Acropora Pruinosa Research Articles

Coral mucus promotes the carbon metabolic potency of microorganisms in the coral reef ecosystem

AbstractCoral mucus, teeming with organic matter, releases nutrients and microorganisms, affecting element cycling and microbial communities in coral reefs. While terrestrial ecosystems exhibit well‐studied priming effects from root exudates, the influence of mucus in marine environments, particularly in coral reefs, remains underexplored. We hypothesize that coral mucus, through its nutrients and microbes, stimulates the surrounding microorganisms, regulating carbon metabolism and thus contributing to high coral reef productivity. Initially, natural samples (Acropora pruinosa mucus, seawater, and sediment) were collected for metagenomic assessment of microbial communities and functions. Results showed significant differences in microbial diversity, community structures, co‐occurrence modes, and unique functions among mucus, seawater, and sediment. Subsequent laboratory experiments demonstrated mucus's substantial influence on surrounding microorganisms. Analyses, including 16S rRNA sequencing and Eco‐plate results, revealed that mucus regulates microbial composition and activities. Quantitative gene‐chip analysis showed significant increase in the functional genes related to carbon fixation (e.g., the 3‐hydroxypropionate cycle) and degradation (e.g., pectin and hemicellulose hydrolysis) by 55.81% and 65.48%, respectively. Partial least squares path modeling identified mucus nutrients and microbial community composition as key contributors to carbon metabolic potential. This research confirms that mucus acts as a trigger, reshaping microbial profiles around corals and enhancing carbon utilization efficiency, highlighting its essential role in carbon metabolism and the maintenance of high productivity in coral reef ecosystems.

Regime shift in the northernmost coral ecosystem: decline of the threatened coral Acropora pruinosa due to grazing by Diadema setosum

Once thriving in Suruga Bay, Japan, the threatened coral species, Acropora pruinosa, faced drastic declines due to climate change and sea urchin grazing. Fourteen-years of observation (2009–2023) showed near extinction, highlighting the urgent need for conservation of corals, even in temperate zones, to preserve biodiversity.

Sexual reproduction of <i>Acropora pruinosa</i> at its northern distributional limit

Sexual reproduction of <i>Acropora pruinosa</i> at its northern distributional limit

Restoring degraded coral colony using two coral transplantation techniques: A case study from Dapeng Bay, Shenzhen, China

Three coral species, i.e. Acropora digitifera, Acropora pruinosa and Montipora peltiformis, were transplanted on 'chessboard' reef (CR) and natural substrate (NS) in Dapeng Bay, and their performance were monitored for one year. Our findings revealed that, the corals transplanted in both ways were successful and well adapted to the local environment. In comparison, corals on CR had greater growth advantage than those on NS, with corresponding height (width) growth rates of 2.03 ± 0.88 cm yr-1 to 4.82 ± 1.64 cm yr-1 (4.98 ± 1.53 cm yr-1 to 6.24 ± 2.71 cm yr-1) and 1.38 ± 0.72 cm yr-1 to 4.78 ± 2.60 cm yr-1 (1.17 ± 0.50 cm yr-1 to 4.06 ± 1.36 cm yr-1), respectively. However, the cost of CR planting technique was higher, about 1.4 times that of NS. Temperature and suspended particulate matter were the main factors affecting the health and growth of transplanted corals. This study clarified the performance of corals transplanted on CR and NS, which can provide a basis for the selection of transplantation techniques in coral reef restoration.

Unfolding the secrets of microbiome (Symbiodiniaceae and bacteria) in cold-water coral.

Recent deep-ocean exploration has uncovered a variety of cold-water coral (CWC) ecosystems around the world ocean, but it remains unclear how microbiome is associated with these corals at a molecular levels. This study utilized metabarcoding, tissue section observation, and metatranscriptomes to investigate the microbiome (Symbiodiniaceae and bacteria) of CWC species (Narella versluysi, Heterogorgia uatumani, and Muriceides sp.) from depths ranging from 260 m to 370 m. Warm-water coral (WWC) species (Acropora pruinosa, Pocillopora damicornis, and Galaxea fascicularis) were used as control groups. Results revealed that CWC host diverse bacteria and Symbiodiniaceae cells were observed in endoderm of CWC tissues. Several new candidate bacterial phyla were found in both CWC and WWC, including Coralsanbacteria, Coralqiangbacteria, Coralgsqaceae, Coralgongineae, etc. Both the 16S rRNA gene sequencing and metatranscriptomes revealed that Actinobacteria and Proteobacteria were abundant bacterial phyla in CWC. At the gene transcription level, the CWC-associated Symbiodiniaceae community showed a low-level transcription of genes involved in photosynthesis, CO2 fixation, glycolysis, citric acid cycle, while bacteria associated with CWC exhibited a high-level transcription of genes for carbon fixation via the Wood-Lijungdahl pathway, short chain fatty acids production, nitrogen, and sulfur cycles. IMPORTANCE This study shed new light on the functions of both Symbiodiniaceae and bacteria in cold-water coral (CWC). The results demonstrated that Symbiodiniaceae can survive and actively transcribe genes in CWC, suggesting a possible symbiotic or parasitic relationship with the host. This study also revealed complete non-photosynthetic CO2 fixation pathway of bacteria in CWC, as well as their roles in short chain fatty acids production and assimilation of host-derived organic nitrogen and sulfur. These findings highlight the important role of bacteria in the carbon, nitrogen sulfur cycles in CWC, which were possibly crucial for CWC survival in in deep-water environments.

Effects of heat and hyposalinity on the gene expression in Acropora pruinosa larvae

IntroductionClimate change has resulted in elevated sea surface temperature as well as increased frequency of extreme weather events, e.g. cyclones and rainstorms, which could lead to reduced seawater salinity. While temperature effects on corals have been widely examined, the combined effects of both temperature and salinity on corals, especially their early stages, remain poorly known. This study aimed to examine how the larvae of Acropora pruinosa in a marginal coral habitat, Hong Kong, respond to high temperature (+5°C ambient, HT), low salinity (26 psu, LS), and the combined effects of both stressors (HTLS).MethodsWe recorded larval survival and settlement success under different experimental treatments, and used RNA-Seq technique to compare the gene expression patterns of these larvae to understand the underlying molecular mechanism of stress responses.ResultsOur results showed that the survivorship of coral larvae was not affected in all experimental treatments, with all larvae surviving through the 72-hour period of the experiment. Yet, larval settlement was compromised under all stress treatments. The settlement rates were 39.3%, 12%, and 0% for the elevated temperature, reduced salinity, and the combined treatment, respectively, which were all significantly lower than that under the control treatment (78%). We demonstrated that low salinity (LS) triggered responsive gene sets with functions in ATP production, protein translation, and receptor for neuroactive ligands. In addition, high temperature (HT) treatment also triggered MAPK and NF-kB signaling and apoptosis in these coral larvae. The combined stressor treatment (HTLS) acted synergistically, resulting in the up-regulation of intracellular transducers that could trigger the intrinsic apoptosis pathway. This may explain the total failure in larval settlement under HTLS that could further increase larval vulnerability in the natural environment.DiscussionOur results provide new insights into the molecular responses of coral larvae and represent an essential first step in expanding ourunderstanding of the mechanisms of tolerance that may be exhibited by coral larvae exposed to multiple stressors.

Effects of microplastic combined with Cr(III) on apoptosis and energy pathway of coral endosymbiont.

The combined effect of polyethylene (PE) microplastics and chromium (Cr(III)) on the scleractinian coral Acropora pruinosa (A. pruinosa) was investigated. The endpoints analysed in this study included the endosymbiont density, the chlorophyll a + c content, and the activity of enzymes involved in apoptosis (caspase-1, caspase-3), glycolysis (lactate dehydrogenase, LDH), the pentose phosphate pathway (glucose-6-phosphate dehydrogenase, G6PDH) and electron transfer coenzyme (nicotinamide adenine dinucleotide, NAD+/NADH). During the 7-day exposure to PE and Cr(III) stress, the endosymbiont density and chlorophyll content decreased gradually. The caspase-1 and caspase-3 activities increased in the high-concentration Cr(III) exposure group. Furthermore, the LDH and G6PDH activities decreased significantly, and the NAD+/NADH was decreased significantly. In summary, the results showed that PE and Cr(III) stress inhibited the endosymbiont energy metabolism enzymes and further led to endosymbiont apoptosis in coral. In addition, under exposure to the combination of stressors, when the concentration of Cr(III) remained at 1 × 10-2mg/L, the toxic effects of heavy metals on the endosymbiont were temporarily relieved with elevated PE concentrations. In contrast, when coral polyps were exposed to 5mg/L PE and increasing Cr(III) concentrations, their metabolic activities were seriously disturbed, which increased the burden of energy consumption. In the short term, the toxic effect of Cr(III) was more obvious than that of PE because Cr(III) exposure leads to endosymbiont apoptosis and irreversible damage. This is the first study to provide insights into the combined effect of microplastic and Cr(III) stress on the apoptosis and energy pathways of coral endosymbionts. This study suggested that microplastics combined with Cr(III) are an important factor affecting the apoptosis and energy metabolism of endosymbionts, accelerating the collapse of the balance between the coral host and symbiotic endosymbiont.

Different responses of scleractinian coral Acropora pruinosa from Weizhou Island during extreme high temperature events

Different responses of scleractinian coral Acropora pruinosa from Weizhou Island during extreme high temperature events

Seasonal fluctuations in symbiotic bacteria and their role in environmental adaptation of the scleractinian coral Acropora pruinosa in high-latitude coral reef area of the South China Sea

Coral-associated bacterial communities are paramount for coral ecosystems and holobiont health. However, the role of symbiotic bacteria in the adaptation of high-latitude corals to seasonal fluctuations remains underexplored. Therefore, we used 16S rRNA-based high-throughput sequencing to analyze the symbiotic bacterial diversity, composition, and core bacterial community in high-latitude coral and explored the seasonal fluctuation characteristics of symbiotic bacterial communities. We found that bacterial richness and α-diversity changed significantly across different seasons. Additionally, the community structure recombined seasonally, with different dominant bacterial phyla and genera in different seasons. However, the symbiotic bacterial community structures of Acropora pruinosa in winter and spring were similar. Proteobacteria were the dominant bacteria in spring, autumn, and winter. In summer, the dominant bacterial taxa were Bacteroidota and Proteobacteria. Ralstonia was the dominant bacterial genus in spring and winter, whereas in autumn, BD1-7_clade was dominant. Linear discriminant analysis effect size identified 20 abundant genera between the different groups. Core microbiome analysis revealed that 12 core bacterial operational taxonomic units were associated with A. pruinosa in all seasons, seven of which varied with the seasons, changing between dominant and rare. Distance-based redundancy and variation partitioning analyses revealed that sea surface temperature was the major contributor of variation in the microbial community structure. We hypothesized that the high diversity and abundance of symbiotic bacteria and the increase in Prosthecochloris abundance in coral in summer can help A. pruinosa maintain its physiological functions, ameliorating the negative physiological effects of the decrease in Symbiodiniaceae density under high-temperature stress. Thus, the rapid reorganization of the symbiotic bacterial community structure and core microflora in different seasons may allow the corals to adapt to large seasonal environmental fluctuations. In conclusion, seasonal variation of bacteria plays an important role in coral adaptation to large environmental fluctuations.

Cytogenetic markers using single-sequence probes reveal chromosomal locations of tandemly repetitive genes in scleractinian coral Acropora pruinosa

The short and similar sized chromosomes of Acropora pose a challenge for karyotyping. Conventional methods, such as staining of heterochromatic regions, provide unclear banding patterns that hamper identification of such chromosomes. In this study, we used short single-sequence probes from tandemly repetitive 5S ribosomal RNA (rRNA) and core histone coding sequences to identify specific chromosomes of Acropora pruinosa. Both the probes produced intense signals in fluorescence in situ hybridization, which distinguished chromosome pairs. The locus of the 5S rDNA probe was on chromosome 5, whereas that of core histone probe was on chromosome 8. The sequence of the 5S rDNA probe was composed largely of U1 and U2 spliceosomal small nuclear RNA (snRNA) genes and their interspacers, flanked by short sequences of the 5S rDNA. This is the first report of a tandemly repetitive linkage of snRNA and 5S rDNA sequences in Cnidaria. Based on the constructed tentative karyogram and whole genome hybridization, the longest chromosome pair (chromosome 1) was heteromorphic. The probes also hybridized effectively with chromosomes of other Acropora species and population, revealing an additional core histone gene locus. We demonstrated the applicability of short-sequence probes as chromosomal markers with potential for use across populations and species of Acropora.

High Clonality and Geographically Separated Cryptic Lineages in the Threatened Temperate Coral, Acropora pruinosa

Acropora pruinosa is a threatened zooxanthellate scleractinian coral that is distributed in the temperate areas along the coastline of Japan and the northern area of the South China Sea. Since A. pruinosa propagates both asexually and sexually, assessing clonal diversity and genetic connectivity among populations is important for conservation. In addition, high morphological variations in the field create confusion during species identification. To examine the existence of hidden genetic lineages, clonality, and genetic connectivity of A. pruinosa for conservation, we applied microsatellite analysis. Clustering analysis indicated two distinct geographically separated genetic lineages: one is distributed in the west, and the other is distributed in the east. The two lineages co-existed in Nishidomari, Kochi. There was no obvious difference in morphological characteristics between the two lineages. Although the factors influencing the observed distribution patterns remain unknown, there is a possibility that the two lineages might have diverged somewhere in the north-western Kyushu and north-eastern Pacific coast habitats in the past, and then periodically colonized the current habitats. A low clonal diversity was observed in most of the populations, indicating a high rate of asexual reproduction associated with their branching morphologies. In addition, there are strong genetic structuring in this species, indicating weak connectivity among populations. These results indicated a low larval dispersal potential among populations and that populations are basically sustained by a high rate of clone propagation and self-seeding. The existence of cryptic lineages and genetically isolated populations with high clonality emphasized the importance of conservation of A. pruinosa.

First record of synchronous coral spawning in a marginal coral community in Shenzhen, China

Here we present the first documentation of a synchronous coral spawning event in a marginal coral community in Shenzhen. Acropora pruinosa was observed spawning for seven consecutive nights after the full moon, and Platygyra carnosa was observed spawning on the eighth and ninth nights after the full moon.

Karyotypic mosaicism and molecular cytogenetic markers in the scleractinian coral Acropora pruinosa Brook, 1982 (Hexacorallia, Anthozoa, Cnidaria)

Molecular cytogenetic investigation was carried out on the scleractinian coral, Acropora pruinosa (A. pruinosa). Conventional Giemsa staining techniques for karyotyping, such as G- and C-banding, were conducted. Karyotype analysis showed mosaicism of cells with two different chromosome numbers, 28 and 29, in the same embryo. The C-band positive portions appeared on the centromeres of most chromosomes and along the entire length of the unpaired chromosome 15 in cells with 29 chromosomes. Fluorescence in situ hybridization (FISH) revealed that the loci of rRNA genes (rDNA), 5S and 18S/28S, were located on chromosomes 4 and 2, respectively. Whole genome hybridization (WGH) with sperm DNA showed distinct signals not only on all centromeric regions but also on a whole unpaired chromosome 15. Comparative genomic hybridization (CGH) using DNAs from sperm and unfertilized eggs revealed that the unpaired chromosome 15 has sperm-specific DNA sequences. We therefore hypothesized the existence of a sex-related chromosome in A. pruinosa. In this study, we have presented a tentative karyotype of this coral, based on banding results, and described FISH, WGH, and CGH results. Moreover, we successfully cloned and sequenced three clones; AP-5S for 5S rDNA, AP-18S for 18S/28S rDNA, and AP-unpaired chromosome 15q for the unpaired chromosome 15-specific DNA. These molecular cytogenetic approaches will help establish a more exact karyotype of corals and promote understanding of coral genetics, including chromosome evolution. These findings will help to verify the method of classification of complex scleractinian corals.

Potential molecular traits underlying environmental tolerance of Pavona decussata and Acropora pruinosa in Weizhou Island, northern South China Sea

Coral species display varying susceptibilities to biotic or abiotic stress. To address the causes underlying this phenomenon, we profiled the Symbiodiniaceae clade type, bacterial communities and coral transcriptome responses in Pavona decussata and Acropora pruinosa, two species displaying different environmental tolerances in the Weizhou Island. We found that C1 was the most dominant Symbiodiniaceae subclade, with no difference detected between A. pruinosa and P. decussata. Nevertheless, P. decussata exhibited higher microbial diversity and significantly different community structure compared with that of A. pruinosa. Transcriptome analysis revealed that coral genes with significantly high expression in P. decussata were mostly related to immune and stress-resistance responses, whereas, those with significantly low expression were metabolism-related. We postulate that the higher tolerance of P. decussata as compared with that of A. pruinosa is the result of several traits, such as higher microbial diversity, different dominant bacteria, higher immune and stress-resistant response, and lower metabolic rate.

Thermal acclimation increases heat tolerance of the scleractinian coral Acropora pruinosa

Field ecological observations indicate that scleractinian coral exposed to early thermal stress are likely to develop higher tolerance to subsequent heat stress. The causes of this phenomenon, however, remain enigmatic. To unravel the mechanisms underlying the increased heat tolerance, we applied different thermal treatments to the scleractinian coral Acropora pruinosa and studied the resulting differences in appearance, physiological index, Symbiodiniaceae and bacterial communities, and transcriptome response. We found that early heat stress improved the thermal tolerance of the coral holobiont. After thermal acclimation, the community structure and symbiotic bacterial diversity in the microbiota were reorganized, whereas those of Symbiodiniaceae remained stable. RNA-seq analysis revealed that the downregulated coral host genes were mainly involved in pathways relating to metabolism, particularly the nitrogen metabolism pathway. This indicates that thermal acclimation led to decrease in the metabolism level in the coral host, which might be a self-protection mechanism. We suggest that thermal acclimation may increase scleractinian coral thermal tolerance by slowing host metabolism, altering the dominant bacterial population, and increasing bacterial diversity. This study offers new insights into the adaptive potential of scleractinian coral to heat stress from global warming.

Corallivory plays a limited role in the mortality of new coral recruits in Hong Kong marginal coral communities

Coral recruitment plays a vital role in mediating adult coral population structure as well as in promoting coral reef recovery after disturbances. As one of the most delicate life stages of coral, coral recruits were reported to be sensitive to several environmental, physical and biological stresses. This study aimed to examine the effects of Drupella corallivory on coral recruits of the massive Platygyra acuta and branching Acropora pruinosa in Hong Kong. Coral recruits were induced to settle on settlement tiles (R tiles). These tiles, alongside with tiles without coral recruits (NR tiles) and brand new tiles (NE tiles), were used in the prey-choice experiment to test the attractiveness of coral recruits to Drupella. The overall attractiveness of different types of tiles to the snails was low, and more Drupella snails were found on NR tiles instead of the R tiles. Effect of Drupella corallivory was also evaluated by counting the number of recruits lost after a movement experiment. The results revealed that only <10% of coral recruits were removed by Drupella, and similar outcomes were also obtained when herbivorous gastropods Tectus pyramis and Euplica scripta were used. This suggested that the loss of coral recruits due to corallivorous gastropods was not any greater than that due to the herbivores. All these results indicate that coral recruits were not attractive to Drupella, and the effect posed by this corallivore gastropod on the survival of coral recruits was limited.

The complete mitochondrial genome of the Acropora pruinosa

In this study, the complete mitogenome sequence of stony coral, Acropora pruinosa (Scleractinia), has been decoded for the first time by next generation sequencing and genome assembly. The assembled mitogenome, consisting of 18,480 bp, has unique 13 protein-coding genes (PCGs), three transfer RNAs, and two ribosomal RNAs genes. The complete mitogenome of Acropora pruinosa showing 99% identities to Acropora nasuta. The complete mitogenome provides essential and important DNA molecular data for further phylogenetic and evolutionary analyses for coral phylogeny.

The northern limit of corals of the genus Acropora in temperate zones is determined by their resilience to cold bleaching.

The distribution of corals in Japan covers a wide range of latitudes, encompassing tropical to temperate zones. However, coral communities in temperate zones contain only a small subset of species. Among the parameters that determine the distribution of corals, temperature plays an important role. We tested the resilience to cold stress of three coral species belonging to the genus Acropora in incubation experiments. Acropora pruinosa, which is the northernmost of the three species, bleached at 13 °C, but recovered once temperatures were increased. The two other species, A. hyacinthus and A. solitaryensis, which has a more southerly range than A. pruinosa, died rapidly after bleaching at 13 °C. The physiological effects of cold bleaching on the corals included decreased rates of photosynthesis, respiration, and calcification, similar to the physiological effects observed with bleaching due to high temperature stress. Contrasting hot bleaching, no increases in antioxidant enzyme activities were observed, suggesting that reactive oxygen species play a less important role in bleaching under cold stress. These results confirmed the importance of resilience to cold stress in determining the distribution and northern limits of coral species, as cold events causing coral bleaching and high mortality occur regularly in temperate zones.

Twenty-five years of change in scleractinian coral communities of Daya Bay (northern South China Sea) and its response to the 2008 AD extreme cold climate event

Coral reefs worldwide are becoming increasingly and detrimentally impacted upon by a variety of factors including significant climate changes, such as global warming and increased El Nino-Southern Oscillation activity. Generally, the persistence of coral reefs, especially at low-latitudes, is governed, in part, by sea surface temperatures not exceeding the critical limit (similar to 30A degrees C) at which mass mortality can occur. Thus, it is thought that corals living at high-latitudes (i.e., currently cooler sea surface temperatures) will likely respond more favourably to hypothesized future temperature increases than corals living at low-latitudes (i.e., currently warmer sea surface temperatures). Consequently, high-latitude coral communities may have the potential to act as regions of refugia for many coral species in the face of potential future global warming. The Daya Bay (22A degrees 31'aEuro22A degrees 50'N), northern South China Sea, contains several high-latitude non-reefal coral communities and represents one of the most northerly distributions of scleractinian corals within the region. Significantly, Daya Bay has experienced dramatic warming in both air and sea surface temperatures throughout the past 50 years. In this paper, we analyze 25 years of change in the Daya Bay coral communities, based both on historic surveys and our latest 2006-2008 regional ecological surveys. Our results suggest that, contrary to predictions, there have been significant declines in coral cover within the Daya Bay during the past 25 years (i.e., 76.6% coral cover in 1983/1984 to only 15.3% coral cover by 2008). Such changes also reflect a significant shift in the most abundant coral species, from Acropora pruinosa to Favites abdita. Most of the modern coral communities became established between 15 and 30 years ago, corresponding to a period of increased winter sea surface temperature. However, very few colonies have become established within the last 15 years, despite a more intense period of warming. By taking into account additional factors, we hypothesize that direct anthropogenic impacts, rather than climatic events, have both restricted the development, and drove the decline, of Daya Bay coral communities in the last 15 years. The Daya Bay has also been subjected to occasional extreme cold events during the past 50 years, with the most recent occurring in early 2008 (13 January-13 February). During the 2008 cold event, the lowest air temperature reaches only 6.6A degrees C, and the mean sea surface temperature for February fall to < 14A degrees C, including six continuous days at 12.3A degrees C. Significantly, the sea surface temperatures fall below the hypothesized critical lower temperature threshold (similar to 13A degrees C) that commonly leads to mass mortality in scleractinian coral communities. Surprisingly, our coral community surveys, conducted both before (August 2007) and after (late February 2008) the extreme 2008 cold event, demonstrate that the Daya Bay coral ecosystems are barely impacted upon during the cold period. Those observations suggest that the Daya Bay scleractinian coral communities have developed adaptations to low sea surface temperatures. Overall, our data support the hypothesis that high-latitude coral communities, such as Daya Bay, have the potential to act as areas of refugia for scleractinian corals in the advent of potential future global warming.

Restriction Fragment Length Polymorphism Analysis of Large Subunit rDNA of Symbiotic Dinoflagellates from Scleractinian Corals in the Zhubi Coral Reef of the Nansha Islands

AbstractZooxanthellae are very important for the coral reef ecosystem. The diversity of coral hosts is high in the South China Sea, but the diversity of zooxanthellae has not yet been investigated. We chose the Zhubi Coral Reef of the Nansha Islands as the region to be surveyed in the present study because it represents a typical tropical coral reef of the South China Sea and we investigated zooxanthellae diversity in 10 host scleractinian coral species using polymerase chain reaction (PCR) of the large subunit rRNA and restriction fragment length polymorphism (RFLP) patterns. Pocillopora verrucosa, Acropora pelifera, Acropora millepora, Fungia fungites, Galaxea fascicularis, and Acropora pruinosa harbor Clade C, Goniastrea aspera harbors Clade D, and Acropora formosa harbors Clades D and C. Therefore, the Clade C is the dominant type in the Zhubi Coral Reef of the Nansha Islands. Furthermore, the results of the present also disprove what has been widely accepted, namely that one coral host harbors only one algal symbiont. The coral‐algal symbiosis is flexible, which may be an important mechanism for surviving coral bleaching. Meanwhile, on the basis of the results of the present study, we think that Symbiodinium Clade D may be more tolerant to stress than Symbiodinium Clade C.(Managing editor: Ya‐Qin Han)