Coral Bleaching Research Articles

High diversity and abundance of fish and coral in an artificial breakwater in Colombo, Sri Lanka

The diversity of reef fishes and the diversity and abundance of corals in artificial breakwaters were studied between June and August 2023 in Port City, Colombo in the Western Province of Sri Lanka. Four methods were used: visual census using video, photographs, stationary point count and environmental DNA (eDNA). A total of 137 fish species, 74 coral species and 175 other species were recorded using the four methods. There were similarities and differences between the methods for recording fish, corals and other species. Only three fish species: Moon wrasse (Thalassoma lunare); Yellowtail fusilier (Caesio cuning) and Diamond fish (Monodactylus argenteus) were recorded by all methods. The highest number of fish species was recorded by video, followed by photographs, eDNA and stationary point count in the sequence. Coral cover ranged from 9 to 50.8% and mean live coral varied from 24.4% to 34.5 ± 5.2%. The dominant coral species was Pocillopora damicornis. Rare observations of coral bleaching (n=1) and frequent observations of marine debris (n=20) and coral damage (n=25) were recorded. Species detection using eDNA is a biomonitoring tool that did not add significantly to the list of fish and corals, but included many microscopic groups such as bacteria, diatoms and ciliates that were not recorded using other methods, and provided new ecological insights into marine systems. This is the first use of multiple monitoring tools to identify and compare methods for the biodiversity of marine fish, coral and other species in Sri Lankan marine waters.

Bleached Coral Supports High Diversity and Heterogeneity of Bacterial Communities: Following the Rule of the ‘Anna Karenina Principle’

Coral-associated bacteria are sensitive to the health status of coral and proven biomarker(s) of the coral bleaching. However, whether coral specificity or health status play a key role when coral-associated bacteria responding to coral bleaching is not known. Therefore, the bacterial communities of five species of healthy and bleached corals, Acropora millepora, Favites abdita, Galaxea fascicularis, Dipsastraea speciosa and Pocillopora damicornis, were collected along the coast of Sanya, South China Sea and targeted for associated bacterial studies. The relative abundance of the dominant class Gammaproteobacteria tended to be higher in healthy corals, while Alphaproteobacteria were more abundant in bleached corals. Dominant genus Achromobacter demonstrated higher relative abundance in healthy corals (0.675) than in bleached corals (0.151). Most of the bleached corals had high α diversity, β dispersion, heterogeneity and complexity of the co-occurrence network of bacterial communities, which support the ‘Anna Karenina Principle (AKP)’ of diverse in threatened objects and conserved in healthy ones. The bacterial communities in the bleached corals were mostly involved in the selection process, and communities in the healthy corals were involved in the undominated process, which is obtained based on the null model test of β nearest-taxon-index (βNTI) and Bray–Curtis-based Raup–Crick (RCBray). This evidence further confirmed the AKP and revealed that the bacterial communities in the bleached corals were driven by deterministic factors. These findings provide valuable insights into the connection between bacterial and coral status, and the application of the AKP in the changing patterns of bacterial communities during coral bleaching.

Changing disturbance regimes, material legacies, and stabilizing feedbacks: Dead coral skeletons impair key recovery processes following coral bleaching.

Ecosystem responses to disturbance depend on the nature of the perturbation and the ecological legacies left behind, making it critical to understand how climate-driven changes in disturbance regimes modify resilience properties of ecosystems. For coral reefs, recent increases in severe marine heat waves now co-occur with powerful storms, the historic agent of disturbance. While storms kill coral and remove their skeletons, heat waves bleach and kill corals but leave their skeletons intact. Here, we explored how the material legacy of dead coral skeletons modifies two key ecological processes that underpin coral reef resilience: the ability of herbivores to control macroalgae (spatial competitors of corals), and the replenishment of new coral colonies. Our findings, grounded by a major bleaching event at our long-term study locale, revealed that the presence of structurally complex dead skeletons reduced grazing on turf algae by ~80%. For macroalgae, browsing was reduced by >40% on less preferred (unpalatable) taxa, but only by ~10% on more preferred taxa. This enabled unpalatable macroalgae to reach ~45% cover in 2 years. By contrast, herbivores prevented macroalgae from becoming established on adjacent reefs that lacked skeletons. Manipulation of unpalatable macroalgae revealed that the cover reached after 1 year (~20%) reduced recruitment of corals by 50%. The effect of skeletons on juvenile coral growth was contingent on the timing of settlement relative to the disturbance. If corals settled directly after bleaching (before macroalgae colonized), dead skeletons enhanced colony growth by 34%, but this benefit was lost if corals colonized dead skeletons a year after the disturbance once macroalgae had proliferated. These findings underscore how a material legacy from a changing disturbance regime can alter ecosystem resilience properties by disrupting key trophic and competitive interactions that shape post-disturbance community dynamics.

Deciphering mechanisms of UV filter (benzophenone-3)- and high temperature-induced adverse effects in the coral Acropora tenuis, using ecotoxicogenomics

Coral reefs are at risk of bleaching due to various environmental and anthropogenic stressors such as global warming and chemical pollutants. However, there is little understanding of stressor-specific mechanisms that cause coral bleaching. Therefore, conducting accurate ecotoxicological risk assessments and deciphering modes of action of potentially deleterious ultraviolet (UV) filters (sunscreen compounds) are crucial issues. In this study, we evaluated the toxicity and bleaching effect of benzophenone-3 (BP-3), which is widely used in sunscreen products, on the reef-building coral Acropora tenuis. Furthermore, to understand differences in UV filter- and temperature-induced adverse effects, a comparative ecotoxicogenomic approach using RNA-seq was integrated into a toxicity test to clarify differences in gene expression changes induced by BP-3 and heat stress (31 °C). The lethal concentration 50 % (LC50) was calculated as 3.9 mg/L, indicating that the aquatic environmental risk on corals posed by BP-3 was low based on the risk assessment in this study. Differentially expressed genes related to oxidative stress and extracellular matrix organization were involved in coral responses to both BP-3 and heat stress, but their patterns differed. Whereas immune and heat-shock responses were activated in response to heat stress, activation of a drug metabolism pathway and several signal transduction pathways were identified in BP-3 treatment groups. Our study enhances understanding of stress responses in corals induced by UV filters and thermal stress. Using potential gene markers identified in this study for eco-epidemiological surveys of stressed corals, we urgently need to develop effective countermeasures.

A generalized machine learning model for long-term coral reef monitoring in the Red Sea

Coral reefs, despite covering less than 0.2 % of the ocean floor, harbor approximately 35 % of all known marine species, making their conservation critical. However, coral bleaching, exacerbated by climate change and phenomena such as El Niño, poses a significant threat to these ecosystems. This study focuses on the Red Sea, proposing a generalized machine learning approach to detect and monitor changes in coral reef cover over an 18-year period (2000–2018). Using Landsat 7 and 8 data, a Support Vector Machine (SVM) classifier was trained on depth-invariant indices (DII) derived from the Gulf of Aqaba and validated against ground truth data from Umluj. The classifier was then applied to Al Wajh, demonstrating its robustness across different sites and times. Results indicated a significant decline in coral cover: 11.4 % in the Gulf of Aqaba, 3.4 % in Umluj, and 13.6 % in Al Wajh. This study highlights the importance of continuous monitoring using generalized classifiers to mitigate the impacts of environmental changes on coral reefs.

Pushing the limits: expanding the temperature tolerance of a coral photosymbiont through differing selection regimes.

Coral thermal bleaching resilience can be improved by enhancing photosymbiont thermal tolerance via experimental evolution. While successful for some strains, selection under stable temperatures was ineffective at increasing the thermal threshold of an already thermo-tolerant photosymbiont (Durusdinium trenchii). Corals from environments with fluctuating temperatures tend to have comparatively high heat tolerance. Therefore, we investigated whether exposure to temperature oscillations can raise the upper thermal limit of D. trenchii. We exposed a D. trenchii strain to stable and fluctuating temperature profiles, which varied in oscillation frequency. After 2.1 yr (54-73 generations), we characterised the adaptive responses under the various experimental evolution treatments by constructing thermal performance curves of growth from 21 to 31°C for the heat-evolved and wild-type lineages. Additionally, the accumulation of extracellular reactive oxygen species, photophysiology, photosynthesis and respiration rates were assessed under increasing temperatures. Of the fluctuating temperature profiles investigated, selection under the most frequent oscillations (diurnal) induced the greatest widening of D. trenchii's thermal niche. Continuous selection under elevated temperatures induced the only increase in thermal optimum and a degree of generalism. Our findings demonstrate how differing levels of thermal homogeneity during selection drive unique adaptive responses to heat in a coral photosymbiont.

Can Coral Reefs Be Saved?: Mass bleaching events threaten corals worldwide.

Can Coral Reefs Be Saved?: Mass bleaching events threaten corals worldwide.

Species-specific effects of light and temperature on photosynthesis and respiration among Symbiodiniaceae (Dinophyceae)

Coral reefs are exposed to various environmental stressors that cause bleaching events, whereby endosymbiotic microalgae (Symbiodiniaceae) disassociate from coral hosts. Bleached corals are compromised and face mortality. The combination of high-light exposure and elevated seawater temperature often lead to coral bleaching. The physiological properties of the Symbiodiniaceae within the coral tissues contribute to the thermal tolerance of the holobiont (the host and all its symbionts). The present study aimed to investigate the effects of light and temperature stress on four Symbiodiniaceae species from three genera with respect to photosynthetic oxygen production and consumption. Under control conditions, the species displayed predominantly low-to-moderate light requirements for photosynthesis with increased photoinhibition at higher photon flux rates. After 30 days of heat acclimation at 32 °C, maximum photosynthetic activity declined in Effrenium voratum, doubled in Fugacium kawagutii, and remained unchanged in Breviolum psygmophilum. In subsequent acute heating assays, species-specific effects on maximum photosynthetic activity were observed. Photosynthesis in all species declined across a temperature gradient between 25 and 39 °C in the acute heating assays; full inhibition occurred at 37 °C in B. psygmophilum and E. voratum and at 39 °C in B. aenigmaticum and F. kawagutii. In contrast, respiration remained largely constant in all species across temperatures. Our data point to species-specific photophysiological traits that lead to different thermal tolerances among Symbiodiniaceae.

Colors of the ocean: Changes in the Anthropocene

Changes in the color of the ocean reflect how changes in Earth’s climate are transforming plankton ecosystems. Collecting data on both surface and underwater coloration is essential to monitoring the health of marine ecosystems across the ocean. Variations in ocean surface color, measured by satellites, hold information about the composition of plankton ecosystems. These ecosystems are sensitive to ocean temperature and to the availability of nutrients and light in the ocean. In underwater habitats, monitoring coral bleaching events serves as an important means for evaluating the health of reef ecosystems. Yet certain challenges remain to be addressed for acquiring and processing data in a standardized and reliable fashion. Current and future policies can be centered around data acquisition and integration as well as efforts for universal collaboration and broader societal impacts.

Back-to-back bleaching events in Peninsular Malaysia (2019–2020) selectively affect hard coral taxa across- and within-reef scales

The impacts of (repeat) bleaching events and the differential heat stress susceptibility of hard coral taxa are largely unknown in Malaysia, although it is part of the greater coral triangle. Here we determined bleaching trajectories of 46 hard coral taxa across- and within-reef scales based on data recorded during the first reported back-to-back coral bleaching occurrences in Malaysia between May 2019 and September 2020. Although the severity of coral bleaching in both years did not correspond to the rather small magnitude of heat stress observed, i.e., Degree Heating Weeks (DHW) of 1.05 °C-weeks and 0 °C-weeks in 2019 and 2020 respectively, we observed high levels of bleaching (55.21% and 26.63% of all surveyed colonies in 2019 and 2020, respectively). Notably, the bleaching response for both consecutive years was highly taxon-specific and significantly varied across- and within-reef scales. Mortality rates overall were low following the 2019 event, likely due to a rapid decrease in heat stress. Five of the 46 surveyed hard coral taxa exhibited more severe bleaching in 2020, despite a lower heat stress load. Interestingly, we observed low bleaching of ascribed susceptible taxa such as Acropora and Montipora, while we found taxa considered to be resilient, e.g. Heliopora and Porites, to exhibit severe bleaching, suggesting a reversal of bleaching hierarchies of taxa over time. Our findings provide a foundation for further coral bleaching studies in a region with few published records to enable more accurate regional assessments and to follow the trajectory of future coral bleaching events.

How changes projected by climate models can inform climate adaptation and marine sanctuary management: A collaborative prototype methodology

Coral reefs are highly important ecosystems providing habitat for biodiverse marine life and numerous benefits for humans. However they face immense risks from climate change. To date, Representative Concentration Pathway (RCP) climate models have aided global discussions on possible policy responses to adapt to change, but tailored climate projections at a useful scale for environmental managers are often prohibitively expensive to produce. Our research addresses this problem by presenting a novel type of collaborative, participatory research that integrates 1) site specific climate metrics from the Community Earth System Model version 2 large ensemble (CESM2-LE), 2) ecosystem response models to determine Degree Heating Months and coral bleaching impacts, and 3) collaborative social science data from environmental manager engagement to see how managers in one of the most visited marine sanctuaries in the world are enacting adaptive governance, stewarding reefs through climate impacts of the future. Our research is valuable to decision-makers seeking opportunities for innovative policy responses to climate impacts focused on experimentation and dialogue.

Irradiance dependency of oxidative stress and coral bleaching

Irradiance dependency of oxidative stress and coral bleaching

Significant response of coral-associated bacteria and their carbohydrate-active enzymes diversity to coral bleaching

Analysis of bacterial carbohydrate-active enzymes (CAZymes) contributes significantly to comprehending the response exhibited by coral symbionts to the external environment. This study explored the impact of bleaching on the bacteria and their CAZymes in coral Favites sp. through metagenomic sequencing. Notably, principal coordinates analysis (PCoA) unveiles substantial difference in bacterial communities between bleached and unbleached corals. Proteobacteria, Actinobacteria, Acidobacteria, Bacteroidota, and Chloroflexi, exhibit noteworthy alterations during coral bleaching. CAZymes profiles in bleached coral disclosed a significant increase in Glycosyltransferases (GTs) abundance, suggesting an intensified biosynthesis of polysaccharides. Conversely, there is a marked reduction in other CAZymes abundance in bleached coral. Proteobacteria, Bacteroidota, Chlorobi, and Planctomycetota exhibit greater contributions to CAZymes in bleached corals, with Rhodobacterales, Cytophagales, Burkholderiales, Caulobacterales, and Hyphomicrobiales being the main contributors. While Acidobacteria, Actinobacteria, and Chloroflexi demonstrate higher contributions to CAZymes in unbleached corals. The changes in bacteria and their CAZymes reflect the ecological adaptability of coral holobionts when facing environmental stress. The alterations in CAZymes composition caused by bleaching events may have profound impacts on coral nutrient absorption and ecosystem stability. Therefore, understanding the dynamic changes in CAZymes is crucial for assessing the health and recovery potential of coral ecosystems.

Highest ocean heat in four centuries places Great Barrier Reef in danger

Mass coral bleaching on the Great Barrier Reef (GBR) in Australia between 2016 and 2024 was driven by high sea surface temperatures (SST)1. The likelihood of temperature-induced bleaching is a key determinant for the future threat status of the GBR2, but the long-term context of recent temperatures in the region is unclear. Here we show that the January–March Coral Sea heat extremes in 2024, 2017 and 2020 (in order of descending mean SST anomalies) were the warmest in 400 years, exceeding the 95th-percentile uncertainty limit of our reconstructed pre-1900 maximum. The 2016, 2004 and 2022 events were the next warmest, exceeding the 90th-percentile limit. Climate model analysis confirms that human influence on the climate system is responsible for the rapid warming in recent decades. This attribution, together with the recent ocean temperature extremes, post-1900 warming trend and observed mass coral bleaching, shows that the existential threat to the GBR ecosystem from anthropogenic climate change is now realized. Without urgent intervention, the iconic GBR is at risk of experiencing temperatures conducive to near-annual coral bleaching3, with negative consequences for biodiversity and ecosystems services. A continuation on the current trajectory would further threaten the ecological function4 and outstanding universal value5 of one of Earth’s greatest natural wonders.

Severe cold-water bleaching of a deep-water reef underscores future challenges for Mesophotic Coral Ecosystems

Elevated sea surface temperatures are causing an increase in coral bleaching events worldwide, and represent an existential threat to coral reefs. Early studies of Mesophotic Coral Ecosystems (MCEs) highlighted their potential as thermal refuges for shallow-water coral species in the face of predicted 21st century warming. However, recent genetic evidence implies that limited ecological connectivity between shallow- and deep-water coral communities inhibits their effectiveness as refugia; instead MCEs host distinct endemic communities that are ecologically significant in and of themselves. In either scenario, understanding the response of MCEs to climate change is critical given their ecological significance and widespread global distribution. Such an understanding has so far eluded the community, however, because of the challenges associated with long-term field monitoring, the stochastic nature of climatic events that drive bleaching, and the paucity of deep-water observations. Here we document the first observed cold-water bleaching of a mesophotic coral reef at Clipperton Atoll, a remote Eastern Tropical Pacific (ETP) atoll with high coral cover and a well-developed MCE. The severe bleaching (>70 % partially or fully bleached coral cover at 32 m depth) was driven by an anomalously shallow thermocline, and highlights a significant and previously unreported challenge for MCEs. Prompted by these observations, we compiled published cold-water bleaching events for the ETP, and demonstrate that the timing of past cold-water bleaching events in the ETP coincides with decadal oscillations in mean zonal wind strength and thermocline depth. The latter observation suggests any future intensification of easterly winds in the Pacific could be a significant concern for its MCEs. Our observations, in combination with recent reports of warm-water bleaching of Red Sea and Indian Ocean MCEs, highlight that 21st century MCEs in the Eastern Pacific face a two-pronged challenge: warm-water bleaching from above, and cold-water bleaching from below.

Corals that survive repeated thermal stress show signs of selection and acclimatization.

Climate change is transforming coral reefs by increasing the frequency and intensity of marine heatwaves, often leading to coral bleaching and mortality. Coral communities have demonstrated modest increases in thermal tolerance following repeated exposure to moderate heat stress, but it is unclear whether these shifts represent acclimatization of individual colonies or mortality of thermally susceptible individuals. For corals that survive repeated bleaching events, it is important to understand how past bleaching responses impact future growth potential. Here, we track the bleaching responses of 1,832 corals in leeward Maui through multiple marine heatwaves and document patterns of coral growth and survivorship over a seven-year period. While we find limited evidence of acclimatization at population scales, we document reduced bleaching over time in specific individuals that is indicative of acclimatization, primarily in the stress-tolerant taxa Porites lobata. For corals that survived both bleaching events, we find no relationship between bleaching response and coral growth in three of four taxa studied. This decoupling suggests that coral survivorship is a better indicator of future growth than is a coral's bleaching history. Based on these results, we recommend restoration practitioners in Hawai'i focus on colonies of Porites and Montipora with a proven track-record of growth and survivorship, rather than devote resources toward identifying and cultivating bleaching-resistant phenotypes in the lab. Survivorship followed a latitudinal thermal stress gradient, but because this gradient was small, it is likely that local environmental factors also drove differences in coral performance between sites. Efforts to reduce human impacts at low performing sites would likely improve coral survivorship in the future.

Possible toxification mechanisms of acute and chronic pentachlorophenol to Montipora digitata: Limitation of energy supply and immunotoxicity

Pentachlorophenol (PCP) is widely found in coastal environments and has various adverse effects, and its potential impact on coral reef ecosystems concerning. The scleractinian coral Montipora digitata was used for PCP stress experiments in this study. Phenotypes, physiological indicators, microbial diversity analysis and RNA sequencing were used to investigate the mechanisms underlying the responses of corals to acute and chronic PCP exposure. After 96 h of acute exposure, coral bleaching occurred at 1000 μg/LPCP and there was a significant decrease in Symbiodiniaceae density, Fv/Fm, and chlorophyll a content. Exposure to different concentrations of PCP significantly increased the content of malondialdehyde (MDA), leading to oxidative stress in corals. Chronic PCP exposure resulted in bleaching at 60 days, with the Fv/Fm significantly reduced to 0.461. Microbial diversity analysis revealed an increase in the abundance of potential pathogens, such as Vibrio, during acute PCP exposure and the emergence of the degrading bacterium Delftia during chronic PCP exposure. Transcriptional analysis showed that PCP exposure caused abnormal carbohydrate and amino acid metabolism in zooxanthella, which affected energy supply, induced immune responses, and disrupted symbiotic relationships. Corals respond to injury by boosting the expression of genes associated with signal transduction and immune response. Additionally, the expression of genes associated with environmental adaptation increased with chronic PCP exposure, which is consistent with the results of the microbial diversity analysis. These results indicate that PCP exposure might affect the balance of coral- zooxanthellae symbiosis in the stony coral M. digitata, impairing coral health and leading to bleaching.

Local conditions modulated the effects of marine heatwaves on coral bleaching in subtropical Hong Kong waters

A mass coral bleaching event occurred in the summer of 2022 in subtropical Hong Kong, driven by two marine heatwaves (MHWs) with high intensities of 1.56 and 0.86 °C above a mean climate condition, both MHWs 7 days with a short gap of 4 days during the strong La Niña year. A transect survey was conducted at nine study sites in three regions, which revealed widespread coral bleaching with bleached coral cover ranging from 2.4 to 70.3%. In situ environmental data revealed the presence of a thermocline and halocline. Local conditions, including depth and wave exposure, significantly influenced the bleaching response. Shallow-water (2–4 m) corals were primarily affected, particularly in sheltered and moderately sheltered sites that exhibited higher levels of bleached coral cover (42.97 ± 15.4% and 44.93 ± 29.4%, respectively) compared to the exposed sites (31.8 ± 5.2%). Bleaching in deep waters (4–6 m) was minimal, with only a few colonies of Goniopora at two of the three sheltered sites exhibiting bleaching (1.7 ± 1.5%). Heat stress resistance differed between coral genera. Recovery rate for four common coral genera is low for Acropora tumida. Additionally, a minor hypoxia event was found to cause mortality of non-coral benthos at a sheltered site (Sharp Island). These findings highlight the alarming impact of extreme heatwaves on subtropical coral communities and underscore the importance of monitoring coral bleaching.

Climate Change: A Caribbean Perspective

Climate change has been expedited by human activity. The Caribbean has seen the rapid progression of climate change, global warming and its harmful effects. In the Caribbean, we have an abundance of natural wonders and are considered a tourist attraction, but the progression of global warming and climate change is proving to be a threat. Guyana, which is a booming economy in the region, is developing rapidly but trying to preserve its rainforest and co-exist sustainably with the environment. It is noted that the Caribbean is experiencing more extremes of weather conditions such as hurricanes and other adverse effects of climate change including rising sea levels and bleaching of coral reefs. It is important that, as we develop, we preserve our natural attractions which encourage tourism, our diverse flora and fauna and the health of our population. Regional groups have acknowledged this and see the importance of taking action to preserve the Caribbean and its Small Island Developing States. These Small Island Developing States are disproportionately affected by climate change considering their small contribution to Green House Gases compared to the much larger developed nations. It is of paramount importance that policies and actions materialize to combat climate change and preserve health in the region. It is also crucial that we be a voice for our region bringing the phenomenon of climate change and health in the Caribbean to the global forum.

Alleviating Coral Thermal Stress via Inoculation with Quorum Quenching Bacteria.

In the background of global warming, coral bleaching induced by elevated seawater temperature is the primary cause of coral reef degradation. Coral microbiome engineering using the beneficial microorganisms for corals (BMCs) has become a hot spot in the field of coral reef conservation and restoration. Investigating the potential of alleviating thermal stress by quorum quenching (QQ) bacteria may provide more tools for coral microbial engineering remediation. In this study, QQ bacteria strain Pseudoalteromonas piscicida SCSIO 43740 was screened among 75 coral-derived bacterial strains, and its quorum sensing inhibitor (QSI) compound was isolated and identified as 2,4-di-tert-butylphenol (2,4-DTBP). Then, the thermal stress alleviating potential of QQ bacteria on coral Pocillopora damicornis was tested by a 30-day controlled experiment with three different treatments: control group (Con: 29°C), high temperature group (HT: 31°C), and the group of high temperature with QQ bacteria inoculation (HTQQ: 31°C + QQ bacteria). The results showed that QQ bacteria SCSIO 43740 inoculation can significantly mitigate the loss of symbiotic algae and impairment of photosynthesis efficiency of coral P. damicornis under thermal stress. Significant difference in superoxide dismutase (SOD) and catalase (CAT) enzyme activities between HT and HTQQ was not observed. In addition, QQ bacteria inoculation suppressed the coral microbial community beta-dispersion and improved the stability of microbial co-occurrence network under thermal stress. It was suggested that QQ bacteria inoculation can alleviate coral thermal stress via reshaping microbial interaction and maintain community stability of coral microbiome. This study provided new evidence for the probiotic function of QQ bacteria in corals, which shedding light on the development of new microbiological tools for coral reef conservation.