Colombian MPAs

Estimates of Colombian Caribbean coral percent cover in the Southern Caribbean are consistent with those throughout the Caribbean Sea, which has declined to about 10% of historical levels in the last few decades. Human activities like destructive fishing techniques in the marine parks have degraded the reefs over the last few decades. Colombia’s Marine Protected Areas (MPAs) have thousands of square kilometers to map and patrol and few resources to devote to scientific and restoration efforts. Efforts to implement sexual reproduction techniques for restoration are starting to successfully propagate and settle corals on ceramic plates for reef deployment in the area but require more natural history information for large-scale implementation in restoration. Past observations of captive endangered coral Acropora cervicornis in the nursery of the Oceanario Islas del Rosario indicate spawning 6 days after the August full moon for the previous 3 years. Coral spawn collection from the wild reef was completed each night from 2 to 7 days after the full moon in August 2019, and resulted in the first observation of A. cervicornis spawning on natural reefs in Parque Nacional Natural Los Corales del Rosario y de San Bernardo, a 1,200 km2 underwater national park and MPA established in 1977. Additionally, coral spawn collection from the nursery reefs in August 2019 provide the first reported observations of spawning for endangered coral Acropora palmata in Colombia.

Geographic distances and ocean currents influence Caribbean Acropora palmata population connectivity in the Lesser Antilles

The critically endangered coral species Acropora palmata used to dominate shallow Caribbean reefs but since the early 1980s, populations have dramatically declined. At the Caribbean scale, A. palmata is divided into two genetically divergent lineages and most of previous works investigating population connectivity among populations involved the western lineage (in Florida, the Bahamas, the Mesoamerican Reef System, and the Greater Antilles). Small scale genetic connectivity among A. palmata populations was globally found, possibly enhancing populations’ recovery at the local scale. Yet, little is known regarding the genetic connectivity of populations of the eastern lineage, especially those of the Lesser Antilles, a fragmented archipelago located at the edge of the species distribution. Here, we filled this gap by investigating the genetic diversity, population structure and connectivity of A. palmata populations among 36 sampled sites from 11 islands of the Lesser Antilles using 14 hypervariable microsatellite loci. Globally, genetic diversity levels in A. palmata populations from the Lesser Antilles were lower compared to what was previously reported within the Wider Caribbean. The analysis of the genetic structure, crossed with spatial autocorrelation analysis, revealed an isolation-by-distance pattern at both reef and Lesser Antilles scales. A gene dispersal distance of less than a kilometer, and a northward gene flow direction, in agreement with ocean surface currents in the region were found. Altogether, our results suggest a restricted population connectivity and short distance dispersal of A. palmata larvae within the Lesser Antilles further limited by geographic distances among suitable habitat patches. Additionally, our results suggest that southernmost populations are potential sources of larvae for the most northerly islands and have a key role in reseeding A. palmata populations of the Lesser Antilles.

First look into the venom of Roatan Island's critically endangered coral snake Micrurus ruatanus: Proteomic characterization, toxicity, immunorecognition and neutralization by an antivenom

A proteomic and toxicological study of the venom from one specimen of Micrurus ruatanus, a critically endangered coral snake species endemic to Roatan Island, Honduras, was carried out. Immunorecognition and neutralization of venom lethality by an anticoral antivenom was also evaluated. Forty peaks were collected from RP-HPLC fractionation of the venom. After SDS-PAGE analysis, fifty-eight bands were examined by MALDI-TOF/TOF mass spectrometry. Micrurus ruatanus venom displayed a three-finger toxin (3FTx)-rich venom phenotype, as well as a significant amount of phospholipases A2 (PLA2s). Various other proteins were identified, including Kunitz-type inhibitor proteins, L-amino acid oxidases, C-type lectin/lectin-like, metalloproteinases, serine proteinases, vespryn/ohanin, 5′-nucleotidases, glutathione peroxidases, and phosphodiesterases. Micrurus ruatanus venom displayed significant PLA2 activity in vitro and myotoxicity in vivo. The venom showed high lethal potency in mice, being one of the most lethal in Central America. The anticoral antivenom (SAC-ICP) produced by Instituto Clodomiro Picado neutralized the lethal activity of the venom. Major fractions with relevant lethal activity were also identified by a screening analysis. SignificanceThe proteomic characterization, toxicity, immunorecognition and neutralization of Micrurus ruatanus venom have been determined for the first time. This coral snake is endemic to Roatan Island and contains a three-finger toxin-rich venom that displayed a potent lethal activity in mice. The anticoral antivenom produced by Instituto Clodomiro Picado neutralized the lethal activity of this venom in vivo, and therefore should be effective in the treatment of envenomings by this snake.

Spawning aggregations act as a bottleneck influencing climate change impacts on a critically endangered reef fish

AbstractAimMost projections of how climate change will affect species distributions and phenology are based on a species’ most conspicuous life stage. However, not all life stages are equally sensitive to temperature. Among fishes, spawning adults often have narrower thermal tolerances than other life stages and may constrain population responses to climate change. We tested this hypothesis using data on Nassau Grouper (Epinephelus striatus), an endangered coral reef fish.LocationGreater Caribbean.MethodsSpecies distribution models of spawning and nonspawning adults were compared to determine which environmental variables exerted the greatest influence on grouper distribution. We calculated the thermal niche and ecological niche breadth of both life stages. An earth system model was applied to project how species distribution and phenology shift under two climate change scenarios.ResultsSea surface temperature and seasonal temperature gradients affected the distribution of both spawning and nonspawning adults, but these life stages differed in their preferred temperatures and reaction to oceanic currents. While the two life stages exhibited similar ecological niche breadth, the thermal niche of spawners was narrower. By 2081–2100, potential spawning habitat was projected to decline under a business‐as‐usual scenario by 82% relative to 1981–2000, whereas suitable habitat for nonspawners decreased by 46%. Poleward shifts in latitude occurred 3.8–4.2 times faster for spawners than nonspawners. These changes were attributed to rising temperatures, whereas hydrographical changes did not have a substantial impact. Spawning phenology changed little, with a slight contraction in spawning season but a large reduction in spawning probability across all months.Main ConclusionsA narrow thermal tolerance range among spawning fishes indicates that this life stage may be a bottleneck constraining responses to climate change. Future research should consider the reaction of each life stage to changing conditions. Conservation of E. striatus should take shifting distribution and phenology into account, as climate effects may exacerbate population declines due to fishing and reduce the efficacy of conservation measures.

High genetic diversity and limited genetic connectivity in 2 populations of an endemic and endangered coral species: Porites sverdrupi

The coral Porites sverdrupi is the only scleractinian endemic to the Gulf of California. Over the last 2 decades its populations have been restricted to 3 areas, La Paz Bay, Loreto Bay, and Concepción Bay. As this species faces a high risk of extinction, there is an urgent need for biological, ecological, and genetic information for the guidance of conservation efforts. This is the first study on genetic diversity and connectivity in the species. For this, we analyzed coral colonies from Loreto Bay and Concepción Bay. Our results show that there is high genetic diversity in P. sverdrupi at both sites, with significant genetic structure between them. This condition is caused by a combination of short pelagic larval duration, low dispersal potential between the populations, and local adaptation. Our results emphasize the need for more research in order to establish adequate conservation strategies.

Extensive transcriptional variation poses a challenge to thermal stress biomarker development for endangered corals.

As climate changes, sea surface temperature anomalies that negatively impact coral reef organisms continue to increase in frequency and intensity. Yet, despite widespread coral mortality, genetic diversity remains high even in those coral species listed as threatened. While this is good news in many ways, it presents a challenge for the development of biomarkers that can identify resilient or vulnerable genotypes. Taking advantage of three coral restoration nurseries in Florida that serve as long-term common garden experiments, we exposed over 30 genetically distinct Acropora cervicornis colonies to hot and cold temperature shocks seasonally and measured pooled gene expression responses using RNAseq. Targeting a subset of 20 genes, we designed a high-throughput qPCR array to quantify expression in all individuals separately under each treatment with the goal of identifying predictive and/or diagnostic thermal stress biomarkers. We observed extensive transcriptional variation in the population, suggesting abundant raw material is available for adaptation via natural selection. However, this high variation made it difficult to correlate gene expression changes with colony performance metrics such as growth, mortality and bleaching susceptibility. Nevertheless, we identified several promising diagnostic biomarkers for acute thermal stress that may improve coral restoration and climate change mitigation efforts in the future.

A conserved Toll-like receptor-to-NF-κB signaling pathway in the endangered coral Orbicella faveolata

Herein, we characterize the Toll-like receptor (TLR)-to-NF-κB innate immune pathway of Orbicella faveolata (Of), which is an ecologically important, disease-susceptible, reef-building coral. As compared to human TLRs, the intracellular TIR domain of Of-TLR is most similar to TLR4, and it can interact in vitro with the human TLR4 adapter MYD88. Treatment of O. faveolata tissue with lipopolysaccharide, a ligand for mammalian TLR4, resulted in gene expression changes consistent with NF-κB pathway mobilization. Biochemical and cell-based assays revealed that Of-NF-κB resembles the mammalian non-canonical NF-κB protein p100 in that C-terminal truncation results in translocation of Of-NF-κB to the nucleus and increases its DNA-binding and transcriptional activation activities. Moreover, human IκB kinase (IKK) and Of-IKK can both phosphorylate conserved residues in Of-NF-κB in vitro and induce C-terminal processing of Of-NF-κB in vivo. These results are the first characterization of TLR-to-NF-κB signaling proteins in an endangered coral, and suggest that these corals have conserved innate immune pathways.

Endangered New Caledonian endemic mushroom coral Cantharellus noumeae in turbid, metal-rich, natural and artificial environments

Since its description in 1984, little attention has been paid to the New Caledonian endemic mushroom coral Cantharellus noumeae (Fungiidae), an IUCN Red-listed, endangered coral species. Our study presents the first ever quantitative assessment conducted on C. noumeae populations for two contrasting sites in the same turbid bay. Sites differed by their substrates of artificial or natural origins. Metal concentrations of superficial sediment were measured. C. noumeae was found in high densities in metal-rich and turbid environments at both locations, reaching up to 288 individuals per 50m2. It was 3.5 times more abundant on natural rock than on artificial substrates. Recruitment was also higher proportionally on rock (47% vs 7–14%). The composition of the associated coral communities included 30–37 species occurring in low densities. Our findings clarify the environmental niche of this species and its colonization potential, in order to eventually better characterize its conservation status.