Anatomy of coral polyp. Basal body wall not shown. Inset (A), shows close up of mucus layer, epidermis and upper gastrodermis. Inset (B), shows close up of coral gastrovascular cavity.

Anatomy of coral polyp. Basal body wall not shown. Inset (A), shows close up of mucus layer, epidermis and upper gastrodermis. Inset (B), shows close up of coral gastrovascular cavity.

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In the last two decades, genetic and genomic studies have revealed the astonishing diversity and ubiquity of microorganisms. Emergence and expansion of the human microbiome project has reshaped our thinking about how microbes control host health—not only as pathogens, but also as symbionts. In coral reef environments, scientists have begun to exami...

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... The endosymbiotic relationship between the coral host and photosynthetic dinoflagellates (family Symbiodiniaceae) provides up to 90% of the host nutritional demands, and it is critical to sustaining reef ecosystem functioning [3,4]. In addition to Symbiodiniaceae, other microorganisms, notably prokaryotes (referred to as the microbiome hereafter), associate with corals and play an important role in coral physiology and health [5][6][7][8][9][10]. The coral microbiome is involved, among other chemical and biological processes, in carbon, nitrogen, and sulfur cycling, defense against pathogens, environmental adaptability, and degradation of toxic compounds [9][10][11][12][13][14][15][16][17]. ...
... In addition to Symbiodiniaceae, other microorganisms, notably prokaryotes (referred to as the microbiome hereafter), associate with corals and play an important role in coral physiology and health [5][6][7][8][9][10]. The coral microbiome is involved, among other chemical and biological processes, in carbon, nitrogen, and sulfur cycling, defense against pathogens, environmental adaptability, and degradation of toxic compounds [9][10][11][12][13][14][15][16][17]. However, the elaborated interactions between the host and its microbiome are complex, and it is yet to be fully understood how microbial communities can improve coral holobiont functions to tolerate environmental stressors, particularly those derived from ocean warming [9,13]. ...
... Despite the increasing number of microbiome studies in recent years, e.g., [10,35], the number of publications on the Red Sea remains relatively small in comparison to other regions, such as the Great Barrier Reef, and has focused only on a few coral species and/or has been restricted to certain regions [27]. Few studies have assessed the coral microbiome composition and its dynamics along its latitudinal gradient in the Red Sea, e.g., [21,36,37]. ...
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The Red Sea is a suitable model for studying coral reefs under climate change due to its strong environmental gradient that provides a window into future global warming scenarios. For instance, corals in the southern Red Sea thrive at temperatures predicted to occur at the end of the century in other biogeographic regions. Corals in the Red Sea thrive under contrasting thermal and environmental regimes along their latitudinal gradient. Because microbial communities associated with corals contribute to host physiology, we conducted a systematic review of the known diversity of Red Sea coral-associated bacteria, considering geographic location and host species. Our assessment comprises 54 studies of 67 coral host species employing cultivation-dependent and cultivation-independent techniques. Most studies have been conducted in the central and northern Red Sea, while the southern and western regions remain largely unexplored. Our data also show that, despite the high diversity of corals in the Red Sea, the most studied corals were Pocillopora verrucosa, Dipsastraea spp., Pleuractis granulosa, and Stylophora pistillata. Microbial diversity was dominated by bacteria from the class Gammaproteobacteria, while the most frequently occurring bacterial families included Rhodobacteraceae and Vibrionaceae. We also identified bacterial families exclusively associated with each of the studied coral orders: Scleractinia (n = 125), Alcyonacea (n = 7), and Capitata (n = 2). This review encompasses 20 years of research in the Red Sea, providing a baseline compendium for coral-associated bacterial diversity.
... Environmental changes such as rising sea surface temperatures (Hoegh-Guldberg et al., 2007;Hughes et al., 2017), ocean acidification (Hoegh-Guldberg et al., 2007), and pollution (Silbiger et al., 2018) have resulted in substantial degradation to coral reefs worldwide. As reefs worldwide change in both structure and function (McFall-Ngai et al., 2013;Thompson et al., 2015;Ainsworth and Gates 2016;Apprill, 2017;Trevathan-Tackett et al., 2019), it is increasingly important to understand the contribution of the microbiome to the health, physiology, and environmental flexibility of coral species. Most studies investigating the coral microbiome have predominately focused on profiling microbial communities via next generation sequencing of 16S rRNA gene amplicons using whole fragments of individual corals, such as sections of branches collected from the colony of a branching coral species. ...
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As sequencing techniques have advanced and become cheaper in recent years, there has been a rapid increase in the number of studies conducted into the role of the microbiome in coral health, physiology, and response to environmental change. However, there is substantial variation in the methodological approaches applied. For example, DNA extraction protocols and the types of tissues sampled from the coral meta-organism are known to influence the downstream analyses of the amplified microbial communities and subsequently the interpretation of the microbiome diversity, stability and role. Studies have generally focused on whole organisms, in which the coral sampling steps homogenize the meta-organism microhabitats, however other studies targeting specific microhabitats have identified sources of variation specific to distinct compartments of the coral’s microbial landscape. Here we present a comparative analysis of methodologies optimized for the generation of coral microbiome data from the coral tissues and whole coral fragments of two commonly studied branching coral genera with distinct tissue structure. We investigate the microbiome of the imperforate Pocillopora, where the coral tissue does not penetrate through the calcium carbonate matrix, and the perforate Acropora, where the coral tissues and skeleton are interwoven throughout the coral branch. Through comparing data generated from different DNA extraction protocols using fixed coral tissues isolated from the coral skeletal structure with fixed whole coral fragments, we identify sources of variation inherent to microbial data generated from different sample types, species, and extraction protocols.
... Thus, coral-symbiotic bacteria are considered as an effective sign of coral fitness (Thompson et al., 2015;Zhu et al., 2021) as they play substantial function in sustaining the healthiness of coral reef networks, biogeochemical cycles and nutrient transformation (Yu et al., 2021). Many bacterial groups can assist coral acclimatize to rise in sea surface temperature (SST) (Osman et al., 2020), eutrophication, and turbidness (Ziegler et al., 2017). ...
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Coral–bacterial interaction is a major driver in coral acclimatization to the stressful environment. 16S rRNA High‐throughput sequencing was used to classify the role of different coral reef compartments; sediment, water, and tissue; in the South China Sea (SCS), as well as different locations in shaping the microbial community. The majority of OTUs significantly shifted at impacted sites and indicated distinction in the relative abundance of bacteria compartment/site‐wise. Richness and diversity were higher, and more taxa were enriched in the sediment communities. Proteobacteria dominated sediment samples, while Cyanobacteria dominated water samples. Coral tissue showed a shift among different sites with Proteobacteria remaining the dominant Phylum. Moreover, we report a dominance of Chlorobium genus in the healthy coral tissue sample collected from the severely damaged Site B, suggesting a contribution to tolerance and adaptation to the disturbing environment. Thus, revealing the complex functionally diverse microbial patterns associated with biotic and abiotic disturbed coral reefs will deliver understanding of the symbiotic connections and competitive benefit inside the hosts niche and can reveal a measurable footprint of the environmental impacts on coral ecosystems. We hence, urge scientists to draw more attention towards using coral microbiome as a self‐sustaining tool in coral restoration.
... Microbes play critical roles in coral health-providing nutrients to the coral host and producing antibiotics, that may protect the host against harmful bacteria (Ritchie 2006;Krediet et al. 2013; Thompson et al. 2015). Corals regulate their microbiome through production of a physical and chemical mucus barrier, direct consumption of bacteria, recognition and removal of pathogens by phagocytosis or encapsulation, production of antimicrobial peptides and pore-forming proteins, and via hosting predatory bacteria and bacteriophage that may selectively prey on pathogenic bacteria (Palmer and Traylor-Knowles 2012;Krediet et al. 2013; Thompson et al. 2015;Welsh et al. 2015;Mydlarz et al. 2016;Walters et al. 2020). ...
... Microbes play critical roles in coral health-providing nutrients to the coral host and producing antibiotics, that may protect the host against harmful bacteria (Ritchie 2006;Krediet et al. 2013; Thompson et al. 2015). Corals regulate their microbiome through production of a physical and chemical mucus barrier, direct consumption of bacteria, recognition and removal of pathogens by phagocytosis or encapsulation, production of antimicrobial peptides and pore-forming proteins, and via hosting predatory bacteria and bacteriophage that may selectively prey on pathogenic bacteria (Palmer and Traylor-Knowles 2012;Krediet et al. 2013; Thompson et al. 2015;Welsh et al. 2015;Mydlarz et al. 2016;Walters et al. 2020). However, warming-induced stress may alter these processes, resulting in loss of beneficial bacterial associates or gain of pathogenic microbes that could compromise coral health (Ritchie 2006;Zaneveld et al. 2016). ...
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Coral reefs are undergoing precipitous decline due to coral bleaching and disease following warming events, with impacted reefs often shifting from coral to macroalgal dominance. We reciprocally transplanted three common coral species between two pairs of coral-dominated marine-protected areas (MPAs) and adjacent macroalgal-dominated fished areas to test for the effects of reef origin and transplant area on coral defense against the common coral pathogen Vibrio coralliilyticus. For the ecologically sensitive species Acropora millepora, both reef origin and transplant area influenced the potency of defense, but for the ecologically hardy coral Porites cylindrica or the weedy coral Pocillopora damicornis, potency was not altered. A. millepora colonies that originated from, or were transplanted into, coral-dominated MPAs exhibited a 46% and 38% increase, respectively, in inhibition of V. coralliilyticus relative to those that originated from, or were transplanted into, macroalgal-dominated fished areas. A. millepora also exhibited reef origin effects on its microbial community composition, notably with persistently higher relative abundances of Vibrionaceae among individuals that originated from macroalgal-dominated fished areas compared to individuals that originated from coral-dominated MPAs. For ecologically important but disease and bleaching susceptible species like acroporids, macroalgal-dominated reefs may suppress coral defense against Vibrio pathogens and facilitate blooms of Vibrio bacteria that may harm corals during periods of thermal stress. However, their defense against Vibrio coralliilyticus recovered when not subjected to degraded reefs dominated by macroalgae.
... Promising environment-friendly antifouling compounds are expected from soft corals due to its ability to resist biofouling through chemical defense and other strategies (Tian et al., 2020). Further, chemical defense properties of the bacterial metabolites are very significant in protecting the corals from diseases and biofouling (Thompson et al., 2015;Remple et al., 2021). ...
Article
Endophytic marine bacteria are a significant unexplored resource for the search of new compounds with antifouling activity. In this study, endophytic marine bacteria isolated from Red Sea soft corals were subjected to secondary metabolites extraction and evaluation of the extracts for the antibiofilm activity to reveal compounds that can prevent biofilm bacterial colonization on surfaces. Six bacteria were isolated from two species of soft corals: Sarcophyton glaucum and Heteroxenia fuscescens. Extracts obtained from each strain were screened for antibiofilm activity against three biofilm-forming bacteria and evaluated to detect compounds with antibiofilm properties by Gas chromatography-mass spectrometry (GC-MS). The isolated strains are closely related and belong to the family Bacillaceae and all except one belong to the Bacillus genus. The extracts from the endophytes show significant antibacterial activity against the tested organisms. Biofilm formation inhibition activity of the extracts ranges from 3.16 to 98.41%. The extracts also showed significant activity against biofilm formation across all the tested strains. Compounds detected in the extracts include known compounds with antibiofilm properties such as 2,4-dimethyl-2-nitro-, 2,4-bis(1,1-dimethylethyl)-phenol, Pyrrolo[1,2-a] pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl)-; Bis(tridecyl) phthalate, Heinecosane, Pentane, and Undecane.This indicates the ability of the bacteria to produce compounds relevant in preventing biofilm colonization on surfaces which could serve as a novel source of antifouling compounds.
... In addition to living in soil, sediment or water, microbes can also associate with multicellular host organisms. These microbial communities can form stable, host-specific communities, which influence host fitness and perform crucial functions (Thompson et al., 2015). ...
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Abstract Understanding the maintenance and origin of beta diversity is a central topic in ecology. However, the factors that drive diversity patterns and underlying processes remain unclear, particularly for host‐prokaryotic associations. Here, beta diversity patterns were studied in five prokaryotic biotopes, namely, two high microbial abundance (HMA) sponge taxa (Xestospongia spp. and Hyrtios erectus), one low microbial abundance (LMA) sponge taxon (Stylissa carteri), sediment and seawater sampled across thousands of kilometers. Using multiple regression on distance matrices (MRM), spatial (geographic distance) and environmental (sea surface temperature and chlorophyll a concentrations) variables proved significant predictors of beta diversity in all five biotopes and together explained from 54% to 82% of variation in dissimilarity of both HMA species, 27% to 43% of variation in sediment and seawater, but only 20% of variation of the LMA S. carteri. Variance partitioning was subsequently used to partition the variation into purely spatial, purely environmental and spatially‐structured environmental components. The amount of variation in dissimilarity explained by the purely spatial component was lowest for S. carteri at 11% and highest for H. erectus at 55%. The purely environmental component, in turn, only explained from 0.15 to 2.83% of variation in all biotopes. In addition to spatial and environmental variables, a matrix of genetic differences between pairs of sponge individuals also proved a significant predictor of variation in prokaryotic composition of the Xestospongia species complex. We discuss the implications of these results for the HMA‐LMA dichotomy and compare the MRM results with results obtained using constrained ordination and zeta diversity.
... Other finer-scale differences observed in bacterial communities between bio-polymers could be explained by the likely dominance of bacterial taxa associated with specific eukaryotic biofoulers. Marine invertebrates are holobionts: a functional ecological unit associating the host and its various microbial communities, providing host-beneficial functions (Hoffmann et al., 2009;Thompson et al., 2015). For example, numerous studies identified Proteobacteria and Bacteroidetes as dominant phyla associated with the ascidian microbiome (Erwin et al., 2013;Dror et al., 2019), cnidarians (Brown et al., 2017), and crustaceans (Datta et al., 2018). ...
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Impacts of Marine Plastic Debris (MPD) on marine ecosystems are among the most critical environmental concerns of the past three decades. Virgin plastic is often cheaper to manufacture than recycled plastics, increasing rates of plastic released into the environment and thereby impacting ecosystem health and functioning. Along with other environmental effects, MPD can serve as a vector for marine hitchhikers, facilitating unwanted organisms' transport and subsequent spread. Consequently, there is a growing demand for more eco-friendly replacements of conventional plastic polymers, ideally with fit-for-purpose properties and a well-understood life cycle. We enriched polybutylene succinate (PBS) with three different concentrations of oyster shell to investigate the dynamics of biofouling formation over 18 weeks at the Nelson Marina, Aotearoa/New Zealand. Our study focused on oyster shell concentration as a determinant of fouling assemblages over time. While generally considered as a waste in the aquaculture sector, we used oyster shells as a variable of interest to investigate their potential for both, environmental and economic benefits. Using bacterial 16S and eukaryotic 18S rRNA gene metabarcoding, our results revealed that following immersion in seawater, time played a more critical role than substrate type in driving biofouling community structures over the study period. In total, 33 putative non-indigenous species (NIS) and 41 bacterial families with putative plastic-degrading capability were detected on the different substrates. Our analysis of NIS recruitment revealed a lower contribution of NIS on shell-enriched substrates than unadulterated polymers samples. In contrast, the different concentrations of oyster shells did not affect the specific recruitment of bacterial degraders. Taken together, our results suggest that bio-based polymers and composites with increased potential for biodegradability, recyclability, and aptitude for the selective recruitment of marine invertebrates might offer a sustainable alternative to conventional polymers, assisting to mitigate the numerous impacts associated with MPD.
... In addition to the symbiosis established with endosymbiotic dinoflagellates, corals are associated with prokaryotic symbionts. In fact, the coral host, and their microbiome (microalgal and prokaryotic symbionts) show a tightly intertwined metabolic activity (Thompson et al., 2015). Coral-associated prokaryotic microbes are taxonomically and functionally diverse and are key for maintaining the health of the holobiont (Hernandez-Agreda et al., 2018;Krediet et al., 2013;Olson et al., 2009). ...
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The globally widespread adoption of Artificial Light at Night (ALAN) began in the mid‐20th century. Yet, it is only in the last decade that a renewed research focus has emerged into its impacts on ecological and biological processes in the marine environment that are guided by natural intensities, moon phase, natural light and dark cycles and daily light spectra alterations. The field has diversified rapidly from one restricted to impacts on a handful of vertebrates, to one in which impacts have been quantified across a broad array of marine and coastal habitats and species. Here we review the current understanding of ALAN impacts in diverse marine ecosystems. The review presents the current state of knowledge across key marine and coastal ecosystems (sandy and rocky shores, coral reefs and pelagic) and taxa (birds and sea turtles), introducing how ALAN can mask seabirds and sea turtles navigation, cause changes in animals predation patterns and failure of coral spawning synchronization, as well as inhibition of zooplankton Diel Vertical Migration. Mitigation measures are recommended, however, while strategies for mitigation were easily identified, barriers to implementation are poorly understood. Finally, we point out knowledge gaps that if addressed would aid in the prediction and mitigation of ALAN impacts in the marine realm.
... Understanding how microbial biodiversity interacts with their hosts' physiology is essential for understanding animal ecology and evolution [1]. Microbial communities often influence their hosts' physiology to cope with environmental variation across habitats [2]. ...
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Metazoans host complex communities of microorganisms that include dinoflagellates, fungi, bacteria, archaea and viruses. Interactions among members of these complex assemblages allow hosts to adjust their physiology and metabolism to cope with environmental variation and occupy different habitats. Here, using reciprocal transplantation across depths, we studied adaptive divergence in the corals Orbicella annularis and O. franksi , two young species with contrasting vertical distribution in the Caribbean. When transplanted from deep to shallow, O. franksi experienced fast photoacclimation and low mortality, and maintained a consistent bacterial community. By contrast, O. annularis experienced high mortality and limited photoacclimation when transplanted from shallow to deep. The photophysiological collapse of O. annularis in the deep environment was associated with an increased microbiome variability and reduction of some bacterial taxa. Differences in the symbiotic algal community were more pronounced between coral species than between depths. Our study suggests that these sibling species are adapted to distinctive light environments partially driven by the algae photoacclimation capacity and the microbiome robustness, highlighting the importance of niche specialization in symbiotic corals for the maintenance of species diversity. Our findings have implications for the management of these threatened Caribbean corals and the effectiveness of coral reef restoration efforts.
... Nutrient enrichment alters the coral microbiome primarily through increases in opportunistic species that may contribute to disease (Thompson et al. 2015, Zaneveld et al. 2016, Shaver et al. 2017, Wang et al. 2018. While nutrient enrichment alone does not often induce mortality, the interaction of enrichment with other stressors such as thermal stress and loss of herbivorous fish species has been demonstrated to prolong bleaching and increase coral mortality (Zaneveld et al. 2016, Wang et al. 2018. ...
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Nutrient pollution is linked to coral disease susceptibility and severity, but the mechanism behind this effect remains underexplored. A recently-identified bacterial species, ‘Ca. Aquarickettsia rohweri,’ is hypothesized to parasitize the Caribbean staghorn coral, Acropora cervicornis, leading to reduced coral growth and increased disease susceptibility. Aquarickettsia rohweri is hypothesized to assimilate host metabolites and ATP and was previously demonstrated to be highly nutrient-responsive. As nutrient enrichment is a pervasive issue in the Caribbean, this study examined the effects of common nutrient pollutants (nitrate, ammonium, and phosphate) on a disease-susceptible genotype of Acropora cervicornis. Microbial diversity was found to decline over the course of the experiment in phosphate-, nitrate-, and combined-treated samples, and quantitative PCR indicated that Aquarickettsia abundance increased significantly across all treatments. Only treatments amended with phosphate, however, exhibited a significant shift in Aquarickettsia abundance relative to other taxa. Furthermore, corals exposed to phosphate had significantly lower linear extension than untreated or nitrate-treated corals after 3 weeks of nutrient exposure. Together these data suggest that while experimental tank conditions, with an elevated nutrient regime associated with coastal waters, increased total bacterial abundance, only the addition of phosphate significantly altered the ratios of Aquarickettsia compared to other members of the microbiome.