Coral Porites Research Articles

Physiological acclimatization in Hawaiian corals following a 22-month shift in baseline seawater temperature and pH

Climate change poses a major threat to coral reefs. We conducted an outdoor 22-month experiment to investigate if coral could not just survive, but also physiologically cope, with chronic ocean warming and acidification conditions expected later this century under the Paris Climate Agreement. We recorded survivorship and measured eleven phenotypic traits to evaluate the holobiont responses of Hawaiian coral: color, Symbiodiniaceae density, calcification, photosynthesis, respiration, total organic carbon flux, carbon budget, biomass, lipids, protein, and maximum Artemia capture rate. Survivorship was lowest in Montipora capitata and only some survivors were able to meet metabolic demand and physiologically cope with future ocean conditions. Most M. capitata survivors bleached through loss of chlorophyll pigments and simultaneously experienced increased respiration rates and negative carbon budgets due to a 236% increase in total organic carbon losses under combined future ocean conditions. Porites compressa and Porites lobata had the highest survivorship and coped well under future ocean conditions with positive calcification and increased biomass, maintenance of lipids, and the capacity to exceed their metabolic demand through photosynthesis and heterotrophy. Thus, our findings show that significant biological diversity within resilient corals like Porites, and some genotypes of sensitive species, will persist this century provided atmospheric carbon dioxide levels are controlled. Since Porites corals are ubiquitous throughout the world’s oceans and often major reef builders, the persistence of this resilient genus provides hope for future reef ecosystem function globally.

Thylakoid fatty acid composition and response to short-term cold and heat stress in high-latitude Symbiodiniaceae

AbstractCoral reefs are restricted to warm waters, but are increasingly threatened by coral bleaching induced by sustained high sea surface temperatures. Coral endosymbiont thermal resilience has been proposed to depend, at least in part, on the lipid composition of their thylakoid membranes, which influences photosynthetic performance under sub- and super-optimal thermal conditions in photosynthetic organisms. Dinoflagellate symbionts of high-latitude coral reefs experience large seasonal changes in temperature, requiring a wide range of thermal tolerance, and so the thermal responses of their membrane lipids are of particular interest. Using gas chromatography–mass spectrometry, we investigated the composition and response to high- and low-temperature stress of thylakoid fatty acids of dinoflagellate symbionts isolated from corals of Lord Howe Island, the world’s southernmost coral reef. We detected genotype-specific differences in the quality of thylakoid fatty acids of two Cladocopium ITS2 consortia/genotypes, C100/118 and C111*, common local symbionts of the corals Pocillopora damicornis and Porites heronensis. The capability to adjust thylakoid fatty acid composition in response to temperature differed between distinct Cladocopium genotypes, and between the same Cladocopium consortium (C100/118) in the same coral species from different locations. Fatty acid adjustments were highly similar in response to short-term cold and heat stresses, with substantial increases in long-chain polyunsaturated fatty acids and a corresponding increase in the ratio of unsaturated to saturated fatty acids, but these changes did not correlate with the quantum yield of photosystem II. The response of thylakoid fatty acid composition to changes in temperature was a function of symbiont genotype, coral host species and, potentially, environmental history. Our data suggest the existence of common responses to high- and low-temperature stresses and that thylakoid fatty acid saturation is an unreliable predictor of photosystem efficiency under thermal stress in dinoflagellate symbionts.

Monsoon signature in corals from the northern Indian Ocean

The Indian monsoon significantly influences the sea surface conditions in the northern Indian Ocean. Corals growing in shallow waters record such monsoon-induced surface water changes. The record of monsoon signatures in the stable isotopic composition of the Porites coral skeleton from the Lakshadweep Islands, off the coast of Southwestern India, has been investigated. Corals record enhanced rainfall periods on the interannual scale along with seasonal changes in the sea surface temperature (SST) in their stable oxygen isotopic composition (δ18O). Inter-colony variability observed in the δ18O of the Lakshadweep corals was studied to decipher the δ18O-SST relation of the region. The carbon isotopic (δ13C) values for the coral show change during the monsoon period. The observed variations in the coral δ13C values are modulated by other processes, along with its photosynthetic activity. The stable isotopic variation from the Lakshadweep coral demonstrated seasonal and interannual scales variability induced by monsoon activity. Thus, past monsoonal variations can be deciphered from long-term coral records from the Lakshadweep region.

Comparative Genomics Reveal the Animal-Associated Features of the Acanthopleuribacteraceae Bacteria, and Description of Sulfidibacter corallicola gen. nov., sp., nov.

Members of the phylum Acidobacteria are ubiquitous in various environments. Soil acidobacteria have been reported to present a variety of strategies for their success in terrestrial environments. However, owing to lack of pure culture, information on animal-associated acidobacteria are limited, except for those obtained from 16S rRNA genes. To date, only two acidobacteria have been isolated from animals, namely strain M133T obtained from coral Porites lutea and Acanthopleuribacter pedis KCTC 12899T isolated from chiton. Genomics and physiological characteristics of strain M133T and A. pedis KCTC 12899T were compared with 19 other isolates (one strain from each genus) in the phylum Acidobacteria. The results revealed that strain M133T represents a new species in a new genus in the family Acanthopleuribacteraceae. To date, these two Acanthopleuribacteraceae isolates have the largest genomes (10.85–11.79 Mb) in the phylum Acidobacteria. Horizontal gene transfer and gene duplication influenced the structure and plasticity of these large genomes. Dissimilatory nitrate reduction and abundant secondary metabolite biosynthetic gene clusters (including eicosapentaenoic acid de novo biosynthesis) are two distinct features of the Acanthopleuribacteraceae bacteria in the phylum Acidobacteria. The absence of glycoside hydrolases involved in plant polysaccharide degradation and presence of animal disease-related peptidases indicate that these bacteria have evolved to adapt to the animal hosts. In addition to low- and high-affinity respiratory oxygen reductases, enzymes for nitrate to nitrogen, and sulfhydrogenase were also detected in strain M133T, suggesting the capacity and flexibility to grow in aerobic and anaerobic environments. This study highlighted the differences in genome structure, carbohydrate and protein utilization, respiration, and secondary metabolism between animal-associated acidobacteria and other acidobacteria, especially the soil acidobacteria, displaying flexibility and versatility of the animal-associated acidobacteria in environmental adaption.

Microbiome Structuring Within a Coral Colony and Along a Sedimentation Gradient

Reef-building corals form complex relationships with a wide range of microbial partners, including symbiotic algae in the family Symbiodiniaceae and various bacteria. These coral-associated communities can be shaped to varying degrees by environmental context. Sedimentation can structure a coral’s microbial community by altering light availability for symbiotic algae, triggering the coral’s stress response, or serving as a reservoir for both pathogenic and essential bacterial and algal symbionts. To examine the influence of sedimentation on a coral’s microbiome, we used 16S rDNA and ITS-2 amplicon sequencing to characterize the bacterial and algal communities associated with the massive scleractinian coral Porites lobata across pairs of sites along a naturally occurring sedimentation gradient in Fouha Bay, southern Guam. Additionally, we investigate the influence of proximity to sediment on the coral colony scale, by sampling from the edge and center of colonies as well as the nearby sediment. The P. lobata colonies associated with several different genotypes of Cladocopium C15 algal symbionts and often harbored different genotypes within a single colony. However, the different Cladocopium genotypes showed no structuring according to colony position or location along the sedimentation gradient. Bacterial communities were largely consistent across the sedimentation gradient, however, some rarer taxa were differentially abundant across sites. Planococcaceae shows higher abundance closer to the river mouth in coral colonies in both the edge and center of colonies. Peredibacter also shows high abundance near the river mouth but only in sediment and the edges of the colony. We find sediment plays a larger role structuring bacterial communities at the colony scale compared to a coral’s position along the sedimentation gradient. Edge communities look more similar to the sediment compared to the center communities and are also enriched in similar pathways such as those involved in nitrogen fixation. We also find center samples to be dominated by Endozoicomonas compared to the edge, supporting a role for this taxon in structuring bacterial communities and limiting bacterial diversity in coral colonies. Together these results show the differential impact sedimentation can have between sections of the coral colony microhabitat.

Growth Patterns and AMS-14C Age Dates of Fossil Corals from Northwest Pacific

This study aims to evaluate the controlling factor/s of coral growth in the northwest Pacific during the Holocene. Here, we present newly acquired growth data and radiocarbon age dates of fossil Porites corals collected from Holocene uplifted marine terraces in Kikaijima, southern Japan and northwest Luzon, Philippines. Carbonate mineral identification using X-ray diffraction (XRD) and scanning electron microscope (SEM) was conducted to screen for any diagenetic alteration in the fossil corals. We used accelerator mass spectrometer (AMS) – 14C dating to determine the absolute age dates of the fossil corals. Well-preserved fossil corals yielded radiocarbon age dates of 3235 ± 20 and 5712 ± 24 cal. yr BP for Kikaijima and 6285 ± 79, 6144 ± 77, 4336 ± 21, 4277 ± 19, 4200 ± 20, and 2972 ± 70 cal. yr BP for northwest Luzon. X-ray imaging of a 5-mm thick coral slab was utilized to measure growth variables. Linear extension rate, skeletal density, and calcification rate of Kikaijima corals are 3.77–8.72 mm/ yr, 1.71–1.87 g/cm3, and 0.70–1.56 g/cm2yr, respectively. Linear extension rate, skeletal density, and calcification rate from northwest Luzon corals are 10.17–17.6 mm/yr, 0.66–1.67 g/cm3, and 0.91–2.81 g/cm2yr, respectively. Average linear extension rate from both sites was significantly and positively related to average calcification rate (r = 0.72, p = 0.019, n = 10). Skeletal density and linear extension rate measured from both sites were inversely related with each other (r = –0.56, p = 0.09, n = 10). Our data suggest that the variations in linear extension rates of fossil corals were influenced by the sea surface temperature (SST) difference between the study sites. However, data from modern corals are still needed to establish the local linear extension rate- SST relationship and to quantitatively evaluate how coral growth changes with respect to SST. Geomorphological, sedimentological, and geochronological studies of Holocene uplifted marine terraces should be conducted to provide the timing of emergence and coral reef development during Holocene.

ANTIBACTERIAL, CYTOTOXICITY, AND BIOSYNTHETIC GENE CLUSTER ANALYSIS OF CORAL-ASSOCIATED ACTINOBACTERIA FROM MENJANGAN BESAR ISLAND, KARIMUNJAWA NATIONAL PARK

Coral-associated actinobacteria have been abundantly reported for their biological properties, particularly as antimicrobial and anticancer agents. This study was carried out to investigate the potential of coral-associated actinobacteria as antibacterial and cytotoxic agents and analyze the biosynthetic gene clusters (BGCs) of the most remarkable isolate. Coral Porites cylindrica was collected from Menjangan Besar Island, Karimunjawa National Park, Indonesia. Based on the antibacterial screening, three out of fifteen isolates demonstrated the potential as antibacterial agents, such as CSM 11, CSM 13, and CSM 18. They were identified as Streptomyces rochei, S. xiamenensis, and S. albus, respectively. There were no crude extracts that demonstrated antibacterial activity. S. rochei CSM 11 from A11 medium showed a strong cytotoxic activity with an IC50 value of 4.50 µg/mL. The antiSMASH analysis described that S. rochei contains 33 clusters with various bioactive compounds.

Whole-Genome Sequencing Highlights Conservative Genomic Strategies of a Stress-Tolerant, Long-Lived Scleractinian Coral, Porites australiensis Vaughan, 1918

Massive corals of the genus Porites, common, keystone reef builders in the Indo-Pacific Ocean, are distinguished by their relative stress tolerance and longevity. In order to identify genetic bases of these attributes, we sequenced the complete genome of a massive coral, Porites australiensis. We developed a genome assembly and gene models of comparable quality to those of other coral genomes. Proteome analysis identified 60 Porites skeletal matrix protein genes, all of which show significant similarities to genes from other corals and even to those from a sea anemone, which has no skeleton. Nonetheless, 30% of its skeletal matrix proteins were unique to Porites and were not present in the skeletons of other corals. Comparative genomic analyses showed that genes widely conserved among other organisms are selectively expanded in Porites. Specifically, comparisons of transcriptomic responses of P. australiensis and Acropora digitifera, a stress-sensitive coral, reveal significant differences in regard to genes that respond to increased water temperature, and some of the genes expanded exclusively in Porites may account for the different thermal tolerances of these corals. Taken together, widely shared genes may have given rise to unique biological characteristics of Porites, massive skeletons and stress tolerance.

Coral perspective on temperature seasonality and interannual variability in the northern South China Sea during the Roman Warm Period

Few reconstructions of sea-surface temperature (SST) have focused on seasonal and interannual variability, two major components of the global climate system, due to the limited temporal resolution of proxies. This study presents a combined 228-year-long, monthly resolved strontium to calcium ratios (Sr/Ca) record covering the period of 2070–1740 a BP (years before 1950 CE (Common Era)) extracted from three U-series-based sub-fossil Porites corals located on the Xisha Islands, northern South China Sea (SCS). The composite time series allowed for accurate assessment of the natural range of SST variations during snapshots of the Roman Warm Period (RWP). Reconstructed SST revealed that the RWP was characterized by cooler conditions compared with the 20th century, consistent with climatic variations in the western Pacific and East Asia. The amplitude of SST seasonality was within the modern range, except for a lower value at 1980–1928 a BP. Interannual variability associated with El Niño–Southern Oscillation (ENSO) activity was enhanced by 39% relative to 1980–2014 CE. The results of the sliding window demonstrate that ENSO variability persistently strengthened during 2070–2010 a BP, followed by an overall fluctuating attenuation during 1980–1928 a BP. Then, the trends of rising first before descending twice during 1852–1800 a BP appeared. Furthermore, ENSO activity played a leading role in steering short-term changes in SST seasonality in the northern SCS, manifested as stronger ENSO activity with more frequent El Niño events and decreased SST seasonality. Considering that the frequency of extreme ENSO events may strengthen in the future under global warming, the climate in the northern SCS might become more variable and complex.

A Century long of coral records of heavy metals in coastal water of Wakatobi Marine National Park, South East Sulawesi

Scleractinian corals absorb heavy metals in their skeletons; therefore, corals can be used as environmental recorders due to incorporating certain metals for centuries. The research was conducted in Wakatobi Marine National Park (WMNP) using a core of massive coral Porites Sp. to determine heavy metals’ concentrations and assess the possible impact on the coastal water. The sample was collected by drilling the coral vertically using a pneumatic tool. Annual banding was determined by using x-ray radiography, continued with sub-sampled from each band, and analyzed using an Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) for heavy metals determination. Enrichment Factor (EF) and Principal Component Analysis (PCA) were applied for assessing possible impact and differentiating between the heavy metals, respectively. The concentrations of heavy metals fluctuated during the period of the year 1917 to 2016, with the average concentration were 0.55 %, 0.07 %, 2.46 ppm, 3.86 ppm, 5.70 ppm, 63.22 ppm, 0.66 ppm, 3.16 ppm, 0.66 ppm, and 42.59 ppm for Sr, Mg, Mn, Ba, Cu, K, Pb, Zn, Cr, and Al, respectively. EF for all heavy metals showed that the coastal area was at the level of very small pollution (EF<2); therefore, it can be used as baseline data.

Linking isotopic signatures of nitrogen in nearshore coral skeletons with sources in catchment runoff

We use a multi-tracer approach to identify catchment sources of nitrogen (N) in the skeletons of nearshore Porites corals within the Great Barrier Reef. We measured δ15N, δ13C and C:N ratios of particulate organic matter (POM) sampled from the Pioneer River catchment and identified five distinct end-members: (1) marine planktonic and algal-dominated matter with higher δ15N values from the river mouth and coastal waters; (2) estuarine planktonic and algal matter with lower δ15N values associated with estuarine mixing; (3) lower river freshwater phytoplankton and algal-dominated matter in stratified reservoirs adjacent to catchment weirs, with the 15N-enriched source likely caused by microbial remineralization and denitrification; (4) upper river low δ15N terrigenous soil matter eroded from cane fields bordering waterways; and (5) terrestrial plant detrital matter in forest streams, representing a low δ15N fixed atmospheric nitrogen source. The δ15N values of adjacent, nearshore Porites coral skeletons is reflective of POM composition in coastal waters, with 15N-enriched values reflective of transformed N during flood pulses from the Pioneer River.

Copper and Zinc isotope signatures in scleratinian corals: Implications for Cu and Zn cycling in modern and ancient ocean

Metal stable isotopes in marine carbonates have been widely used as novel proxies for metal cycling through the geological past. Amongst these metals, copper (Cu) and zinc (Zn) have received great attention owing to their vital roles in metabolic processes. However, whether modern marine biogenic carbonates record the seawater isotope signatures of Cu (δ65Cu) and Zn (δ66Zn) and mechanisms and factors controlling isotope fractionation of these metals remain unclear, hindering applications of both isotope systems in paleoceanography. Here we present annually-resolved records of δ65Cu and δ66Zn in seven coral (Porites) cores sampled from different marine settings in the South China Sea and the Luzon Strait, western Pacific. We find that the aragonitic skeletons of corals are enriched in light Cu but heavy Zn isotopes relative to surface seawaters, with δ65Cu and δ66Zn in the range of −0.16 ± 0.06‰ to 0.40 ± 0.05‰ and 0.06 ± 0.04‰ to 0.46 ± 0.08‰ (2SD), respectively. The coral δ65Cu exhibits significant inter- and intra-colony variations, which are most likely controlled by Rayleigh-type fractionation in the calcifying fluids of corals rather than by changes in environmental factors or seawater δ65Cu. We thus suggest that δ65Cu in ancient carbonates may not be a direct record of Cu isotope compositions in coeval seawaters. In contrast, coral δ66Zn shows insignificant temporal variation, and the Zn isotope fractionation between individual corals and seawaters are relatively small and constant (0.10 ± 0.05‰, n = 33, 2SD). This limited Zn isotope fractionation is much lower than that determined during inorganic precipitation of calcite, which is likely due to pH up-regulation by the coral that changes aqueous Zn speciation, and preferential organic complexation of the heavy Zn isotopes in the calcifying fluids. Therefore, Porites corals are promising archives for tracking historical changes of surface seawater δ66Zn. Our new datasets of reef carbonates, particularly the coral δ65Cu values which are measured for the first time, could provide a better constrain on marine Cu and Zn geochemistry and their modern oceanic mass and isotope budgets.

Physiological Responses of Pocillopora acuta and Porites lutea Under Plastic and Fishing Net Stress

Marine debris has become a global problem affecting coral health around the globe. However, the photophysiological responses of corals to marine debris stress remain unclear. Therefore, this study firstly investigated transparent and opaque plastic bag shading and fishing nets directly contacting the coral. Photosynthetic performance, pigment content, symbiont density, and calcification rate of a branching coral Pocillopora acuta and a massive coral Porites lutea were investigated after 4 weeks of exposure to marine debris. The results show that the maximum quantum yield of PSII significantly decreased in P. lutea with all treatments, while P. acuta showed no effect on the maximum quantum yield of PSII from any treatments. Transparent plastic bag shading does not affect P. acuta, but significantly affected the maximum photochemical efficiency of P. lutea. Photoacclimation of cellular pigment content was also observed under opaque plastic bag shading for both species at week 2. Fishing nets had the strongest effect and resulted in P. acuta bleaching and P. lutea partial mortality as well as a decline in zooxanthellae density. Calcification rate of P. acuta significantly decreased with treatments using opaque plastic bag and fishing net, but for P. lutea only the treatment with fishing net gave any observable effects. This study suggests that the sensitivities of corals to marine debris differ strongly by species and morphology of the coral.

Coral-inferred historical changes of nickel emissions related to industrial and transportation activities in the Beibu Gulf, northern South China Sea

As one of the most abundant metals in heavy oils, Ni has suffered so notably increasing impacts from industrial and traffic activities that anthropogenic Ni emissions have altered natural geochemical processes. The coral Ni/Ca has become a reliable proxy for characterizing marine pollution, but this potential has been unexploited for highlighting oil pollution. Here, we utilized a high-resolution record of geochemical parameters (Ni/Ca, δ18O, and δ13C) in a Porites coral of an offshore island in the northern South China Sea to reconstruct of Ni distribution patterns in surface seawater from 1984 to 2015. The coral Ni/Ca ratios exhibit minor fluctuations, except for multiple mutation peaks (0.20 ± 0.42 μmol/mol) during the period from 1984 to 1993. The ratio was low and stable (0.10 ± 0.09 μmol/mol) from 1994 to 2008, and then increased rapidly with significant variations (1.60 ± 4.56 μmol/mol) from 2009 to 2015. The coral Ni/Ca ratios captured all significant Ni discharges, and this demonstrates its potential for recording oil spill episodes. The historical variations in the contributions of Ni indicate that industrial and traffic activities should be responsible for changes in the anthropogenic input. The leaks and consumptions of petroleum likely account for the primary Ni emission sources.

Dangerous demographics in post-bleach corals reveal boom-bust versus protracted declines

Thermal-stress events have changed the structure, biodiversity, and functioning of coral reefs. But how these disturbances affect the dynamics of individual coral colonies remains unclear. By tracking the fate of 1069 individual Acropora and massive Porites coral colonies for up to 5 years, spanning three bleaching events, we reveal striking genus-level differences in their demographic response to bleaching (mortality, growth, and recruitment). Although Acropora colonies were locally extirpated, substantial local recruitment and fast growth revealed a marked capacity for apparent recovery. By contrast, almost all massive Porites colonies survived and the majority grew in area; yet no new colonies were detected over the 5 years. Our results highlight contrasting dynamics of boom-and-bust vs. protracted declines in two major coral groups. These dangerous demographics emphasise the need for caution when documenting the susceptibility and perceived resistance or recovery of corals to disturbances.

Microbiome of a Reef-Building Coral Displays Signs of Acclimation to a Stressful Shallow Hydrothermal Vent Habitat

Most tropical reef corals live at temperatures near 27°C and pH values near 8. Conditions outside of these can stress corals and lead to bleaching, disease, and death. However, some corals can survive in marginal or extreme habitats outside of these ranges. To date there is a paucity of knowledge about the role that associated microbes may play in the acclimation of corals to such extreme habitats. Here, we explore differences in the compositional and functional profile of the microbiomes of the scleractinian coral Porites panamensis living both on and off potentially stressful shallow-water hydrothermal vents. The environment near the vents is extreme, with temperatures exceeding 80°C and pH values below 6. Coral microbiomes under stress often exhibit increased diversity, increased abundance of pathogenic bacteria, and functional profiles that shift toward pathways associated with pathogenic taxa. Samples from along a transect that crossed an arc of hydrothermal vents were sequenced for the 16S rRNA gene (V4 region). On-vent coral microbiomes were distinct from those of off-vent corals, but did not have increased alpha or beta diversity. On-vent samples had a higher relative abundance of the beneficial endosymbiont, Endozoicomonas. On- and off-vent microbiomes did not differ in overall abundance of the endolithic green alga Ostreobium, however, a single ASV, close to O. quekettii was more abundant in on-vent corals. Ostreobium can provide many of the same benefits to corals as zooxanthellae and their symbiosis is better maintained under thermal stress. Surprisingly, on-vent coral microbiomes had fewer microbial taxa that are known to be pathogenic or associated with stress than did off-vent corals. The predicted functional profiles of on-vent microbiomes revealed enrichment of pathways related to aerobic respiration, fermentation and amino acid biosynthesis, but not of virulence-related pathways. Our results suggest that P. panamensis microbiomes have acclimated to the extreme environment of the hydrothermal vent habitat rather than showing signs of stress. These results exemplify the need to focus efforts on examining the mechanisms of resilience, including symbioses with microbiota, in corals living in extreme environments in an effort to design better management strategies for reef-building corals under thermal and pH stress.

Paleo-earthquake records of the Hengchun offshore structure, southern Taiwan, revealed by uplifted coral colonies

In the southernmost part of Taiwan, the Western Hengchun Tableland is a prominent topographic feature, with several steps of late Pleistocene marine terraces forming the top of the eastward tilting tableland, and uplifted Holocene coral reefs along the coast. An active Hengchun offshore structure, located offshore to the west, was proposed to be the primary formation mechanism of the tableland. However, the presence of this structure is under debate, and some argued that the tableland was formed by aseismic deformations of mud diapirism, because no record of paleo-earthquakes related to the structure was identified. In this study, we utilized fossil coral colonies as paleo-sea-level indicators to identify land-level uplifts and paleo-earthquakes probably produced by this structure over the past 2.5 thousand years. We identified uplifted Porites coral colonies at five sites along the coast and found that they can be separated into six groups based on their elevations and ages. Since the corals in the same age group have similar elevations at one site, and corals found at different sites along the coast can all be correlated into the six groups, these coral colonies likely recorded co-seismic uplifts of six paleo-earthquake events of the proposed Hengchun offshore structure. Co-seismic deformation of this structure is also likely responsible for the long-term topographic development of the Western Hengchun Tableland. Our results suggest that mud diapirism is not the primary structural mechanism in the area, and the Hengchun offshore structure poses significant regional seismic hazard potentials in the future.

Field measurements of a massive Porites coral at Goolboodi (Orpheus Island), Great Barrier Reef

An exceptionally large coral Porites sp. has been identified and measured at Goolboodi (Orpheus Island), Great Barrier Reef (GBR). This coral was measured in March 2021 during citizen science research of coral reefs in the Palm Islands group. We conducted a literature review and consulted scientists to compare the size, age and health of the Porites with others in the GBR and internationally. This is the largest diameter Porites coral measured by scientists and the sixth highest coral measured in the GBR. The health of the Porites was assessed as very good with over 70% live coral cover and minor percentages of sponge, live coral rock and macroalgae. An estimated age of 421–438 years was calculated based on linear growth models. Manbarra Traditional Owners were consulted and suggested that the Porites be named Muga dhambi (big coral) to communicate traditional knowledge, language and culture to indigenous, tourists, scientists and students.

Outplanting of branching Acropora enhances recolonization of a fish species and protects massive corals from predation

Damselfish of the genus Stegastes inhabit territories and cultivate algal gardens on branching corals of the genus Acropora, aggressively protecting their territories from other fish and preventing predation upon corals within the territory. This behaviour has important ecological impacts and could also be useful in reducing predation on outplanted corals during reef restoration efforts. However, the degree of protection from predators may depend on the ability of Stegastes spp. to recolonise outplanted or newly established coral colonies. Protection of bleaching-resilient massive corals within territories may be of particular importance due to the role of these corals in maintaining coral cover following bleaching events. This study examined whether the presence of Stegastes spp. reduces predation on the massive bleaching-resilient coral Porites lutea in the Mauritian lagoon, and whether Stegastes spp. readily colonise outplanted branching coral fragments and provide adjacent massive corals with indirect protection from predation. Predation levels on wild-occurring and outplanted P. lutea within and outside Stegastes spp. territories were measured. In addition, Acropora muricata branches were outplanted adjacent to wild P. lutea colonies outside Stegastes spp. territories, and recolonisation of these outplants by Stegastes spp. and the impacts of recolonisation on predation were monitored. Both wild and outplanted P. lutea colonies within Stegastes spp. territories sustained less predation damage compared to colonies outside territories. Stegastes spp. recolonized outplanted A. muricata colonies within six months of outplanting, and in doing so returned predation protection to adjacent P. lutea colonies. The ability of Stegastes spp. to colonise outplanted corals and provide indirect protection to adjacent massive bleaching-resilient corals may inform coral outplanting efforts in systems where Stegastes spp. are common. Encouraging Stegastes spp. recolonisation may help to reduce predation damage to corals within territories and potentially improve the success of rehabilitation efforts.

Surface pH Record (1990–2013) of the Arabian Sea From Boron Isotopes of Lakshadweep Corals—Trend, Variability, and Control

AbstractAtmospheric CO2 rise in post‐industrial era has resulted in decline in surface ocean pH, commonly known as “ocean acidification (OA),” which has become a threat to marine calcifiers. Instrumental records of ocean pH and its reconstruction utilizing boron isotope (δ11B) composition of corals demonstrate a long‐term OA trend characterized by large spatio‐temporal variability in both Pacific and Atlantic oceans. However, no such record exists to elucidate long‐term OA trend of the Indian Ocean. We report the first sub‐annually resolved pH record (1990–2013) from the Arabian Sea based on δ11B measurements on Porites coral from Lakshadweep coral reefs. This pH record is characterized by large variability ranging from 7.93 to 8.65 with no long‐term discernable trend. The long‐term declining trend expected from the ∼50 ppm increase in atmospheric CO2 during the coral growth interval appears to be obscured by large surface pH variability in the Arabian Sea. Our investigation reveals that physical oceanographic processes for example, upwelling, downwelling and convective mixing modulated by El Niño‐Southern Oscillation (ENSO) largely control surface pH variability and masked expected long‐term OA trend resulting from anthropogenic CO2 rise. Combining the model‐based predictions of increase in frequency and amplitude of ENSO events in a future warming scenario and the observed ENSO dependency of surface water pH, we predict more frequent and large pH variability (“pH extremes”) in this region. Such pH extremes and their occurrences might be critical for the resilience and adaptability of corals and other calcifiers in Arabian Sea and other similar oceanic settings elsewhere.