Scleractinian Corals Research Articles

Beaks Promote Rapid Morphological Diversification Along Distinct Evolutionary Trajectories in Labrid Fishes (Eupercaria: Labridae).

The upper and lower jaws of some wrasses (Eupercaria: Labridae) possess teeth that have been coalesced into a strong durable beak that they use to graze on hard coral skeletons, hard-shelled prey, and algae, allowing many of these species to function as important ecosystem engineers in their respective marine habitats. While the ecological impact of the beak is well-understood, questions remain about its evolutionary history and the effects of this innovation on the downstream patterns of morphological evolution. Here we analyze 3D cranial shape data in a phylogenetic comparative framework and use paleoclimate modeling to reconstruct the evolution of the labrid beak across 205 species. We find that wrasses evolved beaks three times independently, once within odacines, and twice within parrotfishes in the Pacific and Atlantic Oceans. We find an increase in the rate of shape evolution in the Scarus+Chlorurus+Hipposcarus (SCH) clade of parrotfishes likely driven by the evolution of the intramandibular joint. Paleoclimate modeling shows that the SCH clade of parrotfishes rapidly morphologically diversified during the middle Miocene. We hypothesize that possession of a beak in the SCH clade coupled with favorable environmental conditions allowed these species to rapidly morphologically diversify.

Biodiversity, ecology, and taxonomy of sediment-dwelling Dendrophylliidae (Anthozoa, Scleractinia) in the Gulf of Thailand

Abstract Dendrophylliidae represents one of the most speciose families of scleractinian coral, expressing a wide range of morphological and ecological traits. Recent phylogenetic analyses of the family have indicated that several conventional genera are in need of revision. In the Gulf of Thailand, dendrophylliids are predominantly found on hard-substrate reefs and pinnacles, or on soft-substrate habitats. Soft-substrate habitats in the Gulf of Thailand have been shown to host unique species assemblages and faunal ecology. Here we provided an updated phylogenetic hypothesis for the Dendrophylliidae based on newly sequenced species, and analyses integrating morphology, genetics and ecology. High-resolution Micro-ct was used to create digital versions of the studied species, allowing for non-destructive examination of internal and external features. Our findings allowed for a taxonomic assessment of the genera Heteropsammia and Tubastraea, with the species Balanophyllia (Eupsammia) stimpsonii, moved to the genus Tubastraea. They also support the polyphyly of Dendrophyllia and Cladopsammia. In-situ surveys provided population-density information for four dendrophylliid species from soft substrate habitats, indicating that the species Heteropsammia moretonensis may be the most widespread within the Gulf of Thailand. These surveys also provided novel ecological documentation associated with these corals, including protocooperative feeding upon a sea pen by Tubastraea stimpsonii comb. nov., and feeding upon other cnidarians by Heteropsammia spp.

A hybrid-capture approach to reconstruct the phylogeny of Scleractinia (Cnidaria: Hexacorallia)

A well-supported evolutionary tree representing most major lineages of scleractinian corals is in sight with the development and application of phylogenomic approaches. Specifically, hybrid-capture techniques are shedding light on the evolution and systematics of corals. Here, we reconstructed a broad phylogeny of Scleractinia to test previous phylogenetic hypotheses inferred from a few molecular markers, in particular, the relationships among major scleractinian families and genera, and to identify clades that require further research. We analysed 449 nuclear loci from 422 corals, comprising 266 species spanning 26 families, combining data across whole genomes, transcriptomes, hybrid capture and low-coverage sequencing to reconstruct the largest phylogenomic tree of scleractinians to date. Due to the large number of loci and data completeness (less than 38% missing data), node supports were high across shallow and deep nodes with incongruences observed in only a few shallow nodes. The “Robust” and “Complex” clades were recovered unequivocally, and our analyses confirmed that Micrabaciidae Vaughan, 1905 is sister to the “Robust” clade, transforming our understanding of the “Basal” clade. Several families remain polyphyletic in our phylogeny, including Deltocyathiidae Kitahara, Cairns, Stolarski & Miller, 2012, Caryophylliidae Dana, 1846, and Coscinaraeidae Benzoni, Arrigoni, Stefani & Stolarski, 2012, and we hereby formally proposed the family name Pachyseridae Benzoni & Hoeksema to accommodate Pachyseris Milne Edwards & Haime, 1849, which is phylogenetically distinct from Agariciidae Gray, 1847. Results also revealed species misidentifications and inconsistencies within morphologically complex clades, such as Acropora Oken, 1815 and Platygyra Ehrenberg, 1834, underscoring the need for reference skeletal material and topotypes, as well as the importance of detailed taxonomic work. The approach and findings here provide much promise for further stabilising the topology of the scleractinian tree of life and advancing our understanding of coral evolution.

Microsatellite markers for Monitipora digitata designed using restriction-site associated DNA sequencing

Montipora digitata is a species belonging to the Acroporidae. In the Indo-Pacific region, M. digitata is widely distributed and is the dominant species of scleractinian coral in the South China Sea, however, there are currently no molecular markers suitable for assessing the species genetic diversity. Here, restriction-site associated DNA sequencing (RAD-seq) was used to isolate and characterize polymorphic microsatellite loci. A total of 317,361 RAD-tags were obtained using RAD-seq, including 6,778 microsatellite loci. Primer pairs for 106 loci were ordered and twenty-one polymorphic loci, that amplified reliably were identified. The number of alleles per locus were 2-7, observed heterozygosity was 0.111-0.556 with an average value of 0.285, and expected heterozygosity was 0.105- 0.802, with an average value of 0.536. Before Bonferroni correction 13 loci deviated significantly from the expectations of Hardy-Weinberg equilibrium (P < 0.05), after correction, two microsatellite loci deviated significantly (P < 0.0002). The polymorphic information content (PIC) ranged from 0.100-0.778, with 12 loci highly polymorphic (PIC > 0.5), six moderately polymorphic (0.25 < PIC < 0.5), and three loci with low polymorphism (PIC < 0.25). The microsatellite loci developed here will be effective tools for conservation genetic research on M. digitata.

Energy allocation trade-offs as a function of age in fungiid corals

To compete effectively, living organisms must adjust the allocation of available energy resources for growth, survival, maintenance, and reproduction throughout their life histories. Energy demands and allocations change throughout the life history of an organism, and understanding their energy allocation strategies requires determination of the relative age of individuals. As most scleractinian corals are colonial, the relationship between age and mass/size is complicated by colony fragmentation, partial mortality, and asexual reproduction. To overcome these limitations, solitary mushroom corals, Herpolitha limax from Okinawa, Japan and Fungia fungites from Okinawa and the Great Barrier Reef (GBR), Australia, were used to investigate how energy allocation between these fundamental processes varies as a function of age. Measurements of the relative growth, biochemical profiles, fecundity of individuals of different sizes, and the settlement success of their progeny have revealed physiological trade-offs between growth and reproduction, with increasing body mass ultimately leading to senescence. The importance of energy allocation for reproduction led us to examine the reproductive strategies and sex allocation in the two studied species. In the present study, the smallest individuals of both species studied were found to invest most of their energy in relative growth, showing higher lipid and carbohydrate content than the later stages. In medium-sized corals, this pattern was overturned in favour of reproduction, manifesting in terms of both the highest fecundity and settlement success of the resulting brooded larvae. Finally, a phase of apparent senescence was observed in the largest individuals, characterized by a decrease in most of the parameters measured. In addition, complex reproductive plasticity has been revealed in F. fungites in the GBR, with individual females releasing eggs, embryos, planulae, or a combination of these. These data provide the most direct estimates currently available for physiological, age-related trade-offs during the life history of a coral. The unusual reproductive characteristics of the GBR F. fungites indicate previously unknown layers of complexity in the reproductive biology of corals and have implications for their adaptive potential across a wide geographical scale.

A draft genome assembly of reef-building octocoral Heliopora coerulea

Coral reefs are under existential threat from climate change and anthropogenic impacts. Genomic studies have enhanced our knowledge of resilience and responses of some coral species to environmental stress, but reference genomes are lacking for many coral species. The blue coral Heliopora is the only reef-building octocoral genus and exhibits optimal growth at a temperature close to the bleaching threshold of scleractinian corals. Local and high-latitude expansions of Heliopora coerulea were reported in the last decade, but little is known about the molecular mechanisms underlying its thermal resistance. We generated a draft genome of H. coerulea with an assembled size of 429.9 Mb, scaffold N50 of 1.42 Mb and BUSCO completeness of 94.9%. The genome contains 239.1 Mb repetitive sequences, 27,108 protein coding genes, 6,225 lncRNAs, and 79 miRNAs. This reference genome provides a valuable resource for in-depth studies on the adaptive mechanisms of corals under climate change and the evolution of skeleton in cnidarian.

Structure of reef-building corals in tidal pools of a Marine Protected Area on the coastal zone of Royal Charlotte Bank, Eastern Brazil

ABSTRACT Brazilian coral reefs are the largest and richest reefs in the Southwestern Atlantic Ocean. Despite their historical and tourist importance, coral reefs on the east coast of Brazil remained unknown until recently. This study evaluated the structure of the reef-building coral community in three tidal pools along a gradient of anthropogenic disturbance. The pool known as Dolphin Pool is the warmest and has a high abundance of stony coral Siderastrea spp. One endemic species is on the national list of threatened species. Despite the high frequency of water temperatures above the alert threshold for mass bleaching events, the tidal pools have high densities of adults and recruits of reef-building corals. The results highlight the importance of reef formations on the coastal zone of the Royal Charlotte Bank, given the uniqueness of this area, and reinforce the need for further research and adoption of adaptive conservation approaches.

Role of the bicarbonate transporter SLC4γ in stony-coral skeleton formation and evolution.

Coral reefs are highly diverse ecosystems of immense ecological, economic, and aesthetic importance built on the calcium-carbonate-based skeletons of stony corals. The formation of these skeletons is threatened by increasing ocean temperatures and acidification, and a deeper understanding of the molecular mechanisms involved may assist efforts to mitigate the effects of such anthropogenic stressors. In this study, we focused on the role of the predicted bicarbonate transporter SLC4γ, which was suggested in previous studies to be a product of gene duplication and to have a role in coral-skeleton formation. Our comparative-genomics study using 30 coral species and 15 outgroups indicates that SLC4γ is present throughout the stony corals, but not in their non-skeleton-forming relatives, and apparently arose by gene duplication at the onset of stony-coral evolution. Our expression studies show that SLC4γ, but not the closely related and apparently ancestral SLC4β, is highly upregulated during coral development coincident with the onset of skeleton deposition. Moreover, we show that juvenile coral polyps carrying CRISPR/Cas9-induced mutations in SLC4γ are defective in skeleton formation, with the severity of the defect in individual animals correlated with their frequencies of SLC4γ mutations. Taken together, the results suggest that the evolution of the stony corals involved the neofunctionalization of the newly arisen SLC4γ for a unique role in the provision of concentrated bicarbonate for calcium-carbonate deposition. The results also demonstrate the feasibility of reverse-genetic studies of ecologically important traits in adult corals.

The 2022 summer marine heatwaves and coral bleaching in China's Greater Bay Area

From July to August 2022, scleractinian coral communities in China's Greater Bay Area (GBA) in the northern South China Sea (nSCS) experienced an unprecedented bleaching event, despite the fact that coral communities in this area are often considered coral thermal refugia due to their high latitude distribution. Field surveys of six sites covering three main coral distribution areas of the GBA revealed that coral bleaching occurred at all sites. Bleaching was more severe in shallow water (1–3 m) than in deep water (4–6 m), as indicated by both percent bleached cover (51.80 ± 10.04% vs. 7.09 ± 7.37%) and bleached colonies (45.86 ± 11.22% vs. 6.58 ± 6.53%). Coral genera Acropora, Favites, Montipora, Platygyra, Pocillopora, and Porites showed high susceptibility to bleaching, and Acropora and Pocillopora suffered high post-bleaching mortality. In the three areas surveyed, analysis of oceanographic data detected marine heatwaves (MHWs) during the summer, with mean intensities between 1.62 and 1.97 °C and durations between 5 and 22 days. These MHWs were primarily driven by increased shortwave radiation due to strong western Pacific Subtropical High (WPSH), combined with reduced mixing between the surface and deep upwelling waters due to reduced wind speed. Comparing with histological oceanographic data showed that the 2022 MHWs were unprecedented, and there was a significant increase in the frequency, intensity, and total days of MHWs during 1982–2022. Furthermore, the heterogeneous distribution of summer MHW characteristics indicates that the coastal upwelling may modulate the spatial distribution of summer MHWs in nSCS through its cooling effect. Overall, our study indicates that MHWs may have affected the structure of the subtropical coral communities in the nSCS, and impaired their potential as thermal refugia.

Species Diversity and Abundance of Corals and Fishes in A Marine Protected Area

This quantitative-descriptive study’s purpose was to gather information about the current state of fish and coral distribution in the Barangay Tamisan Marine Protected Area. Specifically, it aimed to determine the level of physicochemical parameters, reef health status, coral composition and abundance, reef fish abundance, and biomass in the study site. The study used line transect and fish visual methods. Results of the study revealed that the physicochemical parameters in the said area fall within the normal range which is favorable for the survival of fishes and corals in the study site. The Tamisan Marine Protected Area’s average cover of hard coral is 38.5% which falls under the category of “fair”. Corals with the greatest abundance are from the massive porites genera which compromises 70% of the hard coral cover. Nineteen species from different families of fishes in the study area and 1 class was identified, Actinopterygii. Among the species, it is Pomacentridae that has the greatest number of counts, that is 34. Other species identified were the Labridae, Siganidae, Ephinephilenae, Acanthurida, Balistidae. Apogonida, Scarida, Chaetodontidae, Caesionidae. Monacantidae, Tetraodontidae, Fistularidae, Synodontidae, Synanciinae and, Pomacantidae. The fishes in the study area have a diversity index of 0,820, representing a high index of diversity, but have very low fish biomass. The results implied that although the coral cover is fair and fishes are diverse, it still needs further studies on human activities to find the reason behind very low fish biomass. Keywords: fishes, reef health status, quantitative-descriptive study, Marine Protected Area, Mati City

Pervasive tandem duplications and convergent evolution shape coral genomes

BackgroundOver the last decade, several coral genomes have been sequenced allowing a better understanding of these symbiotic organisms threatened by climate change. Scleractinian corals are reef builders and are central to coral reef ecosystems, providing habitat to a great diversity of species.ResultsIn the frame of the Tara Pacific expedition, we assemble two coral genomes, Porites lobata and Pocillopora cf. effusa, with vastly improved contiguity that allows us to study the functional organization of these genomes. We annotate their gene catalog and report a relatively higher gene number than that found in other public coral genome sequences, 43,000 and 32,000 genes, respectively. This finding is explained by a high number of tandemly duplicated genes, accounting for almost a third of the predicted genes. We show that these duplicated genes originate from multiple and distinct duplication events throughout the coral lineage. They contribute to the amplification of gene families, mostly related to the immune system and disease resistance, which we suggest to be functionally linked to coral host resilience.ConclusionsAt large, we show the importance of duplicated genes to inform the biology of reef-building corals and provide novel avenues to understand and screen for differences in stress resilience.

Analisis Kesehatan Terumbu Karang Berdasarkan Kelimpahan Ikan Herbivora Di Perairan Labuan Bajo

Coral reef ecosystem is one of the ecosystems located in coastal areas which has a very important role for the community, both economically and ecologically. Rock or scleractinian corals are the main building blocks of coral reef ecosystems. The connectivity of coral reef ecosystems with other ecosystems has a very large influence on the life cycle of reef fish such as spawning, rearing, foraging, and sheltering places. Herbivorous fish are that eat turf algae or macroalgae that inhibit the recruitment of new corals. Labuan Bajo is one of the tourism destinations in Indonesia, especially marine tourism. Coral reefs in Labuan Bajo cover 10.8% of the total area of coral reefs in Indonesia located in Nusa Tenggara. The purpose of this study was to determine the health of coral reefs in the waters of Labuan Bajo. This research will be carried out from September to October 2021. The coral reef data collection method used is the Underwater Photo Transect (UPT), and for reef fish is using the Underwater Visual Census (UVC) method. Based on the research results, the percentage of hard coral is 20.16% of the total stations and rubble is 32.24%. The abundance of fish in Labuan Bajo waters ranges from 1608.89 - 4600.00 ind/ha, where the average abundance is 2919.78 ind/ha. All stations got a health index value of 3, this is indicated by the low coral cover, high coral resilience, and low herbivorous fish biomass obtained.

Heavy metal accumulation in the skeletons of scleractinian corals around the Gulf of Mannar Marine National Park, India

Heavy metal accumulation in the skeletons of scleractinian corals around the Gulf of Mannar Marine National Park, India

Endogenous viral elements reveal associations between a non-retroviral RNA virus and symbiotic dinoflagellate genomes

Endogenous viral elements (EVEs) offer insight into the evolutionary histories and hosts of contemporary viruses. This study leveraged DNA metagenomics and genomics to detect and infer the host of a non-retroviral dinoflagellate-infecting +ssRNA virus (dinoRNAV) common in coral reefs. As part of the Tara Pacific Expedition, this study surveyed 269 newly sequenced cnidarians and their resident symbiotic dinoflagellates (Symbiodiniaceae), associated metabarcodes, and publicly available metagenomes, revealing 178 dinoRNAV EVEs, predominantly among hydrocoral-dinoflagellate metagenomes. Putative associations between Symbiodiniaceae and dinoRNAV EVEs were corroborated by the characterization of dinoRNAV-like sequences in 17 of 18 scaffold-scale and one chromosome-scale dinoflagellate genome assembly, flanked by characteristically cellular sequences and in proximity to retroelements, suggesting potential mechanisms of integration. EVEs were not detected in dinoflagellate-free (aposymbiotic) cnidarian genome assemblies, including stony corals, hydrocorals, jellyfish, or seawater. The pervasive nature of dinoRNAV EVEs within dinoflagellate genomes (especially Symbiodinium), as well as their inconsistent within-genome distribution and fragmented nature, suggest ancestral or recurrent integration of this virus with variable conservation. Broadly, these findings illustrate how +ssRNA viruses may obscure their genomes as members of nested symbioses, with implications for host evolution, exaptation, and immunity in the context of reef health and disease.

Persentase Tutupan Karang Di Perairan Teluk Akle Kecamatan Semau Selatan Kabupaten Kupang Nusa Tenggara Timur

Akle Bay is one of marine aquaculture area in Semau island and it has coral reef potention. The coverage percentage of coral reef in the ocean might be decline by human activities and also by nature itself. The aimed of this research was analyzed to know the percentage of coral reef coverage in Akle Bay, South Semau District. This study conducted in Akle Bay, South Semau District on May 18, 2023st . Underwater Photo Transect (UPT) was used to take a sample in five meter depth at two different sites in Akle Bay waters. Data was analyzed by software CPCe 4.1. Result showed the highest benthic coverage percentage is soft coral. There were eleven genus of hard coral was found and its dominated by Porites genera. The percentage of hard coral coverage in S1 was 9.14%, while in S2 was 6.11% and was categorized in worst condition. The decline of coral reef coverage percentage in this area was expeted due to of human activities such as coral removal, the usage of anchor and the destructive fishing gear like a bomb, and also a sedimentation. According to the lifeform, covarage percentage of hard coral was dominated by coral branching. The average of current velocity in Akle Bay was 0,417 m/s with the range of waves was 0.1 to 0.5 meters. Conclusion of this research is the percentage of coral coverage in Akle Bay is worst. It was becacuse of human activities and sedimentation.

Different times, similar mechanism? Convergent patterns in light-induced phenotypic plasticity in Devonian and modern corals

Modern scleractinian corals can display high phenotypic plasticity, which reflects an interplay among various environmental controls, such as sediment input, water hydrodynamics or light intensity. In particular, the latter can strongly influence the morphology of coral species living across broad depth gradients. Light intensity was also a factor shaping the colonies of extinct Palaeozoic tabulate corals (Anthozoa: Tabulata). Based on gradual transitions in morphology observed in corals from the Middle Devonian (Givetian stage, ~ 385 Ma) mesophotic coral ecosystems (MCE) of the Aferdou el Mrakib reef (Anti-Atlas mountains, Morocco) and comparative material originating from different palaeobathymetric and biogeographical settings, we show that Devonian tabulate corals, such as Roseoporella and Alveolites, were characterised by high phenotypic plasticity and the ability to dramatically change their morphology depending on the inferred light conditions. Such a mechanism is similar to that observed in modern scleractinians, e.g. Porites sillimaniana. This recurring morphological theme suggests that Palaeozoic tabulate corals shared many functional characteristics of modern scleractinians.

A Red Sea Depth Record of the Coral-Dwelling Crab Opecarcinus (Decapoda: Cryptochiridae) in the Mesophotic Zone

Coral-dwelling gall crabs (Cryptochiridae) are obligate symbionts of stony corals and occur on shallow and deep reefs across the tropical belt. The circumtropical genus Opecarcinus associates with Agariciidae corals, a dominant component of Mesophotic Coral Ecosystems (MCEs). Here, we report the first Red Sea mesophotic record, with 89 m as the deepest record to date, for Opecarcinus—collected from Leptoseris cf mycetoseroides—from the NEOM marine area in Saudi Arabia. This observation reconfirms the depth range flexibility of Opecarcinus species and highlights the need for further mesophotic explorations of reef-associated fauna.

Applying Transfer Learning ResNet-50 for Tracking and Classification of A Coral Reef in Development The Mobile Application with Scrum Framework

A Coral Reef has an important role in keeping a balanced ecosystem in the ocean. This research aims to develop a mobile application to track and classify to identify Coral Reefs with a presentation of information names of species, the type of classification of coral (hard or soft coral), accuracy, and area distribution that has been recorded before in certain areas. This research, utilized Flutter for deploying a mobile application, Deep Learning of Transfer Learning (TL) ResNet-50 for the classification of Coral Reefs, and the Google Cloud Platform used to deploy Rest API and deploy model TL ResNet-50 has been created, then the MongoDB database for storing data of the Coral Reef. A species of Coral Reef that could be classified to identify i.e. Acropora Clathrata, Acropora Florida, Cyphastrea Microphthalma, Diploastrea Heliopora, and Pachyseris Speciosa. A total dataset of a Coral Reef has 2197 images and is trained with TL ResNet-50 and it has resulted in an accuracy of 0.9594 or 96% for the classification of Corel Reef. We used the Scrum framework to produce a product in a short time and assist to manage process application development.

Stony coral tissue loss disease induces transcriptional signatures of in situ degradation of dysfunctional Symbiodiniaceae

Stony coral tissue loss disease (SCTLD), one of the most pervasive and virulent coral diseases on record, affects over 22 species of reef-building coral and is decimating reefs throughout the Caribbean. To understand how different coral species and their algal symbionts (family Symbiodiniaceae) respond to this disease, we examine the gene expression profiles of colonies of five species of coral from a SCTLD transmission experiment. The included species vary in their purported susceptibilities to SCTLD, and we use this to inform gene expression analyses of both the coral animal and their Symbiodiniaceae. We identify orthologous coral genes exhibiting lineage-specific differences in expression that correlate to disease susceptibility, as well as genes that are differentially expressed in all coral species in response to SCTLD infection. We find that SCTLD infection induces increased expression of rab7, an established marker of in situ degradation of dysfunctional Symbiodiniaceae, in all coral species accompanied by genus-level shifts in Symbiodiniaceae photosystem and metabolism gene expression. Overall, our results indicate that SCTLD infection induces symbiophagy across coral species and that the severity of disease is influenced by Symbiodiniaceae identity.

Caribbean scleractinian corals exhibit highly variable tolerances to acute hypoxia

IntroductionClimate change, and the increase in sea surface temperature, is exacerbating ocean deoxygenation because of the inherent property of seawater to sequester less dissolved gas, such as oxygen, at warmer temperatures. While most coral reef studies focus on the effects of thermal stress and ocean acidification, few studies acknowledge the threat of hypoxia. Hypoxia is traditionally defined as 6.3 kPa (2 mg L-1 O2), however, a universal hypoxia threshold is not useful given the vast range of responses among marine organisms. The range of metabolic responses and tolerances to hypoxia are unknown for Caribbean coral species and their algal symbionts.ObjectiveHere, we quantified the spectrum of acute hypoxia tolerances and the range of metabolic responses of six ecologically and structurally important Caribbean coral species (Acropora cervicornis, Siderastrea radians, Siderastrea siderea, Porites astreoides, Porites porites, and Orbicella faveolata) and their algal symbionts (Symbiodinium, Breviolum, and Durusdinium spp.).MethodsA total of 24 coral fragments (4 individuals per species) were exposed to 10 distinct oxygen concentrations ranging from normoxia (20.38 kPa) to severe hypoxia (3.3 kPa). We used intermittent flow respirometry to measure coral host respiration in the dark and algal symbiont photosynthesis in the light at each oxygen level. We determined a line of best fit for the metabolic rate vs. PO2 data and calculated the critical oxygen partial pressure (PO2 crit), a method that has not been tested on symbiotic species.ResultsCoral species and their algal symbionts measured here displayed a wide range of hypoxia tolerances. For the coral hosts, PO2 crit values differed roughly two-fold ranging from 5.74 kPa to 16.93 kPa, and for the algal symbionts, PO2 crit values differed roughly three-fold ranging from 3.9 kPa to 11.3 kPa.DiscussionThese results should be regarded as a first step to characterizing the metabolic response and acute tolerance of multiple coral hosts and algal symbionts to a wide range of oxygen concentrations. Given that some PO2 crit values were above the generally accepted hypoxia threshold, these results have implications for the community composition of reefs under a rapidly changing climate and can guide purposeful reef restoration.