Scleractinian Corals Research Articles

Influence of reef habitat on coral microbial associations

AbstractCorals have complex symbiotic associations that can be influenced by the environment. We compare symbiotic dinoflagellate (family: Symbiodiniaceae) associations and the microbiome of five scleractinian coral species from three different reef habitats in Palau, Micronesia. Although pH and temperature corresponded with specific host‐Symbiodiniaceae associations common to the nearshore and offshore habitats, bacterial community dissimilarity analyses indicated minimal influence of these factors on microbial community membership for the corals Coelastrea aspera, Psammocora digitata, and Pachyseris rugosa. However, coral colonies sampled close to human development exhibited greater differences in microbial community diversity compared to the nearshore habitat for the coral species Coelastrea aspera, Montipora foliosa, and Pocillopora acuta, and the offshore habitat for Coelastrea aspera, while also showing less consistency in Symbiodiniaceae associations. These findings indicate the influence that habitat location has on the bacterial and Symbiodiniaceae communities comprising the coral holobiont and provide important considerations for the conservation of coral reef communities, especially for island nations with increasing human populations and development.

The effects of disease lesions and amoxicillin treatment on the physiology of SCTLD-affected corals

Metrics of coral physiology can be used to identify changes in coral health due to environmental stressors or management actions. One of the most unprecedented stressors to Caribbean corals is the spread of stony coral tissue loss disease (SCTLD), which also resulted in the novel management action of in-water amoxicillin treatments on active disease lesions. Though highly effective at halting lesions and preventing coral mortality, possible unintended consequences of topical application of amoxicillin to coral tissue were unknown. We used in-water instrumentation to measure and compare photosynthesis (P), respiration (R), P/R ratios, and calcification of corals that were visually healthy, actively diseased, and diseased but treated with amoxicillin paste. Measurements occurred across three time points and two species – Orbicella faveolata and Montastraea cavernosa. Across all metrics, treatment type did not cause significant differences, indicating that neither SCTLD lesions nor amoxicillin treatments impacted the physiology of adjacent tissues. There were significant variations among time points, which may have resulted from changes to coral health across the reef, variations due to environmental variables, or other unknown factors. We suggest that physiological metrics could be an interesting way to fate track coral health across short- and long-term timeframes. We also conclude that amoxicillin treatments as a tool to halt SCTLD are not detrimental to respiration, photosynthesis, or calcification rates of adult corals.

Leveraging the Red List of Ecosystems for action on coral reefs through the Kunming‐Montreal Global Biodiversity Framework

AbstractCountries have committed to conserving and restoring ecosystems after signing the Kunming‐Montreal Global Biodiversity Framework (GBF). The IUCN Red List of Ecosystems (RLE) will serve as a headline indicator to track countries' progress toward achieving this goal. Using Kenyan coral reefs, we demonstrate how nations implementing the GBF can use standardized estimates of ecosystem degradation from RLE assessments to support site‐specific management decisions. We undertook a reef‐by‐reef analysis to evaluate the relative decline of four key ecosystem components over the past 50 years: hard corals, macroalgae, parrotfish, and groupers. Using the two benthic indicators, we also calculated standardized estimates of state to identify reef sites which maintain a better condition through time relative to adjacent sites. Kenya's coral reefs have degraded across all four ecosystem components. At more than half the monitored sites parrotfish and grouper abundance declined by more than 50%, while coral cover and macroalgae‐coral ratio declined by at least 30%. This resulted in an Endangered threat status for coral reefs in Kenya (under criterion D of the RLE). The results can guide management actions related to 9 of the 23 GBF targets. For example, we identified several sites with relatively healthy benthic and fish communities as candidate areas for protection measures under Target 3. The RLE has a key role to play in monitoring and meeting the goals and targets of the GBF, and our work demonstrates how using the wealth of data within these assessments can inform local‐scale ecosystem management and amplify the GBF's impact.

Acclimation and size influence predation, growth, and survival of sexually produced Diploria labyrinthiformis used in restoration

Stony coral tissue loss disease (SCTLD) has swept through Florida reefs and caused mass mortality of numerous coral species. In the wake of these losses, efforts are underway to propagate coral species impacted by SCTLD and promote population recovery. However, numerous knowledge gaps must be addressed to effectively grow, outplant, and restore populations of the slower growing, massive species that were lost. Here, we used sexual recruits of Diploria labyrinthiformis spawned in captivity to understand how conditioning, coral size, and nutritional status at outplanting affect coral survivorship, growth, and susceptibility to predation. We found that ex situ conditioning with supplemental feeding increased coral growth rates, resulting in larger sized corals at the time of outplanting. In turn, these corals had higher growth rates in the field and a lower probability of being removed by predators than outplants that were conditioned in in situ nurseries. Additionally, we found that coral size was an important predictor of survivorship, suggesting that hastening the speed at which young corals grow and outplanting larger juveniles can improve restoration outcomes. Taken together, our results suggest that providing supplemental food to corals at ex situ facilities confers benefits that could help restore populations of massive coral species impacted by SCTLD.

Spatial Variation in Upper Limits of Coral Cover on the Great Barrier Reef

ABSTRACTAimIdentifying the maximum coral cover that a coral community can sustain (i.e., its ‘upper limit’) is important for predicting community dynamics and improving management strategies. Here, we quantify the relationship between estimated upper limits and key environmental factors on coral reefs: hard substrate availability, temperature and water clarity.LocationGreat Barrier Reef (GBR), Australia (over 1400 km).Time Period1990 to 2022.Major Taxa StudiedScleractinian corals.MethodsWe used 32 years of data on coral cover around reef perimeters. Each reef was divided into four wave‐exposure habitats depending on prevailing wind conditions. For each site, we determined if hard coral cover had reached a plateau or upper limit. Next, we extracted existing estimates of hard substrate availability, modelled water temperature and Secchi depth. Then, we quantified the relationship between these environmental variables and the upper limits.ResultsWe found varying upper limits across the GBR, with a median of 33% coral cover and only 17% of the estimated upper limits exceeded 50% coral cover. Upper limits increased towards the southern reefs. Our results show that upper limits increased with increasing hard substrate availability and decreased with temperature and, to a lesser extent, with water clarity.Main ConclusionsThe upper limits estimated in this study are much lower than what is commonly assumed when modelling ecological dynamics, most likely resulting in predicted recovery rates being inappropriately high. Although hard substrate ultimately restricted upper limits, there are mechanisms constraining the proportion of hard substrate that is covered by hard corals. The negative relationship between temperature and upper limits cannot be explained by changes in macroalgal abundance but may be related to changes in species composition. The quantitative relationships between the upper limits of coral cover and environmental variables will provide critical information to prioritise sites for management interventions.

Coral photosymbiosis on Mid-Devonian reefs.

The ability of stony corals to thrive in the oligotrophic (low-nutrient, low-productivity) surface waters of the tropical ocean is commonly attributed to their symbiotic relationship with photosynthetic dinoflagellates1,2. The evolutionary history of this symbiosis might clarify its organismal and environmental roles3, but its prevalence through time, and across taxa, morphologies and oceanic settings, is currently unclear4-6. Here we report measurements of the nitrogen isotope (15N/14N) ratio of coral-bound organic matter (CB-δ15N) in samples from Mid-Devonian reefs (Givetian, around 385 million years ago), which represent a constraint on the evolution of coral photosymbiosis. Colonial tabulate and fasciculate (dendroid) rugose corals have low CB-δ15N values (2.51 ± 0.97‰) in comparison with co-occurring solitary and (pseudo)colonial (cerioidor phaceloid) rugose corals (5.52 ± 1.63‰). The average of the isotopic difference per deposit (3.01 ± 0.58‰) is statistically indistinguishable from that observed between modern symbiont-barren and symbiont-bearing corals (3.38 ± 1.05‰). On the basis of this evidence, we infer that Mid-Devonian tabulate and some fasciculate (dendroid) rugose corals hosted active photosymbionts, while solitary and some (pseudo)colonial (cerioidor phaceloid) rugose corals did not. The low CB-δ15N values of the Devonian tabulate and fasciculate rugose corals relative to the modern range suggest that Mid-Devonian reefs formed in biogeochemical regimes analogous to the modern oligotrophic subtropical gyres. Widespread oligotrophy during the Devonian may have promoted coral photosymbiosis, the occurrence of which may explain why Devonian reefs were the most productive reef ecosystems of the Phanerozoic.

Patterns of fish assemblage structure on reefs with varying degrees of hard coral and soft coral dominance in Okinawa Island, Japan

Patterns of fish assemblage structure on reefs with varying degrees of hard coral and soft coral dominance in Okinawa Island, Japan

Gene expression microarray analysis during metamorphosis and early calcification in the scleractinian coral Acropora millepora

ABSTRACT In the face of global warming and ocean acidification, understanding the cellular mechanisms underlying coral metamorphosis and early calcification is essential, as both processes are likely to be affected by a changing environment. In this study, we used cDNA microarray expression analysis to compare transcription profiles between four distinct life stages in the ‘complexa’ coral Acropora millepora: 1) aposymbiotic non-calcifying planula, 2) aposymbiotic calcifying flat polyp, 3) aposymbiotic calcifying primary polyp and 4) symbiotic adult tip. Highly up-regulated genes in planulae were molecules involved in calcium signalling, lipid metabolism and development. Transcripts up-regulated in post-settlement juvenile stages regulate tissue morphogenesis, cell division and responses to oxidative stress. Transcripts with the highest expression in adult polyps are involved in responses to abiotic stimuli and asexual reproduction. Transcripts up-regulated in calcifying stages included carbonic anhydrases and organic matrix components. Additionally, our results suggest an overlap between intracellular secondary messengers following settlement and metamorphosis. A subset of fluorescent proteins were up-regulated at the planula stage but down-regulated after settlement, supporting the idea that these molecules might have a role in quenching reactive oxygen species. Altogether, our results suggest that Acropora developmental stages are transcriptionally distinct units in which transcription profiles reflect responses to different physiological and ecological conditions.

Differential spatio-temporal responses of Red Sea coral reef benthic communities to a mass bleaching event

Understanding how coral reefs respond to disturbances is fundamental to assessing their resistance and resilience, particularly in the context of climate change. Due to the escalating frequency and intensity of coral bleaching events, it is essential to evaluate spatio-temporal responses of coral reef communities to disentangle the mechanisms underlying ecological changes. Here, we used benthic data collected from 59 reefs in the Red Sea over five years (2014–2019), a period that encompasses the 2015/2016 mass bleaching event. Reefs were located within three different geographic regions with different environmental settings: north (Duba; Al Wajh), central (Jeddah; Thuwal), and south (Al Lith; Farasan Banks; Farasan Islands). Coral community responses were region-specific, with communities in the south being more promptly affected than those in the northern and central regions, with hard and soft coral cover dropping drastically in several reefs from around > 40% to < 5% two years after bleaching. Coral bleaching effects were particularly evident in the decrease of cover in branching corals. Overall, we documented a shift towards a dominance of macroalgae, turf algae, and crustose coralline algae (CCA). Using remote sensing data, we analyzed sea surface temperature (SST) regimes at the study sites to infer potential drivers of changes in benthic composition. Both SST and Degree Heating Weeks (DHW) only partially aligned with the responses of benthic communities, highlighting the need for more accurate predictors of coral bleaching in the Red Sea. In times of intense coastal development along Saudi Arabia’s Red Sea coast, our study provides crucial baseline information on developments in coral reef community composition, as well as to guide decision-making, namely restoration efforts.

Assessment of nutrient amendments on stony coral tissue loss disease in Southeast Florida

Assessment of nutrient amendments on stony coral tissue loss disease in Southeast Florida

Environmental and ecological factors associated with stinging jellyfish at a tourism hotspot in the Gulf of Thailand

The waters of Thailand are associated with some of the most severe cases of envenomation from jellyfish in Asia, often attributed to the extensive marine recreational tourism industry it supports. The western Gulf of Thailand in particular has been shown to host among the highest abundances of box jellyfish, while also being home to some of the highest marine recreational tourism, such as along the Koh Samui archipelago. Here we utilise aspects of the same tourism industry to develop a deeper understanding of stinging jellyfish population dynamics, by combining citizen science at the island of Koh Tao, with dedicated in-situ surveys and remote sensing data. Our analyses of 170 box jellyfish sightings and 81 blooms of Pelagia sp. across a six-year period revealed a strong seasonal trend, with both groups being most abundant between July and December. Decision tree analysis of the complete observation dataset and multiple environmental variables revealed a combination of precipitation and lunar cycle to be the strongest predictors of the assessed stinging jellyfish at Koh Tao. Furthermore, blooms of Pelagia sp. were associated with extensive medusivory by a large diversity of predators, including reef building corals. These observations add to the growing literature showing that scleractinian corals are readily able to ingest larger prey items, either by solitary or protocooperative feeding strategies. Meanwhile, no consumption of box jellyfish medusae was recorded during the study. These findings may allow for improved tourism management practices while also supporting a wider biogeographic assessment of stinging jellyfish in south-east Asia.

Replayed reef sounds induce settlement of Favia fragum coral larvae in aquaria and field environmentsa).

Acoustic cues of healthy reefs are known to support critical settlement behaviors for one reef-building coral, but acoustic responses have not been demonstrated in additional species. Settlement of Favia fragum larvae in response to replayed coral reef soundscapes were observed by exposing larvae in aquaria and reef settings to playback sound treatments for 24-72 h. Settlement increased under 24 h sound treatments in both experiments. The results add to growing knowledge that acoustically mediated settlement may be widespread among stony corals with species-specific attributes, suggesting sound could be one tool employed to rehabilitate and build resilience within imperiled reef communities.

Biodiversity and antifouling activity of microbes associated with gorgonian corals Leptogorgia rigida and Menella kanisa from the South China Sea

Recently, coral-associated microorganisms have attracted widespread attention, and most of these studies have focused on stony and soft corals. However, our knowledge of the diversity and bioactivity of microorganisms in gorgonian corals is still limited. In this study, the biodiversity of microbes in two gorgonian corals (Leptogorgia rigida and Menella kanisa) from the South China Sea was investigated by combining traditional culture method with molecular biology technique (bacterial 16S or fungal internal transcribed spacer (ITS) rRNA gene sequences). A total of 216 bacterial and 98 fungal isolates were obtained using 4 different isolation media. These isolates were identified and belonged to 31 bacterial and 12 fungal species, suggesting an unexpectedly diverse microbial community harbored in the South China Sea gorgonian corals L. rigida and M. kanisa. Furthermore, 56% of the tested microbial isolates displayed various antifouling activities against four biofouling organisms (including two microfouling bacteria Micrococcus luteus and Shewanella onedensis, and two macrofouling organisms Bugula neritina and Balanus amphitrite). Among the microbial isolates with antifouling activity, Bacillus firmus SCAU-038 and Streptomyces parvulus SCAU-062 displayed moderate or strong antifouling activity against all tested biofouling organisms. This is the first study on the biodiversity and antifouling activity of microorganisms associated with gorgonians L. rigida and M. kanisa from the South China Sea. These results contribute to the further understanding of microorganisms associated with gorgonian corals and provide potential resources for new natural antifouling agents.

Sunscreens: potential hazards to environmental and human health

The increasing demand for natural products in the United States reflects a cultural shift towards health and sustainability. This trend infiltrates consumer sectors such as the sunscreen industry, amidst concerns about health and environmental impacts of chemical ingredients. The Hawaii Sunscreen Ban has intensified sunscreen formula safety discussions, particularly regarding butylparaben, oxybenzone, and octinoxate. Even at low concentrations, these compounds bleach hard corals eventually leading to their death. As well, these chemicals pose threats to marine ecosystems and raise concerns about human health, particularly systemic absorption and the possibility of causing endocrine disruption. While some argue for chemical-based sunscreens for skin cancer prevention, others advocate for mineral-based alternatives that avoid harmful ingredients. However, public opinion on sunscreen varies, influenced by adverse reactions, socioeconomic status, gender, and cultural perceptions. Future studies should explore diverse demographic perspectives and long-term health and environmental impacts of products containing potentially toxic ingredients. As well, effective communication strategies to promote sunscreen safety and encourage sustainable sun protection practices is needed.

Untargeted Metabolomics Approach for the Discovery of Salinity-Related Alkaloids in a Stony Coral-Derived Fungus Aspergillus terreus

As a part of the important species that form coral reef ecosystems, stony corals have become a potential source of pharmacologically active lead compounds for an increasing number of compounds with novel chemical structures and strong biological activity. In this study, the secondary metabolites and biological activities are reported for Aspergillus terreus C21-1, an epiphytic fungus acquired from Porites pukoensis collected from Xuwen Coral Reef Nature Reserve, China. This strain was cultured in potato dextrose broth (PDB) media and rice media with different salinities based on the OSMAC strategy. The mycelial morphology and high-performance thin layer chromatographic (HPTLC) fingerprints of the fermentation extracts together with bioautography were recorded. Furthermore, an untargeted metabolomics study was performed using principal component analysis (PCA), orthogonal projection to latent structure discriminant analysis (O-PLSDA), and feature-based molecular networking (FBMN) to analyze their secondary metabolite variations. The comprehensive results revealed that the metabolite expression in A. terreus C21-1 differed significantly between liquid and solid media. The metabolites produced in liquid medium were more diverse but less numerous compared to those in solid medium. Meanwhile, the mycelial morphology underwent significant changes with increasing salinity under PDB cultivation conditions, especially in PDB with 10% salinity. Untargeted metabolomics revealed significant differences between PDB with 10% salinity and other media, as well as between liquid and solid media. FBMN analysis indicated that alkaloids, which might be produced under high salt stress, contributed largely to the differences. The biological activities results showed that six groups of crude extracts exhibited acetylcholinesterase (AChE) inhibitory activities, along with 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging and antibacterial activities. The results of this study showed that the increase in salinity favored the production of unique alkaloid compounds by A. terreus C21-1.

Endolithic Algae (Ostreobium) Diversity in Porites Corals at the Western Atlantic and Tropical Eastern Pacific

ABSTRACTOstreobium comprises endolithic algae commonly seen in conjunction with scleractinian corals. In the past, it was solely recognized as a coral skeleton bioeroder. Their relationship with corals is critical because they give photosynthetic byproducts and help the coral when it loses its primary symbionts due to stress. The variety of these algae in coral species of the genus Porites in the Tropical Eastern Pacific and western Atlantic was investigated. Ostreobium samples from seven Porites species including two from the Tropical Eastern Pacific (TEP) (P. panamensis and P. lobata) and five from the Caribbean (P. furcata, P. porites, P. colonensis, P. branneri, and P. astreoides) were extracted. Published rbcL sequences from algae found within various coral species from other parts of the world were also compared. A biogeographic analysis and two methodologies, PTP (Poisson tree process) and GMYC (general mixed Yule‐coalescent), were used to delineate the different species. The findings revealed a significant degree of genetic diversity within Ostreobium, with more than 15 groups of not more than three individuals and 40 individual lineages. Its origins date back to the Ordovician, 500 Ma, and it does not appear to preserve host specificity. The sampled locations still have a wide variety of Ostreobium. Biogeographically patterns were also confirmed, making it impossible to pinpoint the precise origins of most clades. The ancestry analyses revealed convergent events for not only the emergence of Ostreobium in a few genera of local corals, but also the phenomenon occurred in genera from far‐off places.

Bayesian clustering of spatially distributed compositional data with application to the Great Barrier Reef.

The relative abundance of groups of species is often used in ecological surveys to estimate community composition, a metric that reflects patterns of commonness and rarity of biological assemblages. The focus of this paper is measurements of the abundances of four benthic groups (that live on the seafloor) at several reefs on Australia's Great Barrier Reef (GBR) gathered between 2012 and 2017. In this paper we develop a statistical model to find clusters of locations with similar composition. We examine the changes in clusters during a period impacted by an unprecedented sequence of extreme environmental disturbances. To achieve this, we propose a model that incorporates the geographical location of the data, accounting for the possibility that nearby reefs are similar in composition. This is accomplished with a Dirichlet mixture model and a Potts distribution on the cluster assignments. Non-availability of the normalised Potts distribution makes Bayesian inference a doubly-intractable task. To circumvent this additional inferential challenge, an approximate exchange algorithm is specified. The analysis of the 2012 data, collected before the weather disturbances, reveals four clusters. The four groups highlight the primary habitat patterns in the 2012 GBR, each with distinct ecological characteristics: (1) areas with above-average soft coral abundance, (2) sand-dominated regions commonly found in the central part, (3) southern reefs with a more balanced distribution of species, and (4) habitats dominated by algae and hard corals. Compared to subsequent surveys conducted after disturbances, there is evidence of a decline in the number of clusters and a simplification of reef composition at the regional scale.

Spatial structuring of coral traits along a subtropical-temperate transition zone persists despite localised signs of tropicalisation

AbstractClimate-driven species range expansions are underway with more tropically affiliated species, including Scleractinian corals, becoming increasingly abundant at higher latitudes. However, uncertainty remains on how these range shifts will affect reef-scale ecosystem processes, which will ultimately depend on the traits of the taxa that dominate these assemblages. Here, we quantified spatiotemporal patterns in the taxonomic and trait structure of coral assemblages along the subtropical-temperate coast of Western Australia (27°–34°S). Coral abundance was generally low and coral cover &lt; 5% across our study sites. Coral assemblages shared similarities in morphological trait structures across the latitudinal gradient, mostly characterised by taxa with simple morphologies; yet subtle differences were also observed across latitudes, with high-latitude corals characterised by slower growth rates and reduced maximum colony sizes. We found a 3.4-fold increase (from 1 to 3.4 individuals m−2) in coral abundance at one heavily disturbed location, where canopy-forming seaweeds were replaced by turfing algae, a pattern that was partly driven by an increase in the relative contribution of warm affinity taxa, such as Acropora spp. We predicted these changes would be reflected in different components of functional diversity; yet, despite a localised signal of tropicalisation, we only observed subtle changes in the functional identity, richness, evenness, and divergence. The spatially invariant trait structure of coral assemblages suggests that the nature of ecosystem functions will likely remain unchanged during early stages of tropicalisation, and hence their contribution to temperate reef-scale ecological processes will depend on dominance over other benthic foundational species.

Long-term dynamics of hard coral cover across Indonesia

Long-term dynamics of hard coral cover across Indonesia

Development and validation of an experimental life support system to study coral reef microbial communities

In the present study, we developed and validated an experimental life support system (ELSS) designed to investigate coral reef associated bacterial communities. The microcosms in the ELSS consisted of coral reef sediment, synthetic seawater, and specimens of five benthic reef species. These included two hard corals Montipora digitata and Montipora capricornis, a soft coral Sarcophyton glaucum, a zoanthid Zoanthus sp., and a sponge Chondrilla sp.. Physicochemical parameters and bacterial communities in the ELSS were similar to those observed at shallow coral reef sites. Sediment bacterial evenness and higher taxonomic composition were more similar to natural-type communities at days 29 and 34 than at day 8 after transfer to the microcosms, suggesting microbial stabilization after an initial recovery period. Biotopes were compositionally distinct but shared a number of ASVs. At day 34, sediment specific ASVs were found in hosts and visa versa. Transplantation significantly altered the bacterial community composition of M. digitata and Chondrilla sp., suggesting microbial adaptation to altered environmental conditions. Altogether, our results support the suitability of the ELSS developed in this study as a model system to investigate coral reef associated bacterial communities using multi-factorial experiments.