Posts Tagged 'corals'

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Tiny cup corals show accelerating ocean acidification in the Salish Sea (radio)

Published 24 December 2025 Media coverage Closed
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Ocean acidification is sometimes described as climate change’s evil twin. The ocean absorbs carbon dioxide from fossil fuel emissions, causing the water to become more corrosive.  

“Ocean acidification is already impacting the growth of oysters, clams, plankton, which in turn are important food sources for salmon, seabirds and other marine organisms,” said Mary Margaret Stoll, who just received her Ph.D. from the University of Washington and is the lead author on a new study of ocean acidification, published in the journal Nature Communications.

Stoll said her love of chemistry, physics and biology led to a fascination with ocean acidification. She joined a project that was looking broadly at how ocean acidification is unfolding in the Salish Sea, which borders British Columbia and Washington state. The wind and ocean currents here cause regular upwellings of carbon rich waters from the deep, influenced by the powerful California Current that causes similar conditions off that coast.

To better understand the region’s chemical trajectory, Stoll got to work with a set of artifacts that were collected 130 years ago: the skeletons of native orange cup corals. Naturalists aboard the USS Albatross — a tall ship on a mission to survey halibut for the federal government — had the foresight to keep them.

Stoll said she’s still amazed that this un-commissioned collection was available to her in the archives of the Smithsonian.

“These corals were incredibly well preserved, and there was so much information attached to them as well — about the depths of collection and where they were collected, and when they were collected, how they were cleaned and preserved,” Stoll said.

Stoll and her team painstakingly practiced their knife skills before slicing tiny samples from the 130-year-old specimens in their lab at the University of Washington. Then, they followed the path that the USS Albatross had sailed through the Salish Sea to get modern coral samples that matched those locations, depths and species.

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Differing proteome responses to ocean acidification between two common pocilloporid corals

Published 24 December 2025 Science Closed
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Ocean acidification threatens coral reef ecosystems by challenging calcification processes fundamental to reef accretion. Yet many corals continue to calcify under elevated pCO2, suggesting species-specific physiological plasticity and potential cellular compensations. Here, we use label-free quantitative proteomics to investigate proteomic responses of two common pocilloporid corals, Stylophora pistillata and Pocillopora damicornis, with known differential resistance to ocean acidification after two months at moderate (~ 940 ppm) and high (~ 2,800 ppm) pCO2 compared to the control (~ 480 ppm). S. pistillata exhibited extensive proteomic restructuring under high pCO2, marked by widespread declines of energy-generating pathways, yet selective increase of proteins involved in ion transport, cytoskeletal stability, and stress responses. This indicates a strategy of general metabolic suppression coupled with targeted investment into essential cellular functions, potentially sustaining calcification despite reduced overall metabolic capacity. In contrast, P. damicornis showed much less proteomic adjustment, primarily involving structural proteins and those potentially linked to cellular redox balance, signifying a moderate, targeted strategy for physiological stability. These divergent responses highlight contrasting modes of resistance (plasticity versus stability). Integrated with physiological data, our findings clarify cellular mechanisms controlling calcification, demonstrating the value of proteomics in coral ecophysiology and providing new insights into species-specific vulnerability under future ocean conditions.

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Genotype and symbiont composition rather than environment influence susceptibility to stony coral tissue loss disease in coral restoration broodstock

Published 19 December 2025 Science Closed
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Over the last several decades, Florida’s Coral Reef has been impacted by global and local stressors causing significant declines in living coral with no signs of natural recovery. Ocean warming, ocean acidification, and infectious diseases are major contributors to the precipitous loss of corals within this region. Since 2014, the stony coral tissue loss disease (SCTLD) outbreak has been particularly devastating, causing unprecedented mortality in over 20 massive coral species. As SCTLD is now endemic in the region, and threats from climate change are likely to persist, studying the disease susceptibility of different coral genotypes under future environmental scenarios is vital for effective restoration. Here, we exposed Orbicella faveolata and Pseudodiploria clivosa genotypes to wild colonies showing signs consistent with SCTLD immediately following a 2-month long exposure to ocean warming (OW) and ocean acidification (OA) scenarios. Corals were exposed to SCTLD for 3 weeks while maintaining the environmental treatments. For both species, pre-exposure to OW and OA scenarios did not make corals more susceptible to SCTLD. However, three genotypes hosting higher levels of Breviolum were at increased risk for showing SCTLD signs under these conditions. One O. faveolata genotype was consistently resistant to SCTLD under the different scenarios, suggesting that natural levels of resistance exist in coral restoration broodstock. Understanding why this genotype could withstand exposure to these stressors may be critical for ensuring survival of restored populations into the future.

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Volcanic bubbles in Papua New Guinea a window into coral’s future

Published 9 December 2025 Press releases Closed
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By the end of this century, coral reefs in Australia and around the world could be slower to recover, structurally simpler, and increasingly dominated by fleshy algae as rising carbon dioxide reshapes ocean chemistry.

These are the predictions that new international research – published this week in Communications Biology – is warning against, as scientists present a volley of stark new findings about the current and long-term impact of a process known as ocean acidification.

As the oceans absorb more carbon dioxide from the atmosphere, they are becoming increasingly acidic – eroding the very calcium carbonate skeletons that build coral reefs. Yet despite decades of laboratory studies and ecosystem models, scientists have lacked real-world systems that reflect how entire reef communities respond to these long-term chemical shifts.

Researchers from the Australian Institute of Marine Science (AIMS) have now filled that gap by studying shallow-water reefs naturally bathed in volcanic CO₂. These reefs, located near remote submarine vents in Papua New Guinea’s Milne Bay Province, experience chronic exposure to elevated carbon dioxide, offering scientists a rare preview of the seascapes expected under future emissions scenarios.

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Progressive changes in coral reef communities with increasing ocean acidification

Published 8 December 2025 Science Closed
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Ocean acidification from increasing atmospheric CO2 is progressively affecting seawater chemistry, but predicting ongoing and near-future consequences for marine ecosystems is challenging without empirical field data. Here we quantify tropical coral reef benthic communities at 37 stations with varying exposure to submarine volcanic CO2 seeping, and determine the aragonite saturation state (ΩAr) where significant changes occur in situ. With declining ΩAr, reef communities displayed progressive retractions of most reef-building taxa and a proliferation in the biomass and cover of non-calcareous brown and red algae, without clear tipping points. The percent cover of all complex habitat-forming corals, crustose coralline algae (CCA) and articulate coralline Rhodophyta declined by over 50% as ΩAr levels declined from present-day to 2, and importantly, the cover of some of these groups was already significantly altered at an ΩAr of 3.2. The diversity of adult and juvenile coral also rapidly declined. We further quantitatively predict coral reef community metrics for the year 2100 for a range of emissions scenarios, especially shared socio-economic pathways SSP2-4.5 and SSP3-7.0. The response curves show that due to ocean acidification alone, reef states will directly depend on CO2 emissions, with higher emissions causing larger deviations from the reefs of today.

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Resistance of the cold-water coral Dendrophyllia cornigera to single and combined global change stressors

Published 28 November 2025 Science Closed
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Current knowledge of the consequences on global change in deep marine ecosystems is still limited, especially since environmental pressures do not act separately, and their potential interactions are mostly unknown. Cold-water corals (CWC) play a significant role in the deep sea, being ecosystem engineers supporting high biodiversity. However, global change may impact CWCs, compromising their integrity and survival. In this study, a nine-month aquaria experiment was conducted on the CWC Dendrophyllia cornigera from the NW Iberian Shelf (NE Atlantic Ocean). The aim was to assess the individual and combined effects of elevated temperature (12 vs. 15 °C), low pH (~ 7.99 vs. 7.69 pHT) and low oxygen (~ 6.4 vs. 4.7 mL L−1), based on the IPCC RCP 8.5 scenario. During the experiment, coral survival, skeletal growth, tissue cover and respiration were monitored as response variables. No significant effects were found on any of the response variables for either individual or combined stressors, pointing to the resistance of D. cornigera to different global change scenarios. Such a physiological resistance may support D. cornigera persistence under future conditions where other CWCs with narrower tolerance ranges may face greater limitations. However, further research is needed to assess potential trade-offs to cope with environmental change, which might impact the long-term survival capacity of this species.

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Dynamics of a coral reef system under climate change

Published 28 November 2025 Science Closed
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Highlights

  • It is established that a new a stochastic coral-starfish model with global warming and ocean acidification.
  • It is revealed that the change in global warming has a decisive impact on the dominant position of corals and starfish.
  • It is found that the variation of pH is able to destabilize coral-starfish interactions.

Abstract

The intensification of global warming and ocean acidification are important factors affecting coral reef degradation, however, their impact mechanisms on coral reef system are still unclear. In this paper, we study the dynamics of a stochastic coral-starfish model considering the factors of global warming and ocean acidification, where the stochastic environmental fluctuation is characterized by mean-reverting Ornstein-Uhlenbeck (OU) process. A key advantage of considering global warming and ocean acidification in coral reef systems is that it can accurately describe the dynamic mechanisms of coral-starfish interactions, providing a scientifically reliable theoretical basis for exploring the evolutionary succession of coral reef systems. The main purpose of this paper is to investigate how global warming and ocean acidification affect the dynamic mechanisms of coral reef systems in the presence and absence of stochastic disturbances. Mathematically, we mainly study the critical threshold conditions for the transcritical bifurcation, saddle-node bifurcation, and Hopf bifurcation of deterministic coral reef system, as well as the existence of ergodic stationary distribution, precise expressions of probability density function, persistent in the mean, and stochastic extinction dynamics in stochastic coral reef system, which in turn provide a theoretical basis for numerical simulations. Numerical analysis indicates that the variations of global warming and ocean acidification can generate a great influence on the coral-starfish dynamics with and without OU process. Significantly, it is found that coral growth dominates under the increasing global warming effect, while starfish growth dominates under the decreasing global warming effect in a randomly perturbed environment. Furthermore, the change of pH has capacity to destabilize coral-starfish interactions, while the intensified global warming can lead to the extinction of starfish. These findings may contribute to the studies of potential strategies for protecting coral reef ecosystems under the impact of climate change.

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Acidic oceans are forcing corals to build weaker skeletons

Published 26 November 2025 Press releases Closed
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When scientists raised baby reef-building corals in acidic seawater pushed toward about pH 7.6, the youngsters still built skeletons.

The tiny skeletons were denser yet less stable, so the corals were more likely to snap when waves or animals pushed on them.

Across tropical oceans, reefs depend on countless such skeletons growing, thickening, and locking together.

As ocean acidification deepens, scientists are racing to understand whether coral skeletons can keep pace.

Inside a coral’s first skeleton

The work was led by Dr. Federica Scucchia, a postdoctoral associate at the University of Rhode Island (URI). Her research focuses on biomineralization, the way living organisms build hard mineral structures, in young reef building corals.

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The team combined three-dimensional X-ray scanning with short growth intervals. They also used electron microscopes to see features smaller than a micrometer and to trace tiny crystals.

These tools let them map mineral density, crystal size, and growth zone shapes in Stylophora pistillata, a common Red Sea stony coral.

Under normal pH, the thickening deposits made up most of the skeleton and wrapped around a web of rapid accretion deposits.

Inside those fibers, much of the mineral turned out to be amorphous calcium carbonate, a disordered mineral form that later transforms into crystals. Only a smaller share had already organized into dense calcium carbonate crystals that pack tightly together.

In more acidic water, the pattern shifted in several important ways. Both growth zones became denser overall, and the crystals inside them grew larger, even though the total skeleton volume shrank.

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The larva-Symbiodiniaceae association at risk: putative impacts of climate change on reproduction, dispersal, and recruitment in coral reefs

Published 24 November 2025 Science Closed
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The relationship between invertebrates and Symbiodiniaceae dinoflagellates is the ecological foundation of diverse and productive coral reef ecosystems. Climate change-induced breakdown of this partnership, i.e., bleaching, is repeatedly driving widespread reef degradation. Thus, the future trajectory of this ecosystem depends on the reproduction and dispersal capacity of invertebrate-Symbiodiniaceae symbiosis. This review examines how climate change affects the biology of larvae from three invertebrate phyla—Porifera, Cnidaria, and Mollusca—that host Symbiodiniaceae, focusing on differences in symbiont transmission mode, symbiont location, and the larvae´s reliance on these associations. Due to limited research on Porifera and Mollusca hosts, most knowledge of larvae-Symbiodiniaceae associations stems from coral larvae patterns. The myriads of combinations of genetic and ecophysiologically distinct hosts and symbionts result in highly context-dependent responses to warming, but symbiotic larvae tend to be more susceptible to oxidative stress and show higher mortality than aposymbiotic larvae. While ocean acidification has little direct effect on the algal symbionts, it impacts larvae variably, especially calcifying larvae (e.g., mollusks), which suffer from impaired calcification and higher mortality. Climate change also impairs the reproductive processes of Symbiodiniaceae-bearing invertebrates, reducing gamete output, causing asynchronous spawning, and lowering larval survival. These effects will result in a persistent decline in recruitment with increased larval retention, consequently reducing reef connectivity and genetic diversity, thus weakening ecosystem resilience. This underscores the urgent need to hasten knowledge on larval ecology under climate change and the functional role of symbionts to better inform marine conservation planning and to incorporate larval ecology in the future predictions.

Continue reading ‘The larva-Symbiodiniaceae association at risk: putative impacts of climate change on reproduction, dispersal, and recruitment in coral reefs’

A century of change in the California Current: upwelling system amplifies acidification

Published 19 November 2025 Science Closed
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Predicting the pace of acidification in the California Current System (CCS), a productive upwelling system that borders the west coast of North America, is complex because the anthropogenic contribution is intertwined with other natural sources. A central question is whether acidification in the CCS will follow the pace of increasing atmospheric CO2, or if climate effects and other biogeochemical processes will either amplify or attenuate acidification. Here, we apply the boron isotope pH proxy to cold-water orange cup corals to establish a historic level of acidification in the CCS and the Salish Sea, an associated marginal sea. Through a combination of complementary modeling and geochemical approaches, we show that the CCS and Salish Sea have experienced amplified acidification over the industrial era, driven by the interaction between anthropogenic CO2 and a thermodynamic buffering effect. From this foundation, we project future acidification in the CCS under elevated CO2 emissions. The projected change in pCO2 over the 21st century will continue to outpace atmospheric CO2, posing challenges to marine ecosystems of biological, cultural, and economic importance.

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Newly discovered CO2 (carbon dioxide) vent cave drives r-strategy shift in a Mediterranean aphotoendosymbiotic coral

Published 14 November 2025 Science Closed
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Highlights

  • Characterization of an unexplored CO2 vent cave
  • CO2 vents chemical-physical parameters affect ecological traits of calcifiers
  • Aphotoendosymbiotic solitary coral naturally inhabiting a CO2-rich gas environment.
  • Prolonged acidified conditions did not affect C. inornata growth rate
  • Shift towards an r-demographic strategy in response to acidified conditions

Abstract

Submarine CO2 volcanic vents represent peculiar environments with varying seawater chemical-physical parameters that may affect the ecological traits of calcifying organisms, such as growth and demographic characteristics. The present study focused on exploring the growth and population dynamics of a temperate, solitary and aphotoendosymbiotic coral Caryophyllia inornata (Duncan, 1878) living in a CO2 vent cave at 14 m depth. The volcanic emissions in and around the cave led high levels of pCO2, resulting in lower calcium carbonate saturation state (Ωa: 2.1–2.2) values compared to those observed in the ambient seawater of the Mediterranean Sea, not affected by venting activity. Prolonged acidified conditions (pHT: 7.5) did not affect C. inornata growth rate but resulted in a population with higher percentage of juvenile individuals, lower average ages and a lower age at maximum biomass percentage, thus suggesting a transition in its population dynamics towards an r-demographic strategy. This study provides a detailed characterization of a previously unexplored CO2 vent cave, highlighting the importance of these sites as natural laboratories to offer valuable insights into understanding the full ecological impact of aphotoendosymbiotic corals under ocean acidification.

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Integrative analysis of coral plasticity and adaptations reveals key proteins driving resilience to changes in ocean carbonate chemistry

Published 14 November 2025 Science Closed
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Understanding how corals adapt to changes in seawater carbonate chemistry is crucial for developing effective coral conservation strategies. Research to date has mostly focused on short-term experiments, overlooking long-term evolutionary effects. Here, we investigated the link between short-term stress responses and long-term genetic adaptations in the coral species Porites pukoensis through experiments under varying CO2 and alkalinity conditions. Our results showed that alkalinity enrichment significantly increased coral calcification rates by 35%-45% compared to high CO2 treatment, highlighting the potential of alkalinity enrichment to mitigate acidification impacts. Corals modulated relative expression levels of basic and acidic proteins in response to changes in seawater carbonate chemistry in the stress experiments. Genomic data revealed that this mechanism has been evolutionarily fixed in various organisms adapting to seawater carbonate chemistry. Additionally, both experimental and genomic results showed that extracellular matrix proteins, like collagen with von Willebrand factor type A domain, were modified in response to distinct carbonate environments. Molecular dynamics simulations and in-vitro experiments demonstrated that the structural stability of these proteins contributes to coral resilience under acidified conditions. This study established an integrated framework combining stress experiments, multi-omics analyses, molecular simulations, and in-vitro validation to identify key proteins involved in coral adaptation to acidification.

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Rapid ocean acidification and coral calcification response in the northern South China Sea: insights from δ11B and B/Ca records in Porites coral

Published 30 October 2025 Science Closed
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Abstract

Ocean acidification (OA) threatens coral calcification by reducing the carbonate ion concentration that corals need to build their skeletons. However, assessments of the impacts of long-term OA are scarce, limiting our understanding of the response and acclimatization of corals to high pCO2 levels. Here we present a 42-year (1968–2010) seasonal δ11B and B/Ca records from Porites corals at Dongsha Atoll, located in the northern South China Sea. Our results reveal a rapid decline in seawater pH over this period, at a rate of −0.0021 ± 0.0008 pH units per year. Of special interest is that the interannual variability in seawater pH appears to be primarily co-regulated by hydrological changes in the Pearl River and fluctuations in the strength of Kuroshio intrusion. These factors are linked to large-scale climate systems and interannual-to-decadal variability, including the Pacific Decadal Oscillation, El Nino-Southern Oscillation, and East Asian Winter Monsoon. Meanwhile, reconstructed carbonate chemistry from the coral calcifying fluid suggests that Porites corals at Dongsha Atoll are able to physiologically modulate their internal pH. This up-regulation of internal pH not only buffers seasonal fluctuations in the aragonite saturation state and sustains stable calcification rates year-round, but also aids in long-term resistance to the detrimental effects of OA.

Plain Language Summary

Ocean acidification poses a major threat to coral reefs by reducing the concentration of carbonate ions essential for coral skeleton formation. However, long-term assessments of ocean acidification impacts on coral calcification are scarce, limiting our understanding of coral resilience and their potential for acclimation to ocean acidification. Using a 42-year Porites coral δ11B and B/Ca records, we investigated long-term variability in pHsw and the carbonate chemistry of the coral calcifying fluid (e.g., pHcf and Ωcf) in the northern South China Sea. Our results reveal a significant decline in pHsw over the past four decades. The interannual variability in pHsw is primarily co-modulated by hydrological changes in the Pearl River system and variations in the strength of Kuroshio intrusion. Physiological modulation of pHcf up-regulation in Dongsha corals plays a key role in minimizing seasonal fluctuations in Ωcf, maintaining stable year-round calcification rates, and contributing to their long-term resistance to the adverse effects of ocean acidification over the past 42 years.

Key Points

  • A 42-year δ11B and B/Ca records from Dongsha corals reveals rapid OA and physiological adjustment of calcifying fluid carbonate chemistry
  • Interannual pHsw variability is primarily co-modulated by hydrological changes in the Pearl River and variations in the Kuroshio intrusion
  • Under a rapid OA rate (−0.0021 ± 0.0008 pHsw yr−1), calcifying fluid Ωcf remains constant, suggesting that DSA corals are resistant to OA
Continue reading ‘Rapid ocean acidification and coral calcification response in the northern South China Sea: insights from δ11B and B/Ca records in Porites coral’

Will coral reefs be gone by 2050? How bleaching, acidification, and ocean heating are killing coral reefs (podcast)

Published 21 October 2025 Web sites and blogs Closed
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Twenty-five years ago, a landmark paper warned that the world’s coral reefs could vanish by 2050. Now, halfway to that projected date (and amid ever more frequent coral bleaching events), that grim prediction feels increasingly close to reality. What is the current state of Earth’s coral reefs, and what would happen to our planetary home without them? 

In this episode, Nate is joined by Ove Hoegh-Guldberg, the marine biologist who made this landmark prediction, for an update on the health of coral reefs and the primary ecological stressors driving their decline. Drawing on decades of research, he explains the mechanisms of coral bleaching, the critical biodiversity hotspots that reefs create, and the implications for human populations that depend on these ecosystems. Ove also touches on the emotional impact of witnessing the loss of reefs for the scientists who have dedicated their lives to studying them.

How are human actions increasingly putting pressure on the very ecosystems that support more than one billion people? What would happen to the broader health of the oceans if reefs were to disappear entirely? And most of all, what changes can both individuals and institutions make today to support the health of these vital ecosystems – and in-turn, the well-being of the entire Earth?

Continue reading ‘Will coral reefs be gone by 2050? How bleaching, acidification, and ocean heating are killing coral reefs (podcast)’

Oxidative stress and histological alterations in coral Briareum violacea co-exposed to ocean acidification and microplastic stressors

Published 17 October 2025 Science Closed
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Ocean acidification and microplastic pollution are two major stressors threatening coral health, yet their combined impacts and underlying mechanisms remain poorly understood. This study investigated the combined effects of ocean acidification and microplastics exposure to coral health. Briareum violacea was exposed to pH at 7.7, 7.5, and 7.3 combined with polyethylene microplastic (PE-MP; 50 mg/L) for 21 days. Polyp length and behavioral adaptability were monitored daily, while coral was collected on days 14 and 21 to assess Symbiodiniaceae density, antioxidant enzyme activity, and histopathological alterations. Results showed that combined exposure to different pH (7.7, 7.5, and 7.3) and PE-MP significantly impaired coral condition, reduced polyp length and Symbiodiniaceae density, along with intensified oxidative stress and tissue damage compared to single stressors. These findings underscore coral vulnerability under combined stressors, emphasizing the necessity for future research to address long-term ecological consequences and resilience mechanisms in coral reef ecosystems.

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Corals fine-tune their chemistry to survive in today’s acidic seas

Published 13 October 2025 Press releases Closed
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Some reef-building corals seem to keep making sturdy skeletons even as the ocean grows more acidic. New evidence from long-lived corals suggests they can tweak the chemistry at the site where their skeleton forms, helping them push through conditions that should, in theory, slow them down.

The work, led by CU Boulder researchers and collaborators, looks back over roughly two centuries of rising acidity and finds corals adjusting their internal calcification engine to stay in the game.

Corals adapt to harsh chemistry

“We found that corals were able to regulate the mechanism they use to build and maintain their skeletons despite the ocean becoming more acidic,” said Jessica Hankins, the paper’s first author and a Ph.D. student in the Department of Geological Sciences.

“It’s an unexpected and hopeful signal; however, we need more long-term data to know what it really means.”

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Environmental conditions and carbonate chemistry variability influencing coral reef composition along the Pacific coast of Costa Rica

Published 10 October 2025 Science Closed
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Coral reef development is influenced by a wide variety of factors, including temperature, salinity, nutrient concentrations, and carbonate chemistry. Studies focusing on physicochemical drivers of coral reef distribution and composition in the Eastern Tropical Pacific (ETP) are scarce, and carbonate chemistry and nutrient data for this region are limited. This study measured coral reef composition and physicochemical parameters along the Pacific coast of Costa Rica, over a one-year period at three locations: Santa Elena and Matapalo in the north, and Parque Nacional Marino Ballena in the south. Our results show high seasonal and spatial variability of physicochemical conditions with significant differences mainly explained by inorganic nutrient concentrations, with driving processes also having a strong influence on the variability of carbonate chemistry parameters. Coastal upwelling is the main driver of the seasonal variability in Santa Elena. Comparison of seasonal dissimilarity within locations confirms the presence of a geographical gradient, with stronger influence of the upwelling in Santa Elena relative to Matapalo, where several parameters displayed a lower seasonality and a carbonate system that supports reef development throughout the year. Conversely, in Marino Ballena the river discharges during rainy season exerted a strong control on the seasonal variability. The integrated analysis of coral reef composition and physicochemical parameters suggests that in addition to inorganic nutrients carbonate chemistry also plays a key role in coral distribution. Analyzing the spatial distribution of the main reef builders provides insights into the species-specific tolerance to varying conditions. Pavona clavus is widely distributed in both the northern and southern locations, suggesting that this massive coral is very tolerant to the high variability of physicochemical conditions. The dominant corals in the north (Pavona gigantea and Pocillopora spp.) are highly tolerant to nutrient-enriched cold waters with low aragonite saturation, while one of the main reef-builders in southern locations (Porites cf. lobata) cope better with low salinity, low aragonite saturation and low light intensity caused by river discharges. Understanding the preferences of individual coral species at our study locations can shed light on the environmental factors driving coral reef distribution in other locations of the ETP.

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Coral calcification resistance to acidification is physiologically linked with complex intracellular calcium ion dynamics between host and symbiont cells

Published 8 October 2025 Science Closed
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Coral calcification is a highly complex process with numerous caveats regarding the mechanisms that dictate productivity and function. Ion homeostasis, however, is the foremost physiological process unanimously shared among Scleractinia and essential for calcification. Consequently, changes to the seawater environment may elicit adverse effects on ion homeostasis. With increasing climate shifts, the physicochemical regime of our global ocean is changing rapidly. Responses of coral calcification to physicochemical change prevail in having little uniformity on an unambiguous mechanism of resistance. Therefore, this study chose a relatively tolerant Hawaiian coral, Montipora capitata to focus efforts on understanding ion homeostasis under chemical seawater manipulation designed to limit calcification. Results indicate a physiological hormesis (two-phase adaptive response) of overall coral host gene expression that was not shared with algal symbionts and decoupled from calcification rates. The sole ion homeostatic mechanism shown was calcium ion regulation by both the host and symbiont cells. Calcium ion homeostasis was also found to be mechanistically different between winter and summer seasons. Thus, potentially indicating complex interactions between host and symbiont cells, as well as the ability for M. capitata to promote calcification under stress. Putatively synthesized here are the physiological cascades and mechanisms of resistance to environmental triggers of acidosis and seasonal change. This work provides insight into linking calcium ion homeostasis with coral resistance and aims to suggest this mechanism as biomolecular indicator used in future assessments to compare tolerance.

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Thermal and acidification gradients reveal tolerance thresholds in Pocillopora acuta recruits

Published 1 October 2025 Science Closed
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Ocean warming and acidification are among the biggest threats to the persistence of coral reefs. Organismal stress tolerance thresholds are life stage specific, can vary across levels of biological organisation and also depend on natural environmental variability. Here, we exposed the early life stages of Pocillopora acuta in Kāne‘ohe Bay, Hawai‘i, USA, a common reef-building coral throughout the Pacific, to projected ocean warming and acidification scenarios. We measured ecological, physiological, biomineralisation and molecular responses across the critical transition from larvae to newly settled recruits following 6 days of exposure to diel fluctuations in temperature and pH in Control (26.8°C–27.9°C, 7.82–7.96 pHTotal), Mid (28.4°C–29.5°C, 7.65–7.79 pHTotal) and High conditions (30.2°C–31.5°C, 7.44–7.59 pHTotal). We found that P. acuta early life stages are capable of survival, settlement and calcification under all scenarios. The High conditions, however, caused a significant reduction in survival and settlement capacity, with changes in the skeletal fibre deposition patterns. Although there was limited impact on the expression of biomineralisation genes, exposure to High conditions resulted in strong transcriptomic responses including depressed metabolism, reduced ATP production and increased activity of DNA damage-repair processes, indicative of a compromised metabolic state. Collectively, our findings demonstrate that coral juveniles living in environments with large diurnal fluctuations in seawater temperature and pH, such as Kāne‘ohe Bay, can tolerate exposure to moderate projected increased temperature and reduced pH. However, under more severe environmental conditions, significant negative effects on coral cellular metabolism and overall organismal survival jeopardise species fitness and recruitment.

Continue reading ‘Thermal and acidification gradients reveal tolerance thresholds in Pocillopora acuta recruits’

4D insights into coral biomineralization: effects of ocean acidification on the early skeleton development of a stony coral

Published 24 September 2025 Science Closed
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Coral biomineralization drives the formation of reef structures, but ocean acidification (OA) threatens this process. Coral survival requires effective skeletogenesis in early life stages, through the formation of co joined growth zones: rapid accretion deposits (RADs) and thickening deposits (TDs). Contrasting theories and lack of data on how these zones form hamper our understanding of normal coral growth and under future OA. This study describes growth patterns of RADs and TDs during the early stages of coral calcification under both normal and OA conditions. The work reveals geometric characteristics of RADs and TDs at micro- and sub-micrometer scales, as a basis for learning how OA impacts the early-formed skeletons. By combining material science approaches and Monte-Carlo simulations to model electron interactions that probe mineral phase composition, we show how TDs and RADs form simultaneously, challenging the classical “step-by-step” growth hypothesis. Unexpectedly, under normal pH, TDs comprise ≈65% amorphous calcium carbonate (ACC) and only 35% crystalline aragonite. Under OA, skeletons exhibit higher densities, with only 50% ACC. RADs are underdeveloped under OA, reducing skeletal bending resistance and increasing fracture risk. These findings reveal that the effect of OA on coral skeletogenesis is more complex than previously understood.

Continue reading ‘4D insights into coral biomineralization: effects of ocean acidification on the early skeleton development of a stony coral’

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