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Endosymbiotic dinoflagellates (Symbiodiniaceae) influence coral thermal tolerance at both local and regional scales. In isolation, the effects of host genetics, environment, and thermal disturbances on symbiont communities are well understood, yet their combined effects remain poorly resolved. Here, we investigate Symbiodiniaceae across 1300 km in Australia's Coral Sea Marine Park to disentangle these interactive effects. We identified Symbiodiniaceae to species‐level resolution for three coral species (Acropora cf humilis, Pocillopora verrucosa, and Pocillopora meandrina) by sequencing two genetic markers of the symbiont (ITS2 and psbAncr), paired with genotype‐by‐sequencing of the coral host (DArT‐seq). Our samples predominantly returned sequences from the genus Cladocopium, where Acropora cf humilis affiliated with C3k, Pocillopora verrucosa with C. pacificum, and Pocillopora meandrina with C. latusorum. Multivariate analyses revealed that Acropora symbionts were driven strongly by local environment and thermal disturbances. In contrast, Pocillopora symbiont communities were both partitioned 2.5‐fold more by host genetic structure than by environmental structure. Among the two Pocillopora species, the effects of environment and host genetics explained four times more variation in symbionts for P. meandrina than P. verrucosa. The concurrent bleaching event in 2020 had variable impacts on symbiont communities, consistent with patterns in P. verrucosa and A. cf humilis, but not P. meandrina. Our findings demonstrate how symbiont macroscale community structure responses to environmental gradients depend on host species and their respective population structure. Integrating host, symbiont, and environmental data will help forecast the adaptive potential of corals and their symbionts amidst a rapidly changing environment. [ABSTRACT FROM AUTHOR]

Microbial diversity has been extensively explored in reef-building corals. However, the functional roles of coral-associated microorganisms remain poorly elucidated. Here, we recover 191 bacterial and 10 archaeal metagenome-assembled genomes (MAGs) from the coral Acropora kenti (formerly A. tenuis) and adjacent seawater, to identify microbial functions and metabolic interactions within the holobiont. We show that 82 MAGs were specific to the A. kenti holobiont, including members of the Pseudomonadota, Bacteroidota, and Desulfobacterota. A. kenti-specific MAGs displayed significant differences in their genomic features and functional potential relative to seawater-specific MAGs, with a higher prevalence of genes involved in host immune system evasion, nitrogen and carbon fixation, and synthesis of five essential B-vitamins. We find a diversity of A. kenti-specific MAGs encode the biosynthesis of essential amino acids, such as tryptophan, histidine, and lysine, which cannot be de novo synthesised by the host or Symbiodiniaceae. Across a water quality gradient spanning 2° of latitude, A. kenti microbial community composition is correlated to increased temperature and dissolved inorganic nitrogen, with corresponding enrichment in molecular chaperones, nitrate reductases, and a heat-shock protein. We reveal mechanisms of A. kenti-microbiome-symbiosis on the Great Barrier Reef, highlighting the interactions underpinning the health of this keystone holobiont. This study provides insights into the functional roles of microbial symbionts within the reef-building coral Acropora kenti. The findings reveal molecular mechanisms underpinning coral health and adaptation to local environmental stressors, which may support host resilience in the face of anthropogenic climate change and pollution. [ABSTRACT FROM AUTHOR]

Nutrient acquisition through heterotrophy is critical for the health of reef-building corals. The optimization of exogenous nutrition protocols to support a diversity of aquaculture corals requires improved techniques to assess feeding rates. Here, we compared the feeding rates of three coral species (Acropora millepora, Pocillopora acuta and Galaxea fascicularis) fed Artemia salina through capture rate (indirect) and dissection (direct) approaches, with direct detection and enumeration within dissected polyps facilitated by fluorescent microbeads ingested by the Artemia. When A. millepora was provided Artemia at 3 individuals ml−1 for one hour, the calculated capture rates (0.7 ind. polyp−1 h−1) overestimated prey ingested compared to prey detected directly within polyps (0.2 ind. polyp−1 h−1), and ingestion varied significantly between genotypes. In contrast, for P. acuta, capture rate calculations (1 ind. polyp−1 h−1) underestimated prey detected within polyps (3.5 ind. polyp−1 h−1) and ingestion did not vary between genotypes. For G. fascicularis, the feeding rates were similar as calculated by both capture rates (59 ind. polyp−1 h−1) and by polyp dissections (75 ind. polyp−1 h−1). Results from this study provide valuable insights into coral feeding rates of different coral species that can improve prey enrichment and feeding strategies for nutritional supplementation of corals in captivity. [ABSTRACT FROM AUTHOR]

Despite the ecological significance of the mutualistic relationship between Symbiodiniaceae and reef‐building corals, the molecular interactions during establishment of this relationship are not well understood. This is particularly true of the transcriptional changes that occur in the symbiont. In the current study, a dual RNA‐sequencing approach was used to better understand transcriptional changes on both sides of the coral–symbiont interaction during the colonization of Acropora tenuis by a compatible Symbiodiniaceae strain (Cladocopium goreaui; ITS2 type C1). Comparison of transcript levels of the in hospite symbiont 3, 12, 48 and 72 hr after exposure to those of the same strain in culture revealed that extensive and generalized down‐regulation of symbiont gene expression occurred during the infection process. Included in this "symbiosis‐derived transcriptional repression" were a range of stress response and immune‐related genes. In contrast, a suite of symbiont genes implicated in metabolism was upregulated in the symbiotic state. The coral data support the hypothesis that immune‐suppression and arrest of phagosome maturation play important roles during the establishment of compatible symbioses, and additionally imply the involvement of some SCRiP family members in the colonization process. Consistent with previous ecological studies, the transcriptomic data suggest that active translocation of metabolites to the host may begin early in the colonization process, and thus that the mutualistic relationship can be established at the larval stage. This dual RNA‐sequencing study provides insights into the transcriptomic remodelling that occurs in C. goreaui during transition to a symbiotic lifestyle and the novel coral genes implicated in symbiosis. [ABSTRACT FROM AUTHOR]

Corals are associated with diverse microbial assemblages; however, the spatialtemporal dynamics of intra-species microbial interactions are poorly understood. The coral-associated microbial community varies substantially between tissue and mucus microhabitats; however, the factors controlling the occurrence, abundance, and distribution of microbial taxa over time have rarely been explored for different coral compartments simultaneously. Here, we test (1) differentiation in microbiome diversity and composition between coral compartments (surface mucus and tissue) of two Acropora hosts (A. tenuis and A. millepora) common along inshore reefs of the Great Barrier Reef, as well as (2) the potential linkage between shifts in individual coral microbiome families and underlying host and environmental parameters. Amplicon based 16S ribosomal RNA gene sequencing of 136 samples collected over 14 months, revealed significant differences in bacterial richness, diversity and community structure among mucus, tissue and the surrounding seawater. Seawater samples were dominated by members of the Synechococcaceae and Pelagibacteraceae bacterial families. The mucus microbiome of Acropora spp. was dominated by members of Flavobacteriaceae, Synechococcaceae and Rhodobacteraceae and the tissue was dominated by Endozoicimonaceae. Mucus microbiome in both Acropora species was primarily correlated with seawater parameters including levels of chlorophyll a, ammonium, particulate organic carbon and the sum of nitrate and nitrite. In contrast, the correlation of the tissue microbiome to the measured environmental (i.e., seawater parameters) and host health physiological factors differed between host species, suggesting host-specific modulation of the tissue-associated microbiome to intrinsic and extrinsic factors. Furthermore, the correlation between individual coral microbiome members and environmental factors provides novel insights into coral microbiome-by-environment dynamics and hence has potential implications for current reef restoration and management efforts (e.g. microbial monitoring and observatory programs). [ABSTRACT FROM AUTHOR]

Coral reefs are currently under threat as a consequence of local and global stressors, in particular, mass coral bleaching induced by climate warming. In conjunction with global cuts to carbon emissions, active restoration interventions are being investigated as an additional option to buy time while these stressors are mitigated. One intervention with the potential to improve recovery during or postbleaching involves the addition of probiotic treatments, that is the addition of microorganisms that provide benefits to the host. Fragments of the branching coral, Acropora millepora, were experimentally exposed to a bleaching event coupled with the inoculation of Symbiodiniaceae probiotics (Durusdinium trenchii and Cladocopium goreaui) to determine if these probiotic treatments could ameliorate bleaching related stress and mortality. Fragments inoculated with C. goreaui and exposed to 32°C for 6 days exhibited significantly less mortality (9.1 ± 5%) compared to corals exposed to 32°C without probiotics (66.7 ± 8%) or with D. trenchii (41.7 ± 9%). Fragments in the C. goreaui probiotic treatment also bleached less and exhibited the highest photosynthetic efficiency compared to fragments inoculated with the D. trenchii at 32°C. Internal transcribed spacer‐2 amplicon sequencing did not detect the inoculated D. trenchii and C. goreaui cells within A. millepora tissues at the end of the experiment, suggesting the corals did not reestablish symbiosis but instead used inoculated cells as a nutritional supplement, although other factors such as shuffling conditions may have had an effect. This study highlights that nutritional supplementation can possibly aid coral resilience to temperature stress, though a far more detailed understanding of the factors that influence host regulation during symbiosis establishment is required. [ABSTRACT FROM AUTHOR]

Environmental conditions influence species composition, including the microbial communities that associate with benthic organisms such as corals. In this study we identified and compared bacteria that associate with three common deep-water corals, Lophelia pertusa , Madrepora oculata and Paragorgia arborea , from a reef habitat on the mid-Norwegian shelf. The 16S rRNA gene amplicon sequencing data obtained revealed that >50% of sequences were represented by only five operational taxonomic units. Three were host-specific and unclassified below class level, belonging to Alphaproteobacteria with affiliation to members of the Rhizobiales order (L. pertusa), Flavobacteria affiliated with members of the Elisabethkingia genus (M. oculata) and Mollicutes sequences affiliated with the Mycoplasma genus (P. arborea). In addition, gammaproteobacterial sequences within the genera Sulfitobacter and Oleispira were found across all three deep-water coral taxa. Although highly abundant in the coral microbiomes, these sequences accounted for <0.1% of the surrounding bacterioplankton, supporting specific relationships. We combined this information with previous studies, undertaking a meta-data analysis of 165 widespread samples across coral hosts and habitats. Patterns in bacterial diversity indicated enrichment of distinct uncultured species in coral microbiomes that differed among deep (>200 m), mesophotic (30–200 m) and shallow (<30 m) reefs. [ABSTRACT FROM AUTHOR]

Genotype-specific contributions to the environmental tolerance and disease susceptibility of corals are widely accepted. Yet our understanding of how host genotype influences the composition and stability of the coral microbiome subjected to environmental fluctuations is limited. To gain insight into the community dynamics and environmental stability of microbiomes associated with distinct coral genotypes, we assessed the microbial community associated with Acropora tenuis under single and cumulative pressure experiments. Experimental treatments comprised either a single pulse of reduced salinity (minimum of 28 psu) or exposure to the cumulative pressures of reduced salinity (minimum of 28 psu), elevated seawater temperature (+2 C), elevated pCO2 (900 ppm), and the presence of macroalgae. Analysis of 16S rRNA gene amplicon sequence data revealed that A. tenuis microbiomes were highly host-genotype specific and maintained high compositional stability irrespective of experimental treatment. On average, 48% of the A. tenuis microbiome was dominated by Endozoicomonas. Amplicon sequence variants (ASVs) belonging to this genus were significantly different between host individuals. Although no signs of stress were evident in the coral holobiont and the vast majority of ASVs remained stable across treatments, a microbial indicator approach identified 26 ASVs belonging to Vibrionaceae, Rhodobacteraceae, Hahellaceae, Planctomycetes, Phylobacteriaceae, Flavobacteriaceae, and Cryomorphaceae that were significantly enriched in corals exposed to single and cumulative stressors. While several recent studies have highlighted the efficacy of microbial indicators as sensitive markers for environmental disturbance, the high host-genotype specificity of coral microbiomes may limit their utility and we therefore recommend meticulous control of host-genotype effects in coral microbiome research. [ABSTRACT FROM AUTHOR]

Recurrent disturbances on coral reefs that cause injuries, like predation and storm damage, and elevated seawater temperatures reduce coral fitness and immunocompetence. An effective immune response is essential to prevent disease and enhance colony survival. To evaluate how elevated seawater temperatures affect the coral immune response following injury, fragments of Acropora aspera were exposed to ambient (27-29°C) or elevated (32-33.5°C) seawater temperatures for 8 days and subsequently experimentally injured. Expression patterns for 15 immune genes 24 h post-injury revealed that most genes involved in the Toll-like receptor pathway were unaffected by elevated seawater temperatures. Exceptions to this pattern were cFos and cJun, which were upregulated and likely played a role in repair processes, and TRAF- 6 and NFκB, which were downregulated suggesting reduced immune function. Components of the complement system were upregulated ( millectin, C3) or downregulated ( Bf, Tx60, apextrin) in corals at high temperatures. However, corals that also sustained injury, showed normal Tx60 and apextrin expression, suggesting roles in the wounding response. Overall, basal expression levels of immune genes are sufficient to mount a response to injury in the short term, and the immune response of A. aspera following injury is not significantly affected by minor elevations in seawater temperatures. [ABSTRACT FROM AUTHOR]

Bacteria associated with three coral species, Acropora tenuis, Pocillopora damicornis and Tubastrea faulkneri, were assessed before and after coral mass spawning on Ningaloo Reef in Western Australia. Two colonies of each species were sampled before and after the mass spawning event and two additional samples were collected for P. damicornis after planulation. A variable 470 bp region of the 16 S rRNA gene was selected for pyrosequencing to provide an understanding of potential variations in coral-associated bacterial diversity and community structure. Bacterial diversity increased for all coral species after spawning as assessed by Chao1 diversity indicators. Minimal changes in community structure were observed at the class level and data at the taxonomical level of genus incorporated into a PCA analysis indicated that despite bacterial diversity increasing after spawning, coral-associated community structure did not shift greatly with samples grouped according to species. However, interesting changes could be detected from the dataset; for example, a-Proteobacteria increased in relative abundance after coral spawning and particularly the Roseobacter clade was found to be prominent in all coral species, indicating that this group may be important in coral reproduction. [ABSTRACT FROM AUTHOR]

Acropora white syndrome ( AWS) is characterized by rapid tissue loss revealing the white underlying skeleton and affects corals worldwide; however, reports of causal agents are conflicting. Samples were collected from healthy and diseased corals and seawater around American Samoa and bacteria associated with AWS characterized using both culture-dependent and culture-independent methods, from coral mucus and tissue slurries, respectively. Bacterial 16 S r RNA gene clone libraries derived from coral tissue were dominated by the Gammaproteobacteria, and Jaccard's distances calculated between the clone libraries showed that those from diseased corals were more similar to each other than to those from healthy corals. 16 S r RNA genes from 78 culturable coral mucus isolates also revealed a distinct partitioning of bacterial genera into healthy and diseased corals. Isolates identified as Vibrionaceae were further characterized by multilocus sequence typing, revealing that whilst several Vibrio spp. were found to be associated with AWS lesions, a recently described species, Vibrio owensii, was prevalent amongst cultured Vibrio isolates. Unaffected tissues from corals with AWS had a different microbiota than normal Acropora as found by others. Determining whether a microbial shift occurs prior to disease outbreaks will be a useful avenue of pursuit and could be helpful in detecting prodromal signs of coral disease prior to manifestation of lesions. [ABSTRACT FROM AUTHOR]

This study compared the effect of heat stress on coral-associated bacterial communities among juveniles of the coral, Acropora tenuis, hosting different Symbiodinium types. In comparison to a control temperature treatment (28 °C), we documented dramatic changes in bacterial associates on juvenile corals harbouring ITS 1 type D Symbiodinium when placed in a high (32 °C) temperature treatment. In particular, there was a marked increase in the number of retrieved Vibrio affiliated sequences, which coincided with a 44% decline in the photochemical efficiency of the D-juveniles. Interestingly, these Vibrio sequences affiliated most closely with the coral pathogen, Vibrio coralliilyticus, which has been implicated in some coral disease outbreaks. In contrast, A. tenuis hosting ITS 1 type C1 Symbiodinium did not exhibit major bacterial shifts in the elevated temperature treatment, indicating a more stable bacterial community during thermal stress; concomitantly a decline (10%) in photochemical efficiency was minimal for this group. D juveniles that had been exposed to moderately elevated sea temperatures (30 °C) in the field before being placed in the control temperature treatment displayed a decrease in the number of Vibrio affiliated sequences and bacterial profiles shifted to become more similar to profiles of corals harbouring type C1 Symbiodinium. In combination, these results demonstrate that thermal stress can result in shifts in coral-associated bacterial communities, which may lead to deteriorating coral health. The lower resilience of A. tenuis to thermal stress when harbouring Symbiodinium D highlights the importance of inter-kingdom interactions among the coral host, dinoflagellate endosymbiont and bacterial associates for coral health and resilience. [ABSTRACT FROM AUTHOR]

Rates of progression and transmission of black band disease (BBD) on the staghorn coral, Acropora muricata, were compared between months for seasonal in situ studies and between temperature treatments in experimental aquaria manipulations at Lizard Island on the Great Barrier Reef (GBR). In situ field experiments demonstrated that BBD progressed along branches approximately twice as fast (1.7–2.4 times) during the austral summer month of January (0.99 ± 0.04 cm/day) than in the cooler months of July (0.58 ± 0.04 cm/day) and May (0.41 ± 0.07 cm/day). Transmission of BBD between colonies was also accelerated in warmer months, with signs of infection becoming visible 1.2 days earlier in January compared to May. The greater seawater temperatures by ∼2 to 3°C and light intensities by up to 650 μE/m2/s in January, suggest that rates of progression and transmission of BBD are linked to one or both of these parameters. Manipulative experiments in summer provide corroborative evidence that elevated temperatures increase rates of BBD progression, with the disease progressing 1.3 times more rapidly in the 32°C elevated temperature treatment than in the 30°C ambient treatment (1.17 ± 0.06 cm/day versus 0.92 ± 0.07 cm/day; F 2,6 = 7.66, P = 0.022). In contrast, although a trend for greatest BBD progression was measured in elevated temperature treatments of 29°C (0.46 ± 0.07 cm/day) and 31°C (0.52 ± 0.06 cm/day) in winter, these rates did not differ significantly ( F 3,7 = 1.72, P = 0.249) from those measured for the ambient 27°C treatment (0.37 ± 0.06 cm/day) or the field controls (0.41 ± 0.09 cm/day). The lower rates of BBD progression in the 31°C winter treatment (0.52 ± 0.06 cm/day) than in the 30°C (0.92 ± 0.07 cm/day) summer treatment, may have been a response to 28-fold decreased light irradiance in the former, suggesting that high irradiance in combination with elevated temperatures may promote progression of BBD. Results from this study indicate that the impact of elevated temperature on BBD progression is complex with a combination of environmental factors including temperature and light playing key roles in progression and transmission of the disease. [ABSTRACT FROM AUTHOR]

Bacterial diversity associated with corals has been studied extensively, however, localization of bacterial associations within the holobiont is still poorly resolved. Here we provide novel insight into the localization of coral-associated microbial aggregates (CAMAs) within tissues of the coral Acropora hyacinthus. In total, 318 and 308 CAMAs were characterized via histological and fluorescent in situ hybridization (FISH) approaches respectively, and shown to be distributed extensively throughout coral tissues collected from five sites in Japan and Australia. The densities of CAMAs within the tissues were negatively correlated with the distance from the coastline (i.e. lowest densities at offshore sites). CAMAs were randomly distributed across the six coral tissue regions investigated. Within each CAMA, bacterial cells had similar morphological characteristics, but bacterial morphologies varied among CAMAs, with at least five distinct types identified. Identifying the location of microorganisms associated with the coral host is a prerequisite for understanding their contributions to fitness. Localization of tissue-specific communities housed within CAMAs is particularly important, as these communities are potentially important contributors to vital metabolic functions of the holobiont. [ABSTRACT FROM AUTHOR]

Background: Coral reefs can experience salinity fluctuations due to rainfall and runoff; these events can have major impacts on the corals and lead to bleaching and mortality. On the Great Barrier Reef (GBR), low salinity events, which occur during summer seasons and can involve salinity dropping ~ 10 PSU correlate with declines in coral cover, and these events are predicted to increase in frequency and severity under future climate change scenarios. In other marine invertebrates, exposure to low salinity causes increased expression of genes involved in proteolysis, responses to oxidative stress, and membrane transport, but the effects that changes in salinity have on corals have so far received only limited attention. To better understand the coral response to hypo-osmotic stress, here we investigated the transcriptomic response of the coral Acropora millepora in both adult and juvenile life stages to acute (1 h) and more prolonged (24 h) exposure to low salinity. Results: Differential gene expression analysis revealed the involvement of both common and specific response mechanisms in Acropora. The general response to environmental stressors included up-regulation of genes involved in the mitigation of macromolecular and oxidative damage, while up-regulation of genes involved in amino acid metabolism and transport represent specific responses to salinity stress. Conclusions: This study is the first comprehensive transcriptomic analysis of the coral response to low salinity stress and provides important insights into the likely consequences of heavy rainfall and runoff events on coral reefs. [ABSTRACT FROM AUTHOR]

Phylogenetic evidence is provided for horizontal transfer of a natterin-like toxin encoding gene from fungi into the genome of the coral Acropora digitifera. Sequencing analysis of the coral tissues supported that a fungal taxon predicted to be the most likely gene donor was represented in the coral microbiome. Further bioinformatics data suggested widespread recruitment of the natterin-like gene into venomous terrestrial invertebrates, and repositioning of this gene to non-toxic functions in non-venomous teleost fish. [ABSTRACT FROM AUTHOR]

A dynamic mucous layer containing numerous micro-organisms covers the surface of corals and has multiple functions including both removal of sediment and "food gathering." 1 It is likely to also act as the primary barrier to infection; various proteins and compounds with antimicrobial activity have been identified in coral mucus, though these are thought to be largely or exclusively of microbial origin. As in Hydra, 2 anti-microbial peptides (AMPs) are likely to play major roles in regulating the microbiomes of corals. 3,4 Some eukaryotes employ a complementary but less obvious approach to manipulate their associated microbiome by interfering with quorum signaling, effectively preventing bacteria from coordinating gene expression across a population. Our investigation of immunity in the reef-building coral Acropora millepora , 5 however, led to the discovery of a coral gene referred to here as AmNtNH1 that can inactivate a range of acyl homoserine lactones (AHLs), common bacterial quorum signaling molecules, and is induced on immune challenge of adult corals and expressed during the larval settlement process. Closely related proteins are widely distributed within the Scleractinia (hard corals) and some other cnidarians, with multiple paralogs in Acropora , but their closest relatives are bacterial, implying that these are products of one or more lateral gene transfer events post-dating the cnidarian-bilaterian divergence. The deployment by corals of genes used by bacteria to compete with other bacteria reflects a mechanism of microbiome manipulation previously unknown in Metazoa but that may apply more generally. • Coral immune responses include inactivation of bacterial quorum signals • Inactivation is via a coral hydrolase that can cleave acyl homoserine lactones • The Acropora hydrolase gene was acquired from a bacterium via an ancient LGT • Duplication events have led to complex repertoires of related genes in some corals Mason et al. discovered a protein encoded by Acropora corals that inactivates a range of acyl homoserine lactones, common bacterial quorum signaling molecules. Homologs are present in corals and other cnidarians, but not in other Metazoa. The gene underlying this novel defense activity has bacterial origins and was acquired via an ancient LGT. [ABSTRACT FROM AUTHOR]

High post-settlement mortality in ex situ sexually propagated coral recruits remains a significant bottleneck to production of corals for reef restoration, scientific experiments and the ornamental trade. Co-culture with grazing herbivores represents a potentially cost-effective method to reduce recruit competition with algae, thus improving the survival and yield of corals. Here we examined the effectiveness of co-culture of coral recruits of Acropora millepora, A. tenuis, A. secale, Porites lobata and Platygyra daedalea with herbivorous gastropods, Calthalotia strigata and Turbo haynesi, and herbivorous juveniles of the Asteroid Acanthaster cf. solaris. Coral recruits (200 per species) were settled onto individual aragonite plugs, with 10 plugs per species introduced to twenty 50 L experimental tanks. Each tank was randomly assigned to one of five grazing treatments; (1) Thalotia, 30 C. strigata per tank, (2) Turbo, 30 T. haynesi per tank, (3) CoTS, 30 A. cf. solaris per tank, (4) Mix, 10 C. strigata , 10 T. haynesi and 20 A. cf. solaris per tank, and (5) Control, no grazers added. We found that over a 2-month period single species co-culture with C. strigata significantly improved the survival of A. millepora, A. tenuis, A. secale and P. lobata , whilst P. daedalea benefitted most from co-culture with T. haynesi. Over 6-months, C. strigata produced the highest survival in A. millepora (51.6% ± 5.24%), A. tenuis (46.6% ± 3.16%) and A. secale (38.5% ± 3.48%), but T. haynesi co-culture resulted in higher survival in P. lobata (67.3% ± 3.76%) and P. daedalea (100% ± 0%). These results were all significantly higher than the survival of corals in controls, which after 6 months averaged ~1.87% for the Acropora species, 43.0% ± 4.79% and 57.6% ± 8.60% for P. lobata and P. daedalea respectively. Increase in basal surface area of recruits was varied, with the highest relative increases in recruit basal disk area occurring in Thalotia treatments for A. millepora and A. secale, in Turbo for A. tenuis , and in the Control tanks for P. lobata and P. daedalea. This study provides strong evidence that co-culture with C. strigata can improve ex situ sexual coral propagation, with minimal additional intervention from aquarists. The large increase (23.6× higher) in survival of ecologically and economically important coral species such as A. millepora demonstrates the potential of co-culture to enhance ex situ coral propagation. • Co-culture with gastropods resulted in 23× increase in A. millepora survival. • Gastropod co-culture could also improve growth of coral recruits. • Positive effects of co-culture were consistent across different species of corals. • Survivals with gastropods were comparable to previous survivals with sea urchins. [ABSTRACT FROM AUTHOR]

Reef restoration activities and the ornamental trade are increasing the demand for sexually propagated corals. One challenge faced in scaling up the aquaculture production of corals is high mortality as a result of fouling organisms overgrowing coral spat, with manual removal of algae and other fouling organisms being costly and time consuming. Here we test the use of microherbivore grazers as a potential biocontrol method for fouling in coral aquaculture and compare their effectiveness to manual cleaning by an aquarist. Recruits of six coral species (Acropora millepora, Acropora kenti, Goniastrea retiformis, Porites lobata, Dipsastraea speciosa and Lobophyllia corymbosa) were reared for 112 days with aquarist cleaning, or co-cultured with gastropods (Calthalotia strigata or Turbo haynesi), sea urchins (Tripneustes gratilla or Echinomentra mathaei) , the hermit crab Clibanarius cf. taeniatus or under a control treatment with no grazers. Corals grown in the aquarist cleaning treatment displayed high survival and growth, though similar responses were observed for most coral species grown with C. strigata or T. gratilla , likely due to minimal damage via overgrazing and the promotion of relatively short turf algal communities in these treatments. However, effort required, measured as average cleaning time, was 2–3 times greater in the aquarist treatment compared to C. strigata or T. gratilla treatments. Survival of coral recruits housed with C. cf. taeniatus , E. mathaei or T. haynesi were variable, likely due to the dominance of long, filamentous turf algae in tanks with E. mathaei, and physical disturbance to recruits by C. cf. taeniatus and T. haynesi. Our results demonstrate microherbivores have potential for application in aquaculture to promote production, while also reducing labour costs. • Multiple coral species showed positive responses to co-culture with microherbivores. • Survival and growth with microherbivores were comparable to aquarist cleaning. • Acroporid corals typically performed best with small gastropods. • Non-Acroporid corals performed best with juvenile sea urchin. • Husbandry effort was 3× lower in co-culture tanks compared to aquarist cleaned. [ABSTRACT FROM AUTHOR]

Marine bacteria play a central role in the degradation of dimethylsulfoniopropionate (DMSP) to dimethyl sulfide (DMS) and acrylic acid, DMS being critical to cloud formation and thereby cooling effects on the climate. High concentrations of DMSP and DMS have been reported in scleractinian coral tissues although, to date, there have been no investigations into the influence of these organic sulfur compounds on coral-associated bacteria. Two coral species, Montipora aequituberculata and Acropora millepora, were sampled and their bacterial communities were characterized by both culture-dependent and molecular techniques. Four genera, Roseobacter, Spongiobacter, Vibrio, and Alteromonas, which were isolated on media with either DMSP or DMS as the sole carbon source, comprised the majority of clones retrieved from coral mucus and tissue 16S rRNA gene clone libraries. Clones affiliated with Roseobacter sp. constituted 28% of the M. aequituberculata tissue libraries, while 59% of the clones from the A. millepora libraries were affiliated with sequences related to the Spongiobacter genus. Vibrio spp. were commonly isolated from DMS and acrylic acid enrichments and were also present in 16S rRNA gene libraries from coral mucus, suggesting that under "normal" environmental conditions, they are a natural component of coral-associated communities. Genes homologous to dddD, and dddL, previously implicated in DMSP degradation, were also characterized from isolated strains, confirming that bacteria associated with corals have the potential to metabolize this sulfur compound when present in coral tissues. Our results demonstrate that DMSP, DMS, and acrylic acid potentially act as nutrient sources for coral-associated bacteria and that these sulfur compounds are likely to play a role in structuring bacterial communities in corals, with important consequences for the health of both corals and coral reef ecosystems. [ABSTRACT FROM AUTHOR]

Pest management is a critical component of aquaculture operations since high stocking densities can facilitate rapid pest infestation and high stock losses. The Acropora eating-flatworm, Prosthiostomum acroporae impact the health of captive Acropora colonies, which are commonly grown as part of coral aquaculture for trade, research and the hobbyist sector. We investigated the efficacy of anthelmintics levamisole and praziquantel for the removal of Acropora -eating flatworms from A. millepora using one-hour chemical immersions and assessed if these treatments negatively impacted coral growth and/or caused bleaching. Coral fragments (194 total) were spread across eight treatments; levamisole infested (LI; n = 20), levamisole uninfested (LU; n = 20), praziquantel (in EtOH) infested (PI; n = 20), praziquantel (in EtOH) uninfested (PU; n = 20), handling control infested (HCI; n = 14), handling control uninfested (HCU; n = 20), EtOH control (EC; n = 40), control with no handling (NHC; n = 40). To test the efficacy of flatworm removal by short, one-hour chemical immersions, A. millepora fragments (54 total) were manually infested (three P. acroporae per fragment) and immersed separately to uninfested A. millepora fragments (60 total). All fragments were shaken in in a bath of seawater following immersion, then mechanically screened to recover any flatworms not removed from either immersion or shaking to determine the removal efficacy of the treatments. Furthermore, coral fragments (194 total) were photographed before treatment and four weeks following treatments to compare coral basal growth and visual signs of bleaching between infested and uninfested fragments. Levamisole and praziquantel immersions removed significantly more flatworms from A. millepora fragments (93% ± 3.8 and 95.0% ± 2.6 respectively; mean ± SE; p < 0.05) compared to the handling control (26% ± 7.5%). Chemical treatments had no significant effect on basal growth, with fragments across all treatments (including controls) increasing basal area by 73.31 ± 3.82% (mean ± SE). Furthermore, bleaching was not observed for any A. millepora fragments across the treatments and controls. Results from this study demonstrate that levamisole and praziquantel used in conjunction with water movement were effective at removing >90% of Acropora eating-flatworms with no observable negative impacts on coral health on treated coral fragments relative to controls. • Evaluated the use of chemical treatment for Prosthiostomum acroporae infestations in coral aquaculture • Levamisole and praziquantel successfully removed flatworms from infested Acropora millepora fragments • Chemical treatments did not compromise coral basal growth or cause detectable bleaching • Developed pest management tools for P. acroporae in coral aquaculture [ABSTRACT FROM AUTHOR]