Coral Ecosystems Research Articles

Recent trends and biases in mesophotic ecosystem research.

Mesophotic ecosystems (approx. 30-150 m) represent a significant proportion of the world's oceans yet have long remained understudied due to challenges in accessing these deeper depths. Owing to advances in underwater technologies and a growing scientific and management interest, there has been a major expansion in research of both (sub)tropical mesophotic coral ecosystems and temperate mesophotic ecosystems. Here, we characterize the recent global trends in mesophotic research through an updated release of the 'mesophotic.org' database (www.mesophotic.org) where we reviewed and catalogued 1500 scientific publications. In doing so, we shed light on four major research biases: a gross imbalance in (a) the geographical spread of research efforts, differences in (b) the focal depth range and (c) research fields associated with study organisms and research platforms, and (d) the lack of temporal studies. Overall, we are optimistic about the future of mesophotic research and hope that by highlighting current trends and imbalances, we can raise awareness and stimulate discussion on the future directions of this emerging field.

An Improved RNA Extraction Method for Octocorals and Its Application in Transcriptome Analysis of Dark-Induced Bleaching Octocoral.

Octocorals, vital components of reef ecosystems, inhabit various marine environments across diverse climate zones, spanning from tropical shallows to frigid deep-sea regions. Certain octocoral species, notably Lobophytum and Sinularia, are particularly intriguing due to their production of diverse metabolites, warranting continuous investigation. Although octocorals played the roles in coral ecosystems, the studies are rare in comparison to scleractinian corals, especially in transcriptomic and genomic data. However, RNA extraction was massively interfered by the polysaccharides and secondary metabolites produced from octocoral holobiont. For this purpose, five lysis buffer systems and two extraction processes were examined for the RNA extraction efficiency in octocorals. We found CTAB/10%SDS as a new method for RNA extraction from six different octocoral genera. Furthermore, our new method is enable to extract RNA with good quality for downstream application such as quantitative PCR and RNA sequencing. Finally, comparative transcriptomic analysis between healthy octocorals and those dark-induced bleaching corals in Lobophytum hsiehi revealed extracellular matrix and immunity-related genes may play the important roles in coral-symbiodinium symbiosis. We believe that this study's findings and the developed RNA extraction method will serve as valuable references for future research, particularly in octocorals.

Using underwater mini-ROV for coral eDNA survey: a case study in Okinawan mesophotic ecosystems

AbstractMesophotic coral ecosystems (MCEs) are light-dependent communities occurring at depths of 30–150 m. They have been suggested to serve as refuge against thermal stress during heat waves for some coral species. Recent studies on MCEs have revealed a high diversity of communities, some unique, and that these ecosystems are far from being immune to anthropogenic threats. However, the depths at which these ecosystems are found make their exploration and study challenging. Consequently, most suitable environments for MCEs remain unexplored. To facilitate the detection and characterization of MCEs, we improved the methodology for mesophotic scleractinian survey by environmental DNA (eDNA) metabarcoding analysis using seawater collected by underwater mini-Remote Operated Vehicle (mini-ROV). We tested this improved approach at upper mesophotic sites in Okinawa, Japan, with different corals dominating the communities (i.e., Alveopora-dominated, Seriatopora-dominated, and Acropora-dominated communities). Despite the proximity of the different sites, our eDNA metabarcoding analyses detected the dominant coral genera specific to each site. In addition, this study detected numerous other genera present at these sites, including Acropora, Pachyseris, Galaxea, Lobophyllia, Montipora, Pocillopora, Porites, and others. Therefore, this study might support a new technical gate for comprehensive survey of MCEs using eDNA samples collected by underwater mini-ROV, although further technical improvement is required for quantitative estimation.

Mortality patterns and recovery challenges in Millepora alcicornis after mass bleaching event on Northeast Brazilian reefs

Coral reefs are suffering globally from the increased frequency and intensification of thermal anomalies, caused by anthropogenic climate change, leading to major mass bleaching events over the past three decades. Environmental factors, including temperature, geomorphology, interspecific competition, protection status and local settings, can modulate the severity of bleaching and the subsequent survival capacity of corals and hydrocorals after mass bleaching events. However, the complexity of environmental factors interacting over fine-scale spatial-temporal scales is still a major gap in understanding coral bleaching events of South Atlantic reefs. Here, we examined mortality and recovery patterns of the predominant hydrocoral species Millepora alcicornis after a mass bleaching event at the Northeastern coast of Brazil in 2019–2020. The ecological impact was evaluated by analyzing spatial factors, coral morphology, protection status and mortality rates in combination with the subsequent recovery potential influenced by overgrowth competition of dominant benthic organisms. The results indicate that hydrocorals located in proximity to the shore and shallow depths were more vulnerable with mortality rates of up to 90%, presumably related to higher light and temperature fluctuations. A total coral cover loss of approx. 50% was estimated for M. alcicornis within the study area and dead skeletons were overgrown by algal turfs and crustose coralline algae with the former being the predominant colonizer. In summary, our findings reveal fin-scale heterogeneous spatial vulnerability within the same coastal reef complex, indicating zones of high coral mortality. The described heterogeneous spatial vulnerability of the studied reef complex is an important factor to be considered in coral reef restauration and management plans to secure coral ecosystem services for the coming decades.

Elasmobranch assemblage structure on protected high-latitude coral reefs of southeast Africa

High-latitude coral reefs (HLCRs) are unique ecosystems with diverse biological assemblages, including many low latitude species on their distribution margins. These ecosystems are threatened by fisheries exploitation, habitat destruction and climate change; however, relative to low latitude coral ecosystems, our understanding of their structure and functioning is limited. This is particularly true for sharks and rays. In this study, we used baited remote underwater stereo-video systems to determine the effect of habitat and management on the assemblage structure of elasmobranchs on the HLCRs of southern Africa (26-28°S; iSimangaliso Marine Protected Area [MPA], South Africa, and the adjoining Ponta do Ouro Partial Marine Reserve, Mozambique). We recorded a total of 12 species of shark (142 individuals) and 9 species of ray (40 individuals) over 2 brief time frames (November 2016 and June 2017). All species were tropical with many on the southern limit of their known distributions. Sharks increased in diversity with depth and showed a preference for the reef and mosaic habitats, relative to sand. The occurrence of rays was predominantly influenced by the presence of low relief habitats. These findings highlight the need for MPAs to encompass both sand and reef habitats over broad depth ranges to effectively protect elasmobranch assemblages. We found evidence to support the high average abundance and diversity of sharks and rays within MPAs of South Africa and southern Mozambique. The results highlight the importance of marginal HLCRs, particularly those within MPAs, for the management and conservation of tropical elasmobranch species.

Shallow corals acclimate to mesophotic depths while maintaining their heat tolerance against ongoing climate change

Global warming poses a significant threat to coral reefs. It has been assumed that mesophotic coral ecosystems (MCEs, 30 to 150 m depths) may serve as refugia from ocean warming. This study examined the acclimation capacity and thermal tolerance of two shallow coral species, Porites cylindrica and Turbinaria reniformis, transplanted to mesophotic depths (40 m) for 12 months. Fragments from 5 and 40 m were exposed to control (28 °C), moderate (30 °C), and high (32 °C) temperatures over 14 days. MCE-acclimated fragments showed higher thermal thresholds and survival rates, delayed onset of bleaching, and less decline in photosynthesis efficiency (Fv/Fm) compared to shallow fragments. Both species maintained high thermal tolerance despite prolonged exposure to cooler temperatures of mesophotic depth. These findings suggest that low light intensity in MCEs can act as a modulator of bleaching, supporting the potential of these ecosystems as refugia for shallow corals in a rapidly changing world.

Identification and Analysis of the Nutrition Value of Black Teripang (Holothuriaedulis) and Sand Teripang (Holothuria Scabra) In the Waitiu Flow of Lewolema District

Indonesia is a country with a large area of ​​water, with enormous potential for marine biodiversity which is useful as food, pharmaceuticals and cosmetics. There are several marine biota that produce secondary metabolites that are beneficial to humans, including microorganisms, blue green algae, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs and sea cucumbers (echinoderms). Sea cucumbers are marine animals classified in the phylum Echinodermata, class Holothuroidea. This animal lives on sandy substrates or can be found in coral ecosystems. Sea cucumbers have complete and quite high nutritional content, but the existence of sea cucumbers with a high population in East Flores Regency has not been utilized properly. This study aims to identify and analyze the nutritional content of Sand Sea Cucumber (Holothuria Scabra) and Black Sea Cucumber (Holothuria Edulis). Identification is based on morphology and body color and spicules of the dorsal integument tissue, while the analysis of nutritional value includes water content and ash content using the gravimetric method, protein content using the Kjeldahl method, fat content using the Soxhlet method and carbohydrate content using the by difference method. The results of the study showed that the nutritional content of Sand Sea Cucumber (Holothuria Scabra) was 5.472% water content, 51.056% ash content, 27.072% protein content, 1.449% fat content and 20.424% carbohydrate content, while the nutritional content of Black Sea Cucumber (Holothuria Edulis) was 6.214% water content, 18.864% ash content, 51.636% protein content, 0.659% fat content and 28.841% carbohydrate content.

Cold-water coral ecosystems along the Apulian coasts: Biodiversity and urgency of conservation measures in the Anthropocene

Information on the biodiversity of benthopelagic fauna of deep-sea Vulnerable Marine Ecosystem (VMEs) network along the Apulian margin (central Mediterranean Sea) is reported in this paper. Data were collected using two low impact sampling tools between 2010 and 2019 in 3 VMEs characterised by cold-water corals (CWC): Bari Canyon (BC), off Monopoli (Mn) and off Santa Maria di Leuca (SML). Using longline, a total of 53 deployments were carried out between 314 and 650 m depth for a total time of about 217 fishing hours, whereas using the baited lander MEMO (Marine Environment MOnitoring system) a total of 31 deployments were carried out between 427 and 792 m, for a total of 223 h of video record. A total of 60 taxa were recorded: 9 cephalopods (only one species was collected with longline), 14 crustaceans (2 species were collected with longline), 13 Chondrichthyes (11 collected with longline and seven species observed with baited lander) and 24 Osteichthyes (15 sampled with longline and 16 recorded by baited lander). The similarities in species observed between the VMEs characterize the network of VMEs along Apulian margin, whereas the detected differences are due to the different abundance of some species, such as Galeus melastomus Helicolenus dactylopterus and Phycis blennoides. In all three VMEs were found commercial and vulnerable/endangered species as well as large and sexually mature individuals of cartilaginous and teleost fishes. This presence confirms that the network of VMEs along Apulian margin can act as a network of refuge areas for species threatened by anthropogenic pressures such as fishing activities carried out on the muddy seabeds surrounding VMEs.

Beautoide A, an Anti-Osteoclastogenic Sterol from Beauveria sp. NBUF147 Associated with an Irciniidae Sponge from the Marine Mesophotic Zone.

Mesophotic coral ecosystems (MCEs), located at depths ranging from 30-150 m, host some of the most diverse yet least explored marine bioresources, particularly significant for the discovery of new bioactive molecules. The fungus Beauveria sp. NBUF147, associated with an Irciniidae sponge from the mesophotic zone at a depth of 82 m, underwent chemical investigation that led to the identification of one new sterol, beautoide A (1), and one reported sterol, 3β,5α,9α-trihydroxy-(22E,24R)-ergosta-7,22-dien-6-one (2). Their structures were determined from analysis of spectroscopic data and X-ray crystallography. Evaluation of biological activity in prednisolone-induced osteoporotic zebrafish showed that 1 was anti-osteoclastogenic in vivo at 3.0 μM.

Artificial Intelligence-Assisted Environmental DNA Metabarcoding and High-Resolution Underwater Optical Imaging for Noninvasive and Innovative Marine Environmental Monitoring

To effectively protect the marine environment, it is crucial to establish effective environ mental monitoring platforms. Traditional marine environmental monitoring methods heavily rely on morphological identification and field expertise, with the sampling process being disruptive and potentially destructive to vulnerable marine environments. In light of emerging biomonitoring needs and biodiversity declines, we reviewed the urgently needed, ongoing advances in developing effective, noninvasive, and innovative monitoring methods and systems to examine the complex marine environment for better strategic conservation and protection, using the coral ecosystem as one of the representative forefront examples in marine protection. This review summarizes current trends and efforts in transitioning into more standardizable and automatable utilizations of environmental DNA metabarcoding-based monitoring strategies and high-resolution underwater optical imaging monitoring systems as two of the promising pillars for the next generation of noninvasive biomonitoring and associated applications. The assistance of artificial intelligence for environmental DNA metabarcoding and high-resolution underwater optical imaging into an empowered, all-rounded monitoring platform for enhanced monitoring capacity is discussed as a highly potent direction for future research exploration. This review will be a cornerstone reference for the future development of artificial intelligence-assisted, noninvasive, and innovative marine environmental monitoring systems.

Analysis on Coral Bleaching (Soft/Hard Coral) and Coral Ecosystem Restoration Strategies—Linkage to Sustainable Industries and Economic Valuation†

Among marine ecosystems, coral reefs play crucial roles in terms of ecological functions such as biodiversity protection and coastal protection and have significant economic value, estimated at approximately 2.7 trillion USD per year. However, the current state of coral reefs is alarming, with more than 93% of coral ecosystems being damaged primarily by human activity and climate change. In line with UN Sustainable Development Goals 13 and 14, this research aims to analyze coral bleaching in soft corals in Korea and coral reefs in Malaysia through field surveys and interviews to assess their current conditions. This study also explores strategies for the restoration of coral ecosystems, utilizing economic valuation methods such as the Toolkit for Ecosystem Service Site-Based Assessment (TESSA). Despite the limitations of applying a landscape-focused methodology to the marine environment and the lack of available data, this study emphasizes the importance of sustainable tourism and collaborative educational curricula involving governmental research institutes, universities, NGOs, and divers. These efforts are inspired by interactions with the Borneo Marine Research Institute (BMRI) at Sabah University and the Reef Check Center in Malaysia.

Unraveling the physiological responses of morphologically distinct corals to low oxygen

Background Low oxygen in marine environments, intensified by climate change and local pollution, poses a substantial threat to global marine ecosystems, especially impacting vulnerable coral reefs and causing metabolic crises and bleaching-induced mortality. Yet, our understanding of the potential impacts in tropical regions is incomplete. Furthermore, uncertainty surrounds the physiological responses of corals to hypoxia and anoxia conditions. Methods We initially monitored in situ dissolved oxygen (DO) levels at Kham Island in the lower Gulf of Thailand. Subsequently, we conducted a 72-hour experimental exposure of corals with different morphologies—Pocillopora acuta, Porites lutea, and Turbinaria mesenterina—to low oxygen conditions, while following a 12/12-hour dark/light cycle. Three distinct DO conditions were employed: ambient (DO 6.0 ± 0.5 mg L−1), hypoxia (DO 2.0 ± 0.5 mg L−1), and anoxia (DO < 0.5 mg L−1). We measured and compared photosynthetic efficiency, Symbiodiniaceae density, chlorophyll concentration, respiratory rates, primary production, and calcification across the various treatments. Results Persistent hypoxia was observed at the study site. Subsequent experiments revealed that low oxygen levels led to a notable decrease in the maximum quantum yield over time in all the species tested, accompanied by declining rates of respiration and calcification. Our findings reveal the sensitivity of corals to both hypoxia and anoxia, particularly affecting processes crucial to energy balance and structural integrity. Notably, P. lutea and T. mesenterina exhibited no mortality over the 72-hour period under hypoxia and anoxia conditions, while P. acuta, exposed to anoxia, experienced mortality with tissue loss within 24 hours. This study underscores species-specific variations in susceptibility associated with different morphologies under low oxygen conditions. The results demonstrate the substantial impact of deoxygenation on coral growth and health, with the compounded challenges of climate change and coastal pollution exacerbating oxygen availability, leading to increasingly significant implications for coral ecosystems.

Microplastic pollution in tropical coral reef ecosystems from the coastal South China Sea and their impacts on corals in situ

Coral reefs possess extremely high ecological value in tropical and subtropical waters worldwide. Microplastics as emerging and pervasive pollutants pose a great threat to the health of coral ecosystems. However, in situ studies on microplastics pollution and its impacts in coral ecosystems globally are limited. The occurrence characteristics of microplastics in the environment mediums and reef-dwelling organisms were investigated in coral reef areas from the southern Hainan Island, and the impacts of microplastics on corals in situ were evaluated in this study. Average microplastics abundance was 9.48 items L-1 in seawater, 190.00 items kg-1 in sediment, 0.36 items g-1 in coral, 1.50 items g-1 in shellfish, 0.48 items g-1 in fish gill, and 1.71 items g-1 in fish gastrointestinal tract. The prevalent microplastics in the above samples were characterized as being less than 1000 µm in size, fibrous, and transparent, with predominant polymer types as polyethylene terephthalate, polypropylene, polyethylene, and rayon. The microplastic enrichment capacity of different corals varied (Pocillopora >Acropora >Sinularia). Notably, microplastics were more abundant on the surface of corals compared to their interiors, with distinct characteristics observed, including larger-sized (>500 µm) and fiber-shaped polyethylene terephthalate microplastics on the surface and smaller-sized (20–200 µm) fragmented polyethylene microplastics within coral interiors. Furthermore, the investigation showed species-specific impacts of microplastics on corals in situ, including photosynthetic activity of photosymbionts and antioxidant and immune activities of corals. Furthermore, the ecological risks of microplastics were minor across most environmental media in the studied areas, with exceptions in the bottom seawater and surface sediment of YLW, which exhibited extreme and medium risk levels, respectively. Coral risk levels were generally medium, except for dangerous levels in DDH and high levels in LHT. The potential sources of microplastics in the marginal reefs of southern Hainan Island were primarily tourism, residential, and fishing activities.

Synergistic impacts of reduced grazing and nutrient enrichment on biofouling assemblages in a degraded coral reef ecosystem

While the coral reefs in the Persian Gulf have adapted to withstand some of the most challenging environmental conditions, overfishing and eutrophication can disrupt the structure of their associated biofouling assemblages. In the present study, the effects of reduced grazing pressure and eutrophication on the assemblage structure of biofouling functional groups in the coral reefs of Hengam Island (Persian Gulf) was investigated using a 21-month manipulative experiment utilizing settlement tiles. A total of 40 biofouling taxa were identified, none of which belonged to reef-building corals or the key facilitators of coral settlement. The effect of grazers on cover percentage was overshadowed by nutrient enrichment; suggesting a bottom-up control mechanism rather than top-down regulation in the coral ecosystem of the island. Our results suggest that grazers can reduce the coral-competing functional groups only in the absence of other confounding factors such as nutrient pollution

The relationship between coral fish diversity and ecosystem services as an added value for the sustainable development: Evidence in Tanjung Lesung SEZ, Banten Province, Indonesia

Abstract This study aims to explore the relationship between the diversity of coral fish resources and ecosystem services as added value in the development of sustainable Special Economic Zones (SEZs). The existence of SEZs has become an economic focal point, making the balance of the natural environment increasingly crucial to support long-term economic growth. Data collection for this research was conducted through field surveys to assess the diversity of coral fish resources, including species, abundance, and distribution in Tanjung Lesung. The data was further analyzed to determine the added value of ecosystem services to SEZ development, which includes provisioning services and cultural services. The results of the study revealed a significant relationship between the diversity of coral fish resources and ecosystem services in the area. High levels of species and resources diversity positively contribute to food availability for communities, as well as enhancing cultural services, such as tourism. Additionally, coral fish naturally plays a vital role in maintaining ecosystem balance and ensuring the survival of other species in the food chain. The findings of this research provide a deeper understanding of the importance of sustainability and governance of coral fish resources in supporting the development of SEZs. This study also serves as a foundation for policy planning that focuses on responsible and sustainable utilization of coral fish resources to achieve balanced long-term economic development in harmony with aspect of environmental conservation.

Differential strategies developed by two light-dependent scleractinian corals to extend their vertical range to mesophotic depths

Mesophotic coral ecosystems are characterised by the presence of photosynthetic scleractinian corals despite the decreasing amounts of light available with depth. To better understand physiological strategies across a broad depth gradient, we studied the biological trait responses of Pocillopora cf. verrucosa from 6 to 60 m depth and Pachyseris “speciosa” spp. from 20 to 90 m depth at four islands of French Polynesia. Specifically, we characterised associated Symbiodiniaceae communities, photophysiological traits (Symbiodiniaceae density and chlorophyll concentrations), micro-morphology and trophic plasticity (autotrophy vs heterotrophy inferred from stable isotopes). Our results showed that both taxa can live at mesophotic depths without significant genetic structuring in their generic Symbiodiniaceae communities, mainly composed of Cladocopium and Durusdinium. Yet, the prevalence of Symbiodiniaceae ITS2 profiles revealed location-based variations that sometimes interact with depth and highlight putative shallow- or depth-tolerant taxa. For both taxa, symbiont density and chlorophyll pigment concentrations increased with increasing depth. We also found a change in their skeletal micro-morphology with an increase in the inter-corallite distance for Pocillopora cf. verrucosa and a decrease in the height of septa for Pachyseris “speciosa” spp. with depth. Finally, we found no isotopic evidence of switching to a more heterotrophic diet as their primary energy source, although host–tissue δ13C ratios became more negative with depth in both corals. Overall, our findings show similarity (across the two species) and species-specific strategies (biological trait patterns with increasing depth) underlying the capacity of symbiotic scleractinian corals to live in low-light environments.

Community structure and biomass of reef fish concerning coral cover in Sempu Strait, East Java, Indonesia

Abstract. Isdianto A, Ariefandi MF, Asadi MA, Yamindago A, Setyawan FO, Bintoro G, Setyanto A, Lelono TD, Tumulyadi A, Adhihapsari W, Setyoningrum D, Fathah AL, Putri BM, Supriyadi, Luthfi OM. 2024. Community structure and biomass of reef fish concerning coral cover in Sempu Strait, East Java, Indonesia. Biodiversitas 25: 3376-3385. Reef fishes were used as bioindicators of biodiversity in coral reef ecosystems. However, coral cover and reef fish abundance around Sempu Strait tended to decrease. The study aims to obtain reef fish's community structure and biomass and their correlation to coral cover. We observed significant variability in reef fish populations through bi-monthly monitoring using an underwater visual census and underwater photo transect conducted from December 2022 to April 2023. Based on these observations, the average range of coral fish abundance was 0.453 to 0.577 individuals per square meter, with the highest value at Rumah Apung station (0.577 ind/m2). The community structure included 81 reef fish species, categorized into major (50 species), indicator (10 species), and target (21 species) groups, demonstrating a community with moderate diversity, stable evenness, and low dominance across the observed stations. Further, the research quantified fish biomass, recording an average of 0.0207 kg/m2 or 207.571 kg/Ha, categorized as low, with the highest biomass measurements at Rumah Apung station (0.0054 kg/m2). Strong correlations were identified between coral cover and both fish abundance (correlation coefficient = 0.741) and biomass (correlation coefficient = 0.666). These results emphasize the profound impact of coral health on the conditions and sustainability of reef fish populations. These findings underscore the critical dependency of reef fish on coral ecosystems and provide essential data for conservation efforts to maintain and restore these vital marine habitats.

Gaidropsarus mauritanicus (Gadiformes, Gaidropsaridae) a new three-bearded rockling from a deep-water coral ecosystem with a genetically verified biogeographical distribution of the genus and notes to its ecology and behavior.

Gaidropsarus mauritanicus sp. nov. is described from one specimen collected using a grab sample from the Tanoûdêrt Canyon (ca. 20° N) off Mauritania at a depth of 595 m. The new species was further observed during eight remotely operated vehicle (ROV) dives along the Mauritanian slope southwards down to the Tiguent Coral Mound Complex (~17° N) in a bathymetric range between 613 and 416 m. It can be distinguished from congeners by a combination of characteristics, including large eyes (38.1% head length [HL]), large head (25.8% standard length [SL]), elongated pelvic fins (35.7% SL), low number of vertebrae (44), and coloration (pinkish with a dorsal darker brownish hue and bright blotches along the dorsal-fin base). A species-delimitation analysis performed with available cytochrome c oxidase subunit 1 (COI) sequences affiliated to the genus Gaidropsarus additionally supported the validity of the new species. Video analyses showed a deep-water coral-associated and protection-seeking behavior, which may explain why the species has remained undescribed until now. Additional ROV footage from separate deep-water coral sites in the North Atlantic and Mediterranean Sea further highlights the ecological behavior and hidden diversity of bathyal three-bearded rocklings. Here, we additionally discuss the biogeographical distribution of all genetically verified Gaidropsarus spp. in combination with genetic data and morphological characters. G. mauritanicus sp. nov. is closely related to a species from Tasmania (43° S), a geographical point furthest among the studied samples, which may hint to an important influence of (paleo-) oceanography on the distributions of Gaidropsarus species.

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.

Distinct diversity, assembly, and co-occurrence patterns of the prokaryotic microbiome in coral ecosystems of the South China Sea

Coral reefs are among the most energetic marine ecosystems, taking a place in ecological balance. Microbes participate in the energy exchange in coral ecosystems, which may affect coral resistance and resilience. However, there is still a lack of understanding regarding the microbial structure between corals and seawater. In this study, microbial structure and interactions in coral and seawater were studied using quantitative PCR and high-throughput sequencing. We found that the abundance and diversity of microbes in corals were higher than those in seawater. Corals, as nonfluidic ecosystems, limited the dispersal of microbes, causing broader stochasticity in the ecological shaping process, whereas ecological drift and homogeneous selection were the most important assembly mechanisms in seawater. The microbial niche width was larger in the coral group than in the seawater group, indicating strong adaptability. A group of microbes (e.g., Caldilineaceae, Burkholderiaceae, and Nitrosopumilaceae) may become microbial indicators which differentiate seawater samples (e.g., SAR11 and SAR86 clades, Cryomorphaceae), which may be due to separated habitats and nutrition. Coral microbes may participate in nitrogen-metabolism to maintain a nitrogen limited microenvironment. Nodes linked in the coral co-occurrence network showed coexisting interactions and higher complexity based on the comparison of topological values. Collectively, significant differences in microbial fractions were demonstrated observed in terms of diversity, composition, co-occurrence patterns, assembly processes and predicted functions between coral and seawater samples, showing potential microbial interactions and providing in-depth insights into the metacommunity diversity in coral reef ecosystems.