Coral Acropora Research Articles

Exposure at low tide leads to a different microbial abundance of intertidal coral Acropora pulchra

ABSTRACT Corals thrive in symbiotic relationships with a variety of microorganisms, including endosymbiont algae. The interaction between coral and microbial associations has been extensively researched since it is thought to play a function in coral health. Temperature and light are two abiotic elements that contribute to coral life. Corals in reef-flat environments frequently face variations in these two characteristics due to their proximity to shallow seas. This study aims to compare the microbial diversity and abundance associated with the coral Acropora pulchra on the reef flat under two conditions, namely corals that emerged to the surface at low tide (SF) and corals that submerged over time (SM) and to compare the microbial diversity of both with those found in its adjacent seawaters. Microbial analysis on 16S rRNA region V4 showed that the alpha diversity of coral microbial communities and seawaters was not significantly different. However, differences in abundance were noticed at the phylum and genus levels. With p-value < 0.05, PCoA analysis using the Bray–Curtis test showed that the coral microbial community was significantly different from the surrounding seawaters. This study indicates that under different conditions, corals of the same species can be dominated by different microbial groups. This study also confirms the uniqueness between coral microbes and their adjacent seawaters. The abundance of certain microbes is a host mechanism for survival.

Coral holobiont research needs spatial analyses at the microbial scale.

Coral holobiont research needs spatial analyses at the microbial scale.

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.

Deoxygenation lowers the thermal threshold of coral bleaching

Exposure to deoxygenation from climate warming and pollution is emerging as a contributing factor of coral bleaching and mortality. However, the combined effects of heating and deoxygenation on bleaching susceptibility remain unknown. Here, we employed short-term thermal stress assays to show that deoxygenated seawater can lower the thermal limit of an Acropora coral by as much as 1 °C or 0.4 °C based on bleaching index scores or dark-acclimated photosynthetic efficiencies, respectively. Using RNA-Seq, we show similar stress responses to heat with and without deoxygenated seawater, both activating putative key genes of the hypoxia-inducible factor response system indicative of cellular hypoxia. We also detect distinct deoxygenation responses, including a disruption of O2-dependent photo-reception/-protection, redox status, and activation of an immune response prior to the onset of bleaching. Thus, corals are even more vulnerable when faced with heat stress in deoxygenated waters. This highlights the need to integrate dissolved O2 measurements into global monitoring programs of coral reefs.

Analisis densitas Zooxanthella pada karang Acropora sp di Perairan Pulau Talam Tapanuli Tengah Provinsi Sumatera Utara

Coral reefs are a unique ecosystem of tropical waters that have physical function as a beach protector with its nature that can reduce the energy of waves moving towards the coast. Coral reef ecosystems are a good places for spawning, nurturing and food sources for fish. The aim of this research was to determine the density of zooxanthella on coral Acropora sp based on different depths. The method that used in this research was a survey method by taking coral samples using purposive sampling technique, then the samples were analyzed and the data was discussed descriptively at the Marine Biology Laboratory, Faculty of Fisheries and Marine, Riau University. The results of this research on the waters of Talam Island obtained a brightness up to 100% of depth, a current velocity was 0.05–0.10 m/s, temperature ranging from 30-32 0C, salinity of 34 o/oo and pH ranging from 7.2–7.6. The corals that used as research objects for zooxanthella density were taken at a depth of 3 m, 5 m, and 7 m, namely the coral Acropora sp. The results showed that the average zooxanthella density on Acropora sp coral at a depth of 3 meters was 6.35x106 cells/cm2, a depth of 5 meters was 2.63x106 cells/cm2, and 1.95x106 cells/cm2 at a depth of 7 meters. Based on observations, the density zooxanthella was decreased by increasing depth.

Spatial and diel patterns of volatile organic compounds, DMSP-derived compounds, and planktonic microorganisms around a tropical scleractinian coral colony

Volatile organic compounds (VOCs) are constituents of marine ecosystems including coral reefs, where they are sources of atmospheric reactivity, indicators of ecosystem state, components of defense strategies, and infochemicals. Most VOCs result from sunlight-related processes; however, their light-driven dynamics are still poorly understood. We studied the spatial variability of a suite of VOCs, including dimethylsulfide (DMS), and the other dimethylsulfoniopropionate-derived compounds (DMSPCs), namely, DMSP, acrylate, and dimethylsulfoxide (DMSO), in waters around colonies of two scleractinian corals (Acropora pulchra and Pocillopora sp.) and the brown seaweed Turbinaria ornata in Mo’orean reefs, French Polynesia. Concentration gradients indicated that the corals were sources of DMSPCs, but less or null sources of VOCs other than DMS, while the seaweed was a source of DMSPCs, carbonyl sulfide (COS), and poly-halomethanes. A focused study was conducted around an A. pulchra colony where VOC and DMSPC concentrations and free-living microorganism abundances were monitored every 6 h over 30 h. DMSPC concentrations near the polyps paralleled sunlight intensity, with large diurnal increases and nocturnal decrease. rDNA metabarcoding and metagenomics allowed the determination of microbial diversity and the relative abundance of target functional genes. Seawater near coral polyps was enriched in DMS as the only VOC, plus DMSP, acrylate, and DMSO, with a large increase during the day, coinciding with high abundances of symbiodiniacean sequences. Only 10 cm below, near the coral skeleton colonized by a turf alga, DMSPC concentrations were much lower and the microbial community was significantly different. Two meters down current from the coral, DMSPCs decreased further and the microbial community was more similar to that near the polyps than that near the turf alga. Several DMSP cycling genes were enriched in near-polyp with respect to down-current waters, namely, the eukaryotic DMS production and DMS oxidation encoding genes, attributed to the coral and the algal symbiont, and the prokaryotic DMS production gene dddD, harbored by coral-associated Gammaproteobacteria. Our results suggest that solar radiation-induced oxidative stress caused the release of DMSPCs by the coral holobiont, either directly or through symbiont expulsion. Strong chemical and biological gradients occurred in the water between the coral branches, which we attribute to layered hydrodynamics.

Gravitactic Swimming of the Planula Larva of the Coral Acropora: Characterization of Straightforward Vertical Swimming.

Vertical migration as well as horizontal dispersion is important in the ecological strategy of planktonic larvae of sedentary corals. We report in this paper unique vertical swimming behavior of planulae of the reef-building coral Acropora tenuis. Several days after fertilization, most of the planulae stayed exclusively at either the top or the bottom of the rearing tank. A good proportion of the planulae migrated almost vertically between top and bottom with fairly straight trajectories. Planulae sometimes switched their swimming direction via a sharp turn between the opposite directions. Quantitative analyses demonstrated that planulae kept constant speed while swimming either upward or downward, in contrast to frequent changes of direction and speed in horizontal swimming. Statistical comparison of propulsive speeds, estimated from swimming speeds and passive sedimentation, revealed gravikinesis of planulae, where the propulsive speed was significantly greater in downward swimming than upward swimming. The larval density hydrodynamically estimated was 0.25% lower than sea water density, which might be explained by the large quantity of lipids in planulae. Also, the deciliated larvae tended to orient oral end-up during floatation, presumably due to asymmetrical distribution of the endogenous light lipids. Plasticity of the larval tissue geometry could easily cause relocation of the center of forces which work together to generate gravitactic-orientation torque and, therefore, abrupt changing of the gravitactic swimming direction. The bimodal gravitactic behavior may give a new insight into dispersal and recruitment of coral larvae.

Aquimarina acroporae sp. nov., isolated from seawater surrounding scleractinian coral Acropora digitifera.

A Gram-stain-negative, aerobic, rod-shaped bacterium (D1M17T) was isolated from the seawater surrounding scleractinian coral Acropora digitifera in Daya Bay, Shenzhen, PR China. Strain D1M17T grew with 0-10 % (w/v) NaCl (optimum, 3-4 %), at 15-37 °C (optimum, 28 °C) and at pH 4.5-8.5 (optimum, pH 7.0-7.5). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain D1M17T formed a lineage within the genus Aquimarina, family Flavobacteriaceae, and it was distinct from the most closely related species Aquimarina salinaria LMG 25375T, Aquimarina gracilis JCM 17453T and Aquimarina spongiae KCTC 22663T with 16S rRNA gene sequence similarities of 97.2, 97.2 and 97.1 %, respectively. The major respiratory quinone was MK-6. The predominant fatty acids (more than 10 %) were iso-C15 : 0 (28.8 %), iso-C17 : 0 3-OH (21.5 %) and iso-C15 : 1 G (13.1 %). The DNA G+C content of D1M17T was 34.4 mol%. The polar lipids in D1M17T comprised one phospholipid and five unknown polar lipids. Phenotypic characteristics (physiological, biochemical and chemotaxonomic) also supported the taxonomic novelty of this isolate. Thus, strain D1M17T is considered to represent a novel species within the genus Aquimarina, for which the name Aquimarina acroporae sp. nov. is proposed. The type strain is D1M17T (=KCTC 92172T= MCCC 1K07224T).

Interaction between the thinly encrusting sponge Clathria venosa and the branched coral Acropora palmata

Interaction between the thinly encrusting sponge Clathria venosa and the branched coral Acropora palmata

New records of sclerozoan fan worms in Acropora sp. from the Gulf of Mannar, south-eastern coast of India (Annelida: Sabellidae)

ABSTRACT Two species, of the sabellid annelid genera Acromegalomma Gil and Nishi, 2017 and Notaulax Tauber, 1879, are reported associated with dead coral (Acropora sp.) in the Gulf of Mannar, south-eastern coast of India. The record for Acromegalomma quadrioculatum (Willey, 1905) constitutes the first report of this species from the Gulf of Mannar, whereas Notaulax pyrrhogaster (Grube, 1878) constitutes the first record of this species in India.

In-situ electro-stimulation enhanced branching but not massive scleractinian coral growth

Calcium carbonate (CaCO3) is the main component of the skeleton of scleractinian corals and is a preferable substrate for attachment and growth. An electro-stimulation method based on the electrolysis of seawater, which generates calcium and magnesium minerals as a crystalline coating over artificial metal structures, was used to boost coral growth during the 1970s. Few studies have attempted to compare survival and growth between electro-stimulated corals and non-electro-stimulated corals in situ. In this study, we used 2D image analysis to quantify the growth of branching and massive corals on electro-stimulated structures. Among four metallic structures that were deployed in Sabang, Aceh, Indonesia, three were electro-stimulated (12 V) and one was used as a control. Two branching corals (Acropora gemmifera and Pocillopora verrucosa) and two massive coral species (Porites murrayensis and Porites lobata) were selected. A total of 256 fragments, comprising 128 fragments derived from two branching species and 128 fragments derived from two massive species, were randomly dispatched to each structure. Underwater photographs were taken at three intervals from August 2019 to December 2020. The results showed that the survival rates (excluding lost fragments) of branching corals under electro-stimulation were approximately 19% higher than massive. However, no significant difference was found between the survival rates of the treatment and control groups for both branching and massive corals. Furthermore, we found that under electro-stimulation, branching corals grew faster than controls but not massive. Our study provides pieces of evidence for the potential use of electrochemical processes in stimulating the growth of branching corals.

Gregarious larval settlement mediates the responses of new recruits of the reef coral Acropora austera to ocean warming and acidification

Gregarious larval settlement represents an important window for chimera formation in reef corals, yet it remains largely unknown how aggregated settlement and early chimerism could modify the performance and responses of coral recruits under elevated temperature and pCO2. In this study, single and aggregated recruits of the broadcast spawning coral Acropora austera were exposed to contrasts of two temperatures (28 versus 30.5°C) and pCO2 levels (~500 versus 1000 μatm) for two weeks, and algal symbiont infection success, survivorship and growth were assessed. Results showed that symbiont infection success was mainly affected by temperature and recruit type, with reduced symbiont infection at increased temperature and consistently higher infection success in chimeric recruits compared to single recruits. Furthermore, although chimeric recruits with larger areal size had significantly higher survivorship in all treatments, the polyp-specific growth rates were considerably lower in chimeric entities than individual recruits. More importantly, the recruit type significantly influenced the responses of recruit polyp-specific growth rates to elevated temperature, with chimeras exhibiting lowered skeletal lateral growth under elevated temperature. These results demonstrate the benefits and costs associated with gregarious larval settlement for juvenile corals under ocean warming and acidification, and highlight the ecological role of larval settlement behavior in mediating the responses of coral recruits to climate change stressors.

Persistence of phenotypic responses to short-term heat stress in the tabletop coral Acropora hyacinthus.

Widespread mapping of coral thermal resilience is essential for developing effective management strategies and requires replicable and rapid multi-location assays of heat resistance and recovery. One- or two-day short-term heat stress experiments have been previously employed to assess heat resistance, followed by single assays of bleaching condition. We tested the reliability of short-term heat stress resistance, and linked resistance and recovery assays, by monitoring the phenotypic response of fragments from 101 Acropora hyacinthus colonies located in Palau (Micronesia) to short-term heat stress. Following short-term heat stress, bleaching and mortality were recorded after 16 hours, daily for seven days, and after one and two months of recovery. To follow corals over time, we utilized a qualitative, non-destructive visual bleaching score metric that correlated with standard symbiont retention assays. The bleaching state of coral fragments 16 hours post-heat stress was highly indicative of their state over the next 7 days, suggesting that symbiont population sizes within corals may quickly stabilize post-heat stress. Bleaching 16 hours post-heat stress predicted likelihood of mortality over the subsequent 3-5 days, after which there was little additional mortality. Together, bleaching and mortality suggested that rapid assays of the phenotypic response following short-term heat stress were good metrics of the total heat treatment effect. Additionally, our data confirm geographic patterns of intraspecific variation in Palau and show that bleaching severity among colonies was highly correlated with mortality over the first week post-stress. We found high survival (98%) and visible recovery (100%) two months after heat stress among coral fragments that survived the first week post-stress. These findings help simplify rapid, widespread surveys of heat sensitivity in Acropora hyacinthus by showing that standardized short-term experiments can be confidently assayed after 16 hours, and that bleaching sensitivity may be linked to subsequent survival using experimental assessments.

Transcriptome Analysis in a Scleractinian Coral, Acropora tenuis, during the Spawning Season With Reference to the Gonadal Condition.

Synchronous spawning is a striking feature of coral. Although it is important for reproductive success, corals reallocate energy for reproduction to growth when they are damaged by external stimuli. To assess the transcriptome before and after spawning in the scleractinian coral Acropora tenuis, we tagged three colonies (one bleached and two unbleached) in the field around Sesoko Island (Okinawa, Japan) in November 2016, sampled them monthly from May to July 2017, and performed RNA sequencing (RNA-Seq) analysis. Histological analysis revealed that the previously bleached colony possessed gametes in June, by which time the other two colonies had already spawned. In RNA-Seq analyses, multi-dimensional scaling based on gene expression similarity among the samples reflected the differences between colonies and between months except for the sample of a non-spawned colony in May, which was similar to the samples in June. The similarity of the non-spawned colony sample in May to the samples in June was also shown in hierarchical clustering based on the expression patterns of the genes that were differentially expressed between months in the spawned colonies. These results suggest that non-spawning was already decided in May, and that the physiological condition in a non-spawned colony in May was advanced to June. RNA-Seq analysis also showed that genes related to gametogenesis and those related to apoptosis were upregulated before and after spawning, respectively.

Halo- and Thiocarbazomycins from Coral- and Coral Reef Sands-Derived Actinomycetes.

Four actinomycete strains isolated from the coral Acropora austera and coral sand samples from the South China Sea, were found to produce a series of halogenated compounds baring similar ultraviolet absorption based on the analysis of HPLC and LC-MS. The production titers of halogenated compounds from Streptomyces diacarni SCSIO 64983 exceeded those of other similar strains leading us to focus on SCSIO 64983. Four new thiocarbazomycins A–B (1–2), chlocarbazomycin E (3), and brocarbazomycin A (4), together with three known chlocarbazomycins A–C (5–7) containing a carbazole core were identified, and their structures were determined using a combination of spectroscopic analysis including HRESIMS, 1D and 2D NMR. Structurally speaking, compounds 1 and 2 have the rare sulfur-containing carbazole nuclei, and 3 and 4 contain Cl and Br atoms, respectively. Although these compounds have not yet been found to have obvious biological activity, their discovery highlights the role of molecular libraries in subsequent drug discovery campaigns.

Varied spawning patterns of reef corals in Nha Trang Bay, Vietnam, western South China Sea

Nha Trang Bay is located in the south-central waters of Vietnam and forms part of the most diverse region within the western South China Sea. Oceanographic studies indicate that this coastal area is not influenced by cold water masses from the north in winter but is subjected to summer upwelling. Coral spawning patterns of four species were monitored by collecting samples of colonies at Hon Mieu Island (12°11’37.31”N and 109°14’1.82”E) and two nearby sites during 2016–2019. Mature eggs were recorded inside polyps Acropora florida and A. robusta branches sampled prior to and after the full moon of late March to early April in 2018, and March in 2019. Spawning for both species was inferred to have occurred 6–8 nights after full moon in early April 2018, and 2–3 nights after full moon for A. robusta in March 2019. Colonies of the tabulate coral A. hyacinthus were inferred to have spawned between 6–11 nights after the full moon of March 2019, up to six nights after the spawning of A. robusta. In contrast, the spawning time of the massive coral of Dipsastraea pallida occurred one month later than that of branching Acropora corals, during the period before and after the full moon of late April to early May in 2018, and 4–5 nights after the full moon in April 2019. Monitoring of the ratio of pigmented mature eggs over time and inferred spawning periods of the three Acropora species and D. pallida indicated that spawning of corals in Nha Trang Bay occurs over an extended spawning period from March to May. Therefore, spawning in these species does not appear to be concentrated during a short mass spawning period over a few nights.

Habitat health, size and saturation do not alter movement decisions in a social coral reef fish

While habitat is often a limiting resource for group-living animals, we have yet to understand what aspects of habitat are particularly important for the maintenance of sociality. As anthropogenic disturbances rapidly degrade the quality of many habitats, site-associated animals are facing additional stressors that may alter the trade-offs of moving or remaining philopatric. Here we examined how habitat health, size and saturation affect movement decisions of a coral-dwelling goby, the five-lined coral goby, Gobiodon quinquestrigatus , that resides within bleaching-susceptible Acropora coral hosts. To assess effects of habitat health, we translocated individuals far from their home corals into dead corals with the choice of adjacent healthy corals. To assess effects of habitat size and saturation, we manipulated coral sizes and the number of residents in healthy corals. Remarkably, 55% of gobies returned home regardless of treatment, 7% stayed in the new coral, and the rest were not found. Unlike other coral reef fishes, habitat factors did not affect how costs of movement influence group-living decisions in this species. These obligate coral-dwelling fishes preferred to home instead of choosing alternative habitat, which suggests a surprising awareness of their ecological surroundings. However, disregarding alternative high-quality habitat is concerning as it may affect population persistence under conditions of rapid habitat degradation. • Not all social animals make the same movement decisions related to their habitat. • We tested the influence of habitat size, health and saturation on movement of fish. • Gobiodon risk high predation costs to go home instead of choosing adjacent habitat. • Gobiodon are unlike other social coral reef fishes, which prefer adjacent habitat. • Habitat and conspecific familiarity are key in the movement decisions of Gobiodon.

Reef fishes weaken dietary preferences after coral mortality, altering resource overlap.

The direct and indirect effects of climate change can affect, and are mediated by, changes in animal behaviour. However, we often lack sufficient empirical data to assess how large-scale disturbances affect the behaviour of individuals, which scales up to influence communities. Here, we investigate these patterns by focusing on the foraging behaviour of butterflyfishes, prominent coral-feeding fishes on coral reefs, before and after a mass coral bleaching event in Iriomote, Japan. In response to 65% coral mortality, coral-feeding fishes broadened their diets, showing a significant weakening of dietary preferences across species. Multiple species reduced their consumption of bleaching-sensitive Acropora corals, while expanding their diets to consume a variety of other coral genera. This resulted in decreased dietary overlap among butterflyfishes. Behavioural changes in response to bleaching may increase resilience of coral reef fishes in the short term. However, coral mortality has reduced populations of coral-feeders world-wide, indicating the changes in feeding behaviour we document here may not be sufficient to ensure long-term resilience of butterflyfishes on coral reefs.

Growth and foraging behavior of hatchery propagated long-spined sea urchins, Diadema antillarum: Implications for aquaculture and restocking

Stocking hatchery propagated long-spined sea urchins Diadema antillarum is a priority option for recovery of this keystone herbivore on Caribbean reefs. However, information on captive culture of D. antillarum is very limited due to historical lack of successful juvenile production from gametes in the hatchery. In this study, hatchery propagated D. antillarum juveniles were cultured using two diets, commercially available herbivore pellets and dried nori, with the presence/absence of stony coral Acropora cervicornis skeleton to understand how diet and habitat complexity affect growth and behavior of juveniles. Juvenile urchin growth, and the diel pattern of feeding and foraging behavior were significantly affected by diet type. Juveniles fed dried nori gained significantly higher live weight and test diameter than those fed herbivore pellets. Juvenile urchins displayed nocturnal feeding and foraging behavior irrespective of diet types and presence/absence of coral structure. Presence/absence of coral structure did not affect growth and diel pattern of feeding and foraging behavior, but modulated habitat usage patterns. Survival of juveniles was neither affected by diet types nor the presence/absence of coral structure. This study concludes that dried nori is a superior diet to herbivore pellets for juvenile urchin culture. Since the presence of coral structure influenced habitat usage patterns, provision of rugose structure in captivity has the potential to convey the innate shelter seeking behavior of juvenile urchins.

Hydrodynamic drivers of fine‐scale connectivity within a coral reef atoll

AbstractAn accurate representation of physical and biological processes is crucial to resolve larval dispersal pathways and characterize connectivity of coral reef ecosystems. We investigate how hydrodynamic forcings drive larval retention rates during the bi‐annual mass coral spawning of the coral genus Acropora within a coral reef atoll (Mermaid Reef), located off northwestern Australia. By analyzing hydrodynamic conditions during 41 yr of historical spring and autumn coral spawning events, we identify typical and extreme hydrodynamic forcing conditions. Particle tracking using the output from a fine‐scale coupled wave‐flow hydrodynamic model forced with typical hydrodynamic conditions during coral spawning, revealed a mean transport of larvae eastward across the atoll. Transport was mainly driven by a combination of wave and tidal currents, where the residual tidal flow and unidirectional wave flow increased the net export of particles, and the oscillatory tidal (non‐residual) flow reduced the net export of particles from the reef. Importantly, however, numerical simulations forced with extreme hydrodynamic conditions generated by episodic tropical cyclones (11 out of 41 yr) showed large deviations from the typical eastward flow during autumn spawning, generating different connectivity pathways within the reef. Considering the substantial time larvae can be retained within reef systems, overlooking fine‐scale hydrodynamic processes may greatly overestimate larval transport distances between adjacent coral reef atolls. As a result, we emphasize the need to consider fine‐scale hydrodynamic processes within regional connectivity predictions, which is generally not considered yet critical to understand the capacity of reefs to recover following disturbances.