Acropora Millepora Research Articles

Symbioses are restructured by repeated mass coral bleaching

Survival of symbiotic reef-building corals under global warming requires rapid acclimation or adaptation. The impact of accumulated heat stress was compared across 1643 symbiont communities before and after the 2016 mass bleaching in three coral species and free-living in the environment across ~900kilometers of the Great Barrier Reef. Resilient reefs (less aerial bleaching than predicted from high satellite sea temperatures) showed low variation in symbioses. Before 2016, heat-tolerant environmental symbionts were common in ~98% of samples and moderately abundant (9 to 40% in samples). In corals, heat-tolerant symbionts were at low abundances (0 to 7.3%) but only in a minority (13 to 27%) of colonies. Following bleaching, environmental diversity doubled (including heat-tolerant symbionts) and increased in one coral species. Communities were dynamic (Acropora millepora) and conserved (Acropora hyacinthus and Acropora tenuis), including symbiont community turnover and redistribution. Symbiotic restructuring after bleaching occurs but is a taxon-specific ecological opportunity.

Applying behavioral studies to the ecotoxicology of corals: A case study on Acropora millepora

Behavioral responses are considered sensitive and effective indicators of organism stress. As the demand for standardized coral toxicity tests grows, innovative tools that allow for automatic and quantitative measurements of these behaviors may complement ecotoxicological studies. The rapid growth of competitive marine algae in aquaculture systems is a major issue for generating coral spat for reef restoration, and the application of non-toxic antifouling (AF) coatings might effectively mitigate this issue. While these coatings do not appear to be toxic to sensitive coral larvae, their potential to affect larval mobility has not been tested. In this context, we tested the effect of three recently-developed and potentially non-toxic AF coatings: (i) antiadhesive, (ii) cerium dioxide (CeO2-x) nanoparticle, and (iii) encapsulated biocide dichlorooctylisothiazolinone (DCOIT) on the swimming velocity and activity of Acropora millepora coral larvae for potential use in reef-restoration activities. The behavior of 32 coral larvae per AF treatment were recorded, each for 25 min, in a self-constructed dark box with two camera recording sets in parallel. The tracking analysis was performed with the software Noldus EthoVision XT. The mean larval swimming velocity on control tiles of 93.1 ± 5.6 mm min-1 (and activity of 62.8 ± 5.2%) was nearly 2-fold faster (higher) than on the antiadhesive, (CeO2-x) nanoparticle and DCOIT coatings, respectively. Larvae exposed to the DCOIT-coated tiles remained almost stationary. Although the underlying cause and consequence of these results require further investigation, tracking of coral larval swimming behavior was identified as a reliable and feasible method for assessing potential non-lethal responses to AF coatings. As changes in behavior could have significant consequences for larval survival and settlement, they are important endpoints to consider, and the quantification of behavioral responses may be a meaningful and sensitive tool. Therefore, we recommend the use of behavioral studies for coral larval assessments in ecotoxicology as a valuable endpoint. For methodological standardization and implementation, our study also features a detailed guide for video-processing and track analysis of A. millepora coral larvae in EthoVision.

Cellular adaptations leading to coral fragment attachment on artificial substrates in Acropora millepora (Am-CAM)

Reproductive propagation by asexual fragmentation in the reef-building coral Acropora millepora depends on (1) successful attachment to the reef substrate through modification of soft tissues and (2) a permanent bond with skeletal encrustation. Despite decades of research examining asexual propagation in corals, the initial response, cellular reorganisation, and development leading to fragment substrate attachment via a newly formed skeleton has not been documented in its entirety. Here, we establish the first "coral attachment model" for this species ("Am-CAM") by developing novel methods that allow correlation of fluorescence and electron microscopy image data with in vivo microscopic time-lapse imagery. This multi-scale imaging approach identified three distinct phases involved in asexual propagation: (1) the contact response of the coral fragment when contact with the substrate, followed by (2) fragment stabilisation through anchoring by the soft tissue, and (3) formation of a "lappet-like appendage" structure leading to substrate bonding of the tissue for encrustation through the onset of skeletal calcification. In developing Am-CAM, we provide new biological insights that can enable reef researchers, managers and coral restoration practitioners to begin evaluating attachment effectiveness, which is needed to optimise species-substrate compatibility and achieve effective outplanting.

Enhancing Coral Settlement Through a Novel Larval Feeding Protocol

Intensifying anthropogenic stressors have contributed to declines in reef-building corals in many regions. These disturbances result in reduced live coral cover, impacting key population-level processes such as coral larval settlement and recruitment that are essential for reef recovery. Reef restoration efforts that rely on enhanced larval supply provide a pathway for the recovery of degraded reefs. However, corals at very early life stages experience high post-settlement mortality bottlenecks, which impede stock-recruitment processes. Overcoming these bottlenecks is a high priority goal in coral restoration. Some coral larvae are known to be capable of gaining exogenous nutrients. Therefore, we hypothesised that the capacity to access exogenous nutrients may confer advantages to larval survival, settlement and post-settlement success. The present study aimed to quantify the effect of larval feeding on coral larvae settlement and early post-settlement survival. We completed an ex-situ experiment using aposymbiotic larvae of two broadcast spawning reef-building coral species - Acropora tenuis and Acropora millepora. Larvae were randomly assigned to either fed or unfed treatment groups for each species. Fed larvae received homogenised Artemia once a day, for three days. Results show that for both species, feeding significantly increased larval settlement. Feeding A. millepora larvae more than doubled mean settlement (13.0 ± 1.17 SE vs 31.4 ± 2.88 SE; p <0.001). Similarly, feeding A. tenuis larvae increased mean settlement from 18.2 ( ± 1.85 SE) to 29.9 ( ± 2.22 SE; p <0.001). Larval feeding had an immediate positive effect on spat survival, such that A. millepora and A. tenuis spat from fed treatments had increased survival three days post-settlement (89.5% ± 3.75 SE vs 70.6% ± 2.59 SE, p <0.001; 88.8% ± 2.21 SE vs 71.4% ± 3.80 SE, p <0.001, respectively). Therefore, enhancing settlement and early post-settlement survival by feeding larvae homogenised Artemia has the potential to improve the effectiveness of larval rearing protocols and coral restoration efforts.

Changes in microbial community composition affect bioactivities of mucus isolated from coral acropora millepora

Antibiotic resistance is increasingly popular together with emerging diseases presents an urgent requirement for more and more discovery of novel marine bioactive compounds. Paired-end reads of 16S rRNA sequence of bacteria living in the coral Acropora millepora obtained by the Illumina next-generation sequencing technology to be processed by DADA2 pipeline, phyloseq and ggplot2 packages showed that bleached coral mucus had an alpha diversity to be higher than healthy coral mucus. The coral surface mucus layer (SML) of healthy coral exhibited higher growth inhibition activity to Vibrio parahaemolyticus test strain than that of bleached coral in any amount (10 – 30 µL). The cytotoxicity against the colon cancer cell line HCT 116 was also clearly observed when treated with healthy SML and was 1.5 times higher than mucus was taken from bleached coral. The composition of the microbial community was shifted when corals changed from a healthy state to a bleached one, resulting in the reduction of antibacterial activity and cytotoxicity.

Growth Response of Reef-Building Corals to Ocean Acidification Is Mediated by Interplay of Taxon-Specific Physiological Parameters

Ocean acidification (OA) poses a major threat to calcifying organisms such as reef-building corals, typically leading to reduced calcification rates. Mechanisms to compensate the effects of OA on coral growth may, however, involve processes other than calcification. Yet, the physiological patterns mediating coral growth under OA are not fully understood, despite an extensive body of literature characterizing physiological changes in corals under OA. Therefore, we conducted a three-month laboratory experiment with six scleractinian coral species (Acropora humilis, Acropora millepora, Pocillopora damicornis, Pocillopora verrucosa, Porites cylindrica, and Porites lutea) to assess physiological parameters that potentially characterize growth (calcification, volume, and surface area), maintenance (tissue biomass, and lipid and protein content), and cellular stress (apoptotic activity) response under ambient (pH 7.9) and low pH (pH 7.7). We identified genus- and species-specific physiological parameters potentially mediating the observed growth responses to low pH. We found no significant changes in calcification but species showed decreasing growth in volume and surface area, which occurred alongside changes in maintenance and cellular stress parameters that differed between genera and species. Acropora spp. showed elevated cellular stress and Pocillopora spp. showed changes in maintenance-associated parameters, while both genera largely maintained growth under low pH. Conversely, Porites spp. experienced the largest decreases in volume growth but showed no major changes in parameters related to maintenance or cellular stress. Our findings indicate that growth- and calcification-related responses alone may not fully reflect coral susceptibility to OA. They may also contribute to a better understanding of the complex physiological processes leading to differential growth changes of reef-building corals in response to low pH conditions.

Interspecific differences in the response of coral trophic status to the decrease in symbiotic zooxanthellae in summer

Coral bleaching events are increasing in frequency and severity worldwide. From the perspective of energy supply, a decrease in symbiotic zooxanthellae density (ZD) during bleaching leads to a reduction in the amount of energy provided by photosynthesis to the coral host. However, there are still many unknowns about how corals maintain the stability of their energy supply when zooxanthellae decrease. In this study, 89 coral samples, including the relatively stress-tolerant massive Favia palauensis and Porites lutea and the relatively vulnerable branching Acropora millepora and Pocillopora damicornis, were collected from the Xisha Islands in the South China Sea in spring and summer 2020. The physiological parameters ZD, chl a, tissue biomass and lipid content were measured. The δ13C compositions of zooxanthellae and hosts were analyzed to explore the changes in trophic status in summer. Results show that the ZDs of A. millepora, P. damicornis, F. palauensis and P. lutea significantly decreased by 32, 29, 22 and 22%, respectively, in summer. P. lutea and F. palauensis maintained metabolic energy requirements depending largely on heterotrophy. A. millepora and P. damicornis were more dependent on consuming their own lipids. Our study shows that there are intergeneric differences in the energy maintenance mechanisms used to cope with decreases in ZD. We suggest that the higher heterotrophic ability of F. palauensis and P. lutea renders their trophic status more plastic than that of A. millepora and P. damicornis. This characteristic may potentially affect their bleaching resilience.

Effects of climate change and light limitation on coral recruits

Climate change impacts and light attenuation from suspended sediments, due to runoff, natural resuspension or dredging, can both impede the replenishment of coral populations. Here we tested the independent and combined impacts of climate change (current temperature and dissolved CO2, and 2 future climate scenarios) and a 1 mo long light attenuation period at 5 different light levels (0.1 to 4 mol photons m-2 d-1) on early Acropora millepora recruits. Additionally, we evaluated whether the effects were age dependent by comparing responses of recruits that were 1 mo old (‘early attenuation’) vs. 2 mo old (‘late attenuation’). Recruit survival, size and Symbiodiniaceae densities increased slightly under moderate future climate conditions (current temperature +0.44°C, 692 ppm pCO2), but decreased under a more severe climate scenario (+0.94°C, 985 ppm pCO2). Light attenuation significantly decreased recruit survival, size and Symbiodiniaceae densities only for recruits exposed to the late attenuation, suggesting an increasing reliance on photosynthesis as recruits age. Under the more severe climate scenario tested, recruit survival was diminished by both climate change (≤18 ± 4% [SE] in the early attenuation) and light limitation (≤32 ± 6% in the late attenuation) compared with controls. However, there was no interaction between future climate scenarios and light attenuation, indicating that these effects were additive. This study demonstrates the potential effects of light limitation and future climate conditions on coral recruitment success and highlights the need to manage the timing of sediment-generating activities near reefs to optimise light availability for several months post settlement.

Two divergent haplogroups of a sacsin-like gene in Acropora corals

Reef-building corals are declining due to environmental changes. Sacsin is a member of the heat shock proteins and has been reported as a candidate protein associated with the stress response in Acropora corals. Recently, high nucleotide diversity and the persistence of two divergent haplogroups of sacsin-like genes in Acropora millepora have been reported. While it was not clear when the two haplogroups have split and whether the haplogroups have persisted in only A. millepora or the other lineages in the genus Acropora. In this study, we analyzed a genomic region containing a sacsin-like gene from Acropora and Montipora species. Higher nucleotide diversity in the sacsin-like gene compared with that of surrounding regions was also observed in A. digitifera. This nucleotide diversity is derived from two divergent haplogroups of a sacsin-like gene, which are present in at least three Acropora species. The origin of these two haplogroups can be traced back before the divergence of Acropora and Montipora (119 Ma). Although the link between exceptionally high genetic variation in sacsin-like genes and functional differences in sacsin-like proteins is not clear, the divergent haplogroups may respond differently to envionmental stressors and serve in the adaptive phsiological ecology of these keystone species.

Genomic analysis of distinct bleaching tolerances among cryptic coral species.

Reef-building coral species are experiencing an unprecedented decline owing to increasing frequency and intensity of marine heatwaves and associated bleaching-induced mortality. Closely related species from the Acropora hyacinthus species complex differ in heat tolerance and in their association with heat-tolerant symbionts. We used low-coverage full genome sequencing of 114 colonies monitored across the 2015 bleaching event in American Samoa to determine the genetic differences among four cryptic species (termed HA, HC, HD and HE) that have diverged in these species traits. Cryptic species differed strongly at thousands of single nucleotide polymorphisms across the genome which are enriched for amino acid changes in the bleaching-resistant species HE. In addition, HE also showed two particularly divergent regions with strong signals of differentiation. One approximately 220 kb locus, HES1, contained the majority of fixed differences in HE. A second locus, HES2, was fixed in HE but polymorphic in the other cryptic species. Surprisingly, non-HE individuals with HE-like haplotypes at HES2 were more likely to bleach. At both loci, HE showed particular sequence similarity to a congener, Acropora millepora. Overall, resilience to bleaching during the third global bleaching event was strongly structured by host cryptic species, buoyed by differences in symbiont associations between these species.

Coral micro- and macro-morphological skeletal properties in response to life-long acclimatization at CO2 vents in Papua New Guinea

This study investigates the effects of long-term exposure to OA on skeletal parameters of four tropical zooxanthellate corals naturally living at CO2 seeps and adjacent control sites from two locations (Dobu and Upa Upasina) in the Papua New Guinea underwater volcanic vent system. The seeps are characterized by seawater pH values ranging from 8.0 to about 7.7. The skeletal porosity of Galaxea fascicularis, Acropora millepora, massive Porites, and Pocillopora damicornis was higher (up to ~ 40%, depending on the species) at the seep sites compared to the control sites. Pocillopora damicornis also showed a decrease of micro-density (up to ~ 7%). Thus, further investigations conducted on this species showed an increase of the volume fraction of the larger pores (up to ~ 7%), a decrease of the intraskeletal organic matrix content (up to ~ 15%), and an increase of the intraskeletal water content (up to ~ 59%) at the seep sites. The organic matrix related strain and crystallite size did not vary between seep and control sites. This multi-species study showed a common phenotypic response among different zooxanthellate corals subjected to the same environmental pressures, leading to the development of a more porous skeletal phenotype under OA.

Broad scale proteomic analysis of heat-destabilised symbiosis in the hard coral Acropora millepora

Coral reefs across the globe are threatened by warming oceans. The last few years have seen the worst mass coral bleaching events recorded, with more than one quarter of all reefs irreversibly impacted. Considering the widespread devastation, we need to increase our efforts to understanding the physiological and metabolic shifts underlying the breakdown of this important symbiotic ecosystem. Here, we investigated the proteome (PRIDE accession # PXD011668) of both host and symbionts of the reef-building coral Acropora millepora exposed to ambient (~ 28 °C) and elevated temperature (~ 32 °C for 2 days, following a five-day incremental increase) and explored associated biomolecular changes in the symbiont, with the aim of gaining new insights into the mechanisms underpinning the collapse of the coral symbiosis. We identified 1,230 unique proteins (774 host and 456 symbiont) in the control and thermally stressed corals, of which 107 significantly increased and 125 decreased in abundance under elevated temperature relative to the control. Proteins involved in oxidative stress and proteolysis constituted 29% of the host proteins that increased in abundance, with evidence of impairment to endoplasmic reticulum and cytoskeletal regulation proteins. In the symbiont, we detected a decrease in proteins responsible for photosynthesis and energy production (33% of proteins decreased in abundance), yet minimal signs of oxidative stress or proteolysis. Lipid stores increased > twofold despite reduction in photosynthesis, suggesting reduced translocation of carbon to the host. There were significant changes in proteins related to symbiotic state, including proteins linked to nitrogen metabolism in the host and the V-ATPase (-0.6 fold change) known to control symbiosome acidity. These results highlight key differences in host and symbiont proteomic adjustments under elevated temperature and identify two key proteins directly involved in bilateral nutrient exchange as potential indicators of symbiosis breakdown.

Coral larval settlement and post-settlement survival facilitated by crustose coralline algae with or without living tissue

Selection of a permanent attachment site of coral larvae can be a critical determinant of recruitment success affecting the structure of coral communities and underpins the ability of coral reef ecosystems to recover from disturbance. Settlement specificity of a threatened coral in Sanya reefs, Acropora millepora, was tested by measuring the larval metamorphosis preferences and post-settlement survival in response to crustose coralline algae (CCA) species Hydrolithon reinboldii and other substrata. In the no-choice experiments, the larvae of A. millepora had similar rates of total metamorphosis with the presence of CCA regardless of the algae tissue being alive or not, and settlement success induced by CCA was higher than by other substrata (tile or glass). In the paired-choice experiments, when CCA was in presence, the coral larvae preferred the surface of the dish and the side of living CCA. In the absence of CCA, total larvae metamorphosis was lower than in the treatments where CCA was present. New recruits of A. millepora had approximately 68% mean survival on all the settlement substrata after 2 weeks maintained in aquaria with flow-through seawater similar to the coral larval sampling site, but with no coral spat survival in the treatments where CCA was absent. However, there were statistical differences between the larvae survival of dead CCA and glass chips treatment and the others where CCA was present. Our results were consistent with the conclusion that some CCA species could facilitate coral larval settlement and post-settlement survivorship, highlighting the importance of substrata selection success for facilitating coral recruitment in the threatened coral reefs.

A review of coral bleaching specimen collection, preservation, and laboratory processing methods.

Under current climate warming predictions, the future of coral reefs is dire. With projected coral reef decline, it is likely that coral specimens for bleaching research will increasingly become a more limited resource in the future. By adopting a holistic approach through increased collaborations, coral bleaching scientists can maximize a specimen’s investigative yield, thus reducing the need to remove more coral material from the reef. Yet to expand a specimen’s utility for additional analytic methods, information on how corals are collected is essential as many methods are variably sensitive to upstream handling and processing. In an effort to identify common practices for coral collection, sacrifice, preservation, and processing in coral bleaching research, we surveyed the literature from the last 6.5 years and created and analyzed the resulting dataset of 171 publications. Since January 2014, at least 21,890 coral specimens were collected for bleaching surveys or bleaching experiments. These specimens spanned 122 species of scleractinian corals where the most frequently sampled were Acropora millepora, Pocillopora damicornis, and Stylophora pistillata. Almost 90% of studies removed fragments from the reef, 6% collected skeletal cores, and 3% collected mucus specimens. The most common methods for sacrificing specimens were snap freezing with liquid nitrogen, chemical preservation (e.g., with ethanol or nucleic acid stabilizing buffer), or airbrushing live fragments. We also characterized 37 distinct methodological pathways from collection to processing of specimens in preparation for a variety of physiological, -omic, microscopy, and imaging analyses. Interestingly, almost half of all studies used only one of six different pathways. These similarities in collection, preservation, and processing methods illustrate that archived coral specimens could be readily shared among researchers for additional analyses. In addition, our review provides a reference for future researchers who are considering which methodological pathway to select to maximize the utility of coral bleaching specimens that they collect.

Microbiomes of Healthy and Bleached Corals During a 2016 Thermal Bleaching Event in the Upper Gulf of Thailand

Global warming has caused elevated seawater temperature and coral bleaching, including events on shallow reefs in the upper Gulf of Thailand (uGoT). Previous studies have reported an association between loss of zooxanthellae and coral bleaching. However, studies on the microbial diversity of prokaryotes and eukaryotes (microbiome) as coral holobionts are also important and this information is still limited in the uGoT. To address this shortcoming, this report provided baseline information on the prokaryotic (bacteria and archaea) and eukaryotic microbes of healthy and bleached colonies of four prevalent corals Acropora humilis, Acropora millepora, Platygyra sinensis, and Porites lutea and surrounding seawater and sediments, using 16S and 18S rRNA gene next-generation sequencing. Both prokaryotic and eukaryotic microbes showed isolated community profiles among sample types (corals, sediment, and seawater) (ANOSIM: P < 0.001, R = 0.51 for prokaryotic profiles and P < 0.001, R = 0.985 for eukaryotic microbe profiles). Among coral species, P. sinensis showed the most diverse prokaryotic community compared with the others (ANOSIM: P < 0.001, R = 0.636), and P. lutea showed the most diverse eukaryotic microbes (P = 0.014, R = 0.346). Healthy and bleached corals had some different microbiomes in species and their prevalences. For instance, the significant increase of Alphaproteobacteria in P. sinensis resulted in reduced prokaryotic community evenness and altered potential metabolic profiles (i.e., increased amino acid metabolism and genetic information processing and transcription, but decreased prokaryotic functions in cell motility, signaling, and transduction). For eukaryotic microbes, the loss of the algal Symbiodinium (colloquially known as zooxanthellae) in bleached corals such as P. lutea resulted in increased Chromista and Protista and, hence, clearly distinct eukaryotic microbe (including fungi) communities in healthy vs. bleached colonies of corals. Bleached corals were enriched in bacterial pathogens (e.g., Acinetobacter, Helicobacter, Malassesia, and Aspergillus) and decreased coral-beneficial prokaryotic and eukaryotic microbes (e.g., Rhizobiales and Symbiodinium). Additionally, this study identified microbiome species in bleached P. lutea that might help bleaching recovery (e.g., high abundance of Rhizobiales, Oceanospirillales, Flavobacteriales, and Alteromonadales). Overall, our coral-associated microbiome analyses identified altered diversity patterns of bacteria, archaea, fungi, and eukaryotic microbes between healthy and bleached coral species that are prevalent in the uGoT. This knowledge supports our ongoing efforts to manipulate microbial diversity as a means of reducing the negative impacts of thermal bleaching events in corals inhabiting the uGoT.

Combined effects of climate change and the herbicide diuron on the coral Acropora millepora

The Great Barrier Reef (GBR) is threatened by climate change and local pressures, including contaminants in nearshore habitats. This study investigated the combined effects of a GBR-relevant contaminant, the herbicide diuron, under current and two future climate scenarios on the coral Acropora millepora. All physiological responses tested (effective quantum yield (ΔF/Fm′), photosynthesis, calcification rate) were negatively affected with increasing concentrations of diuron. Interactive effects between diuron and climate were observed for all responses; however, climate had no significant effect on ΔF/Fm′ or calcification rates. Photosynthesis was negatively affected as the climate scenarios were adjusted from ambient (28.1 °C, pCO2 = 397 ppm) to RCP8.5 2050 (29.1 °C, pCO2 = 680 ppm) and 2100 (30.2 °C, pCO2 = 858 ppm) with EC50 values declining from 19.4 to 10.6 and 2.6 μg L−1 diuron in turn. These results highlight the likelihood that water quality guideline values may need to be adjusted as the climate changes.

Rapid regeneration of Acropora millepora coral recruits after physical damage to the primary polyp

High post-settlement mortality is thought to be a major limiting factor for the recovery of disturbed coral reef populations, as newly settled corals face a range of physical, chemical, and biological interactions that can inhibit their development. During recruitment, physical interactions are common, with recruits settling on loose substrates likely to be abraded during storm events, while incidental grazing and predation on exposed surfaces may also inflict damage. Nevertheless, larvae have been observed to recruit and survive on substrates where physical damage is likely, possibly owing to their regenerative capacity. Here, we present the first visual time-series evidence of recruit regeneration following physical damage. To investigate regeneration of these recruits, we sliced and removed tissue from individual Acropora millepora coral recruits and tracked their recovery through survivorship and linear growth. Coral recruits were very robust to slicing, even if the mouth-stomodeum was damaged, which does not support the previously held view that damage to this area is terminal. While section removal did show some evidence of damage at later stages, recruits were more robust to damage than expected which may assist their survival in dynamic habitats.

Species-Specific Variations in the Metabolomic Profiles of Acropora hyacinthus and Acropora millepora Mask Acute Temperature Stress Effects in Adult Coral Colonies

Coral reefs are suffering unprecedented declines in health state on a global scale. Some have suggested that human assisted evolution or assisted gene flow may now be necessary to effectively restore reefs and pre-condition them for future climate change. An understanding of the key metabolic processes in corals, including under stressed conditions, would greatly facilitate the effective application of such interventions. To date, however, there has been little research on corals at this level, particularly regarding studies of the metabolome of Scleractinian corals. Here, the metabolomic profiles [measured using 1H nuclear magnetic resonance spectroscopy (1H NMR) and ultra-high-performance liquid chromatography-mass spectrometry (LC-MS)] of two dominant reef building corals, Acropora hyacinthus and A. millepora, from two distinct geographical locations (Australia and Singapore) were characterized. We assessed how an acute temperature stress (an increase of 3.25°C ± 0.28 from ambient control levels over 8 days), shifted the corals’ baseline metabolomic profiles. Regardless of the profiling method utilized, metabolomic signatures of coral colonies were significantly distinct between coral species, a result supporting previous work. However, this strong species-specific metabolomic signature appeared to mask any changes resulting from the acute heat stress. On closer examination, we were able to discriminate between control and temperature stressed groups using a partial least squares discriminant analysis classification model (PLSDA). However, in all cases “late” components needed to be selected (i.e., 7 and 8 instead of 1 and 2), suggesting any treatment effect was small, relative to other sources of variation. This highlights the importance of pre-characterizing the coral colony metabolomes, and of factoring that knowledge into any experimental design that seeks to understand the apparently subtle metabolic effects of acute heat stress on adult corals. Further research is therefore needed to decouple these apparent individual and species-level metabolomic responses to climate change in corals.

Comparative sensitivity of the early life stages of a coral to heavy fuel oil and UV radiation

During an oil spill, shallow, tropical coral reefs are likely to be simultaneously exposed to high intensities of ultraviolet radiation (UVR), which can exacerbate the toxicity of petroleum oils. While successful recruitment of corals is critical for reef recovery following disturbances, the sensitivity of several early life stages of coral to petroleum hydrocarbons has not been investigated, particularly for UVR co-exposure. Here we present the first dataset on the relative sensitivity of three early life stages (gametes, embryos and planula larvae) in a model broadcast spawning coral species, Acropora millepora, to the dissolved fraction of a heavy fuel oil (HFO), both in the absence and presence of UVR. All early life stages were negatively impacted by HFO exposure but exhibited distinct sensitivities. Larval metamorphosis was the most sensitive endpoint assessed with a 10% effect concentration of 34 μg L−1 total aromatic hydrocarbons (TAH) in the absence of UVR. The impact on fertilisation success was highly dependent on sperm density, while the fragmentation of embryos masked embryo mortality. Larval metamorphosis was conclusively the most reliable endpoint for use in risk assessments of the endpoints investigated. Putative critical target lipid body burdens (CTLBBs) were calculated for each life stages, enabling a comparison of their sensitivities against species in the Target Lipid Model (TLM) database. A. millepora had a putative CTLBB of 4.4 μmol g−1 octanol for larval metamorphosis, indicating it is more sensitive than any species currently included in the TLM database. Coexposure to UVR reduced toxicity thresholds by 1.3-fold on average across the investigated life stages and endpoints. This increase in sensitivity in the presence of UVR highlights the need to incorporate UVR co-exposure (where ecologically relevant) when assessing oil toxicity thresholds, otherwise the risks posed by oil spills to shallow coral reefs are likely to be underestimated.

Differences in genetic diversity and divergence between brooding and broadcast spawning corals across two spatial scales in the Coral Triangle region

The Coral Triangle region contains the world’s highest marine biodiversity, however, these reefs are also the most threatened by global and local threats. A main limitation that prevents the implementation of adequate conservation measures is that connectivity and genetic structure of populations is poorly known. The aim of this study was to investigate the genetic diversity, population structure and connectivity patterns of tropical corals in Indonesia on two different spatial scales, as well as by comparing two different reproduction strategies. Genotyping was based on microsatellite markers for 316 individual Seriatopora hystrix colonies and 142 Acropora millepora colonies sampled in Pulau Seribu and Spermonde Archipelago in 2012 and 2013. Differences in allelic diversity and a strong signature of divergence associated with historical land barriers at the Sunda Shelf were found for the brooding coral Seriatopora hystrix. However, differences in diversity and divergence were not pronounced in the broadcast spawning coral Acropora millepora. Within Spermonde Archipelago, two groups were identified: (1) sites of the sheltered inner-shelf and mid-shelf, which were found to be highly interconnected and (2) mid-shelf and outer-shelf sites characterised by higher differentiation. These patterns of contemporary dispersal barriers and genetic diversity can be explained by the differences in life history of the corals, as well as by oceanographic conditions facilitating larval dispersal. The contemporary dispersal barriers found within the Spermonde Archipelago emphasise the need for incorporating connectivity data in future conservation efforts.