Posts Tagged 'South Pacific'

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Job: senior programme assistant – early career ocean professionals (ECOP) & ocean acidification monitoring (PIOAC)

Published 27 October 2025 Jobs Closed
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Description

The Pacific Community (SPC) is the principal scientific and technical organisation in the Pacific region, supporting development since 1947. We are an international development organisation owned and governed by our 27 country and territory members. In pursuit of sustainable development to benefit Pacific people, our organisation works across more than 25 sectors. We are known for our knowledge and innovation in such areas as fisheries science, public health surveillance, geoscience, and conservation of plant genetic resources for food and agriculture.

The In commemorating the SPC’s 70th anniversary, the 10th Pacific Community Conference agreed to establish the Pacific Community Centre for Ocean Science (PCCOS) to be hosted at SPC and become a true flagship for scientific excellence and a dedicated regional science information and knowledge hub. PCCOS leads the design of the SPC Ocean Flagship through consultation with SPC divisions and regional partners, as well as coordinating cross-divisional projects, implemented across SPC divisions (FAME, GEM, CCES). PCCOS is also implementing seed-projects/programmes such as the Pacific Islands Ocean Acidification Centre (PIOAC), the Pacific Early Career Ocean Professionals (ECOP) Network and Placement Programme, the Pacific Islands Decade Coordination Centre (PI-DCC), and the Regional Alliance of the Global Ocean Observing System for the Pacific Islands (PIGOOS), that all have regional coordination mandates.

The role – Senior Programme Assistant – Early Career Ocean Professionals (ECOP) & Ocean Acidification Monitoring (PIOAC) will be responsible to support the PCCOS work on Pacific Early Career Ocean Professionals (ECOP), assisting with work of the Pacific Early Career Ocean Professionals (ECOP) Network and Placement Programme. The position will also assist with the coordination of ocean acidification monitoring and capacity-building activities within PCCOS and GEM division in close collaboration with existing activities in other divisions.

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On the measurement of ocean acidity with ambient sound

Published 22 October 2025 Science Closed
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Abstract

The volume-integrated pH of seawater can be determined from the frequency and depth dependence of wind-generated ambient noise in the ocean. Over the 1–10 kHz frequency band, three main processes contribute to the acoustic attenuation in seawater: the chemical relaxation of boric acid and magnesium carbonate (<3 kHz, related to pH) and of magnesium sulfate (>3 kHz, unrelated to pH). When local winds are strong (>10 m/s), the ambient noise is dominated by locally generated surface noise, which exhibits a depth-independent directionality and weak frequency and depth-dependent intensity. By measuring the depth dependence of the spectral slope, the pH may be estimated from a comparison of the experimental data with an analytical model of ambient noise. Wideband (5 Hz–30 kHz) vertical ambient sound profiles were recorded using two- and four-channel free-falling acoustic profilers at depths ranging from 500 m to 10 km during nine deployments in the Philippine Sea, Mariana Trench, and Tonga Trench from 2009 to 2021. Two analytical models of the depth dependence of ambient noise were developed: a simplified linear model valid at depths <1,500 m and a full nonlinear model valid for the deep ocean. Estimates of pH were found by minimizing the mean absolute percent error between the measurements and the models. This method of passive acoustic absorption spectroscopy demonstrates the potential and sources of uncertainty in determining the depth-averaged value of pH. The method could be suitable for the long-term passive acoustic monitoring of ocean acidity.

Plain Language Summary

In this work, we demonstrate that ambient sound in the ocean can be used to measure local, depth-averaged ocean pH. This is possible because the absorption of sound in seawater depends on chemical processes, including the relaxation of boric acid and magnesium carbonate, and has a frequency-dependent sensitivity to the pH. By analyzing the depth dependence of ambient sound over the wind-driven noise-dominated band (1–10 kHz), we can estimate pH through a comparison of measured power spectral slopes with an analytical model. Using measurements from the Philippine Sea, Mariana Trench, and Tonga Trench, carried out from 2009 to 2021 with a free-falling autonomous instrument platform, Deep Sound, we estimated the depth-averaged pH in each location. This technique can be used for long-term passive acoustic monitoring of ocean acidity.

Key Points

  • The depth dependence of the spectral slope of wind-generated noise provides a measurement of the differential acoustic attenuation between 1 and 10 kHz
  • The differential attenuation is used to estimate the depth-integrated pH
  • The proposed method enables long-term volumetric (order of km3) monitoring of ocean acidity
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From small-scale variability to mesoscale stability in surface ocean pH: implications for air–sea CO2 equilibration

Published 10 October 2025 Science Closed
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One important aspect of understanding ocean acidification is the nature and drivers of pH variability in surface waters on smaller spatial (i.e. areas up to 100 km2) and temporal (i.e. days) scales. However, there has been a lack of high-quality pH data at sufficiently high resolution. Here, we describe a simple optical system for continuous high-resolution surface seawater pH measurements. The system includes a PyroScience pH optode placed in a flow-through cell directly connected to the underway supply of a ship through which near-surface seawater is constantly pumped. Seawater pH is measured at a rate of 2 to 4 measurements min−1 and is cross-calibrated using discrete carbonate system observations (total alkalinity, dissolved inorganic carbon, and nutrients). This setup was used during two research cruises in different oceanographic conditions: the North Atlantic Ocean (December 2020–January 2021) and the South Pacific Ocean (February–April 2022). By leveraging this novel high-frequency measurement approach, our findings reveal fine-scale fluctuations in surface seawater pH across the North Atlantic and South Pacific oceans. While temperature is a significant abiotic factor driving these variations, it does not account for all observed changes. Instead, our results highlight the interplay between temperature, biological activity, and waters with distinct temperature–salinity properties and their impact on pH. Notably, the variability differed between the two regions, suggesting differences in the dominant factors influencing pH. In the South Pacific, biological processes appeared to be mostly responsible for pH variability, while in the North Atlantic, additional abiotic and biotic factors complicated the correlation between expected and observed pH changes. While our findings indicate that broader ocean-basin-scale analyses based on lower-resolution datasets can effectively capture surface ocean CO2 variability at a global scale, they also highlight the necessity of fine-scale observations for resolving regional processes and their drivers, which is essential for improving predictive models of ocean acidification and air–sea CO2 exchange.

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Effects of climate change on marine ecosystems in the southeastern Pacific: multiple ocean stressors assessed through climate velocities

Published 3 October 2025 Science Closed
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Anthropogenic climate change (CC) has triggered a cascade of impacts on marine ecosystems, often referred to as the ‘deadly trio’: warming, acidification, and deoxygenation. While these stressors will globally lead to the compression of marine habitats, their regional effects vary significantly and remain understudied. This is particularly true for the southeastern Pacific (SEP), which supports rich pelagic and benthic ecosystems closely linked to a complex seafloor featuring archipelagos and extensive seamount chains. Using model simulations from Phase 6 of the Coupled Model Intercomparison Project, this study examines future regional-scale environmental changes in the SEP. Our analysis builds on the observation that the South Pacific Ocean Gyre is among the regions experiencing the least warming globally and that the epipelagic zone within the oxygen minimum zone (OMZ) may oxygenate in the future. These conditions may promote habitat expansion, which we assess using the climate velocities for temperature, oxygen, and pH. Estimates of climate velocities from the ensemble model mean under a pessimistic near future (2015-2050) yield values ranging from –730 to 449 km/year, exhibiting greater absolute climate velocities for oxygen than pH. Over the longer-term horizon (2015–2100), the area of zones where absolute climate velocity exceeded the 75th percentile increased by 65%, 72%, and 215% for temperature, oxygen, and pH, respectively. The strongest velocities (absolute value) occur in the equatorial sector and in the Humboldt system. While all regions mostly show a climate-driven habitat loss due to surface-to-200 m pH decline, two broad areas benefit from conservation below the surface: a region in the tropics extending from 10°S–100°W to the east of Rapa Nui and the coastal region of Peru and Chile, extending up to the Desventuradas and Juan Fernández archipelagos. While the former is due to the slow warming rates (<2.9 km yr−1), the latter results from both slow deoxygenation and oxygenation climate velocities (between −2.9 and 2.9 km yr−1) along the coast of those countries, a zone that overlaps with the lowest changes in pH in the SEP, giving them a unique conservation value. We demonstrate that epipelagic ecosystems within the OMZ may be less impacted by CC than those outside of it. These findings highlight key areas for conservation under future ocean warming, deoxygenation and pH changes.

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Using boron isotopes to examine calcification fluid pH changes in marine calcifiers under environmental change

Published 23 September 2025 Science Closed
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CO₂-driven ocean acidification (OA) decreases seawater pH and carbonate ion concentrations, which can impact the calcification and physiology of marine calcifiers. These organisms form calcium carbonate skeletons and shells from a specialized calcification fluid that is, to varying degrees, isolated from surrounding seawater. The carbonate structures serve as archives, preserving the chemical signature of the calcification fluid, which can be analyzed using geochemical proxies. In the following thesis, I examine how different taxa respond to future ocean changes by exposing them to predicted future acidification scenarios. Additionally, I aim to understand if an organism’s resilience to the impacts of ocean acidification is linked to their ability to regulate their calcification fluid chemistry using geochemical proxies.

In Chapter 1, I investigate the geochemistry of three reservoirs important for biomineralization – seawater, the extrapallial calcification fluid (EPF), and the shell – of two commercially important bivalve species: Crassostrea virginica and Arctica islandica to understand if the boron isotope proxy is probing calcification fluid pH. Additionally, I examined the effects of three ocean acidification conditions (ambient: 500 ppm, moderate: 900 ppm, and high: 2800 ppm CO2) on the calcification and chemistry of the calcification fluid of the same three reservoirs for C. virginica. Comparisons of seawater and extrapallial fluid geochemistry indicated that the EPF has a distinct composition that differs from seawater. Additionally, our OA experiments show that EPF chemistry is significantly affected by ocean acidification, demonstrating that the biological pathways regulating or storing these ions are impacted by ocean acidification. I also found that shell δ11B does not faithfully record seawater pH, but rather was correlated with EPF pH, despite an offset from in situ microelectrode pH measurements. However, the δ11B-calculated pH values were consistently higher than microelectrode pH measurements, indicating that the shell δ11B may reflect pH at a more localized site of calcification, rather than pH of the bulk EPF.

In Chapter 2, I investigate the effects of four different seawater pH levels (8.03, 7.93, 7.83, and 7.63) on seven complexes of temperate coralline algae collected from New Zealand. I examined the photophysiology, calcification, and geochemical proxies to probe the internal carbonate chemistry of seven different species of coralline algae under simulated end-of-century ocean acidification scenarios. Under ambient conditions we found clear physiological differences between branching and encrusting species. We found that OA treatments only had a significant effect on calcification of three of the seven species, Corallina berteroi, Corallina spp., and Jania “bottlebrush.” Additionally, OA only affected the calcification fluid pH (pHCF) of two species, decreasing pHCF for both Corallina beteroi and Jania “feather.” Nonetheless, for all species pHCF was constantly upregulated compared to seawater pH, indicating a strong control over calcifying fluid chemistry. My results underscore the high resilience of coralline algae calcification under the different end-of-century ocean acidification scenarios. This tolerance to OA is related to the species’ ability to maintain a stable carbonate chemistry to support calcification as seawater pH declined.

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Carbonate chemistry fitness landscapes inform diatom resilience to future perturbations

Published 22 September 2025 Science Closed
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Marine diatoms are an abundant and ecologically important phytoplankton group susceptible to changing environmental conditions. Currently available data assessing diatom responses focus on empirical comparisons between present-day and future conditions, rather than exploring the mechanisms driving these responses. Here, we conducted high-resolution growth experiments to map the fitness of diatoms across broad carbonate chemistry landscapes. Our results reveal species-specific carbonate chemistry niches, which can be used to predict ecological shifts between species under changing conditions driven by ocean acidification or ocean alkalinity enhancement. The results demonstrate that changes in diatom fitness are almost exclusively driven by carbon dioxide and proton concentrations, with bicarbonate exerting no discernible effect. Thus, current assumptions regarding the role of bicarbonate as a primary carbon source supporting diatom growth may be overestimated. This study presents a methodological and conceptual framework as a foundation for future studies to collate data capable of predicting species-specific responses and shifts in ecological niches driven by changes in marine carbonate chemistry.

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Opposing physiological performances of two coexisting gastropods to changing ocean climate

Published 18 September 2025 Science Closed
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The impact of climate change on the structure of ecological communities will be influenced by how different species respond to changing environmental conditions. In this study, we investigated the effects of increased temperature (summer Control, 21 °C; HT, 24 °C) and elevated CO2 levels (Control, 400 ppm; OA, 1000 ppm) on two species of co-occurring temperate gastropods – Turbo undulatus and Austrocochlea odontis. Biological responses to simulated future conditions were measured as growth rates (shell and tissue) and metabolic rates across thermal ramps (temperatures ranging from 15 °C to 38 °C) after 8 weeks of exposure. We found that T. undulatus exposed to HT, OA or HT × OA conditions had a higher metabolic rate throughout their thermal curve than control conditions. In addition, the temperature at which individuals had maximum metabolic rate (TMMR) was higher in animals acclimated to HT × OA than in other conditions, potentially demonstrating acclimation. In contrast, A. odontis showed antagonistic effects in response to OA and HT; metabolism was lowest under OA but highest under HT. Furthermore, TMMR was reduced in A. odontis exposed to HT and the combination of HT x OA. In terms of growth, T. undulatus exposed to HT and HT × OA grew three times more in shell length and ∼20-30% in weight compared to the control group or those exposed to only OA. In contrast, no treatment had a significant effect on growth in A. odontis. Overall, our findings suggest that the impact of ocean acidification and heating on metabolic function can differ between coexisting species, possibly depending on their evolutionary and life history strategies, and these differential responses could have significant implications for the structure of ecological communities.

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Transgenerational plasticity responses differ across genetically distinct families in the Sydney rock oyster, Saccostrea glomerata

Published 12 September 2025 Science Closed
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Across the globe, marine organisms need to rapidly respond to climate change. Acclimation through the mechanism of transgenerational plasticity (TGP) is now at the forefront of research, providing hope that some marine organisms may persist into the future. To date, however, because most studies have focussed on the average phenotypic species response to climate change, we do not know whether phenotypic responses vary among genotypes. Here, we take a next critical step in TGP research to assess whether TGP responses to ocean acidification (OA) differ among genotypes of the culturally significant and iconic Sydney Rock Oyster (SRO), Saccostrea glomerata. Adults of four genetically distinct families of the SRO were exposed to ambient (410 μatm) and elevated (1000 μatm) pCO2 for 9 weeks during reproductive conditioning. Following this exposure, we performed a within family cross of each family and measured the percentage development, abnormality, shell length and respiration rate of D-veliger larvae after 48 hours in the same ambient and elevated pCO2 treatments. We found significant variability in TGP responses among families to elevated pCO2, with positive, negative, and neutral responses in larval offspring. How well we understand the adaptive potential of oysters and their capacity to mount fast responses through TGP to climate change will determine our ability to ensure the sustainability of SRO populations, marine food security and the cultural heritage of this iconic species. Combined approaches quantifying both genetic and non-genetic TGP responses are needed to determine the total adaptive potential of other marine organisms to climate change.

Continue reading ‘Transgenerational plasticity responses differ across genetically distinct families in the Sydney rock oyster, Saccostrea glomerata’

Particulate inorganic carbon pools by coccolithophores in low-oxygen–low-pH waters off the Southeast Pacific margin

Published 10 September 2025 Science Closed
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A predicted consequence of ocean acidification is the decrease in coccolithophore-produced particulate inorganic carbon (PIC) pools. PIC is thought to enhance the sinking of particulate organic carbon (POC) to deeper waters, potentially influencing the depth of organic matter remineralization and subsurface O2 levels. To explore these potential feedbacks, we examined the relationships between PIC, coccolithophores, carbonate chemistry, and dissolved O2 in the Southeast Pacific open-ocean oxygen minimum zone – a region characterized by naturally low dissolved O2, low pH, and high pCO2 levels. Measurements of PIC and coccolithophore abundance from late spring 2015 and mid-summer 2018 revealed that coccolithophores, particularly Gephyrocapsa (Emiliania) huxleyi, were major contributors to PIC through the shedding of coccoliths. On average, about half of the PIC was attributed to reliably enumerated coccospheres and detached coccoliths, with significantly diminished pools below the euphotic zone. Temperature, O2, and pH emerged as key factors associated with PIC variability. PIC pools and PIC : POC ratios in both surface and subsurface waters in this naturally low-pH–low-O2 zone are lower than available data from most oceanic regions, with the exception of the Western Arctic. Our findings support the prediction that in upwelling regions with a shallow oxygen minimum zone, POC production is promoted by phytoplankton other than PIC-producing coccolithophores due to the injection of nutrient rich but low-pH water. This process decreases PIC : POC ratios, suggesting that the role of PIC in POC sedimentation might be decreased under such conditions. We emphasize that comparing PIC dynamics across diverse upwelling systems will be valuable for understanding how low-pH and low-O2 conditions influence POC fluxes mediated by coccolithophores.

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No effect of ocean acidification on individual-level variation in behaviour and susceptibility to predation in a Great Barrier Reef damselfish

Published 9 September 2025 Science Closed
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1) Ocean acidification, caused by rising carbon dioxide (CO2) in the atmosphere, has been reported to negatively impact a wide variety of behaviours in fishes, including activity, exploration, and predator avoidance.

2) These effects have been documented at the population level, but many animal species naturally show large and repeatable individual-level differences in behaviour. How environmental stressors, such as ocean acidification, affect behavioural variation at the individual level remains largely unknown but is critically important to understand adaptation given natural selection operates on variation at the individual rather than population level.

3) Using a statistical approach allowing variation in means and variation in variance to be modeled within a single framework, we quantified individual-level differences across five behaviours in the coral reef damselfish Pomacentrus amboinensis (emergence time, activity level, time spent sheltering, thigmotaxis, novel object inspection). We measured behaviour in a novel environment assay, twice before (CO2 ~450 µatm) and twice following acclimation to predicted end-of-century ocean acidification conditions (~1,100 µatm).

4) Following behavioural assays, we tested individual survival in a live predation experiment. We used predatory rock cod, Cephalopholis microprion, acclimated to the same CO2 treatments as Ambon damsel and examined predictors of survival probability.

5) All behaviours in damselfish were moderately and significantly repeatable, with no marked differences in repeatability estimates between the ambient CO2 and elevated CO2 treatment groups. Exposure to end-of-century ocean acidification conditions had no effect on any of the five behaviours measured, both in terms of group means and residual (within-individual) variance.

6) The probability of survival in the predation trials was similar for damselfish in the elevated and ambient CO2 treatment groups. Smaller damselfish as well as those that spent a greater amount of time inspecting a novel object (i.e., bolder individuals) had a lower probability of survival regardless of their CO2 treatment.

7) Our results challenge assumptions about the impacts of ocean acidification on coral reef fish behaviour and susceptibility to predation, both at the population and individual level. They also provide support for a trade-off between boldness and predation risk in fish.

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Projected cooling and pCO2 conditions in upwelling zones and their influence on a prominent rocky shore ecosystem engineer

Published 3 September 2025 Science Closed
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HIGHLIGHTS

  • End-of-century projections point to intensified OA and cooling in upwelling zones
  • Projected OA enhanced growth, calcification, and byssus production in P. purpuratus
  • However, projected cooling reversed OA effects on most of these biological traits
  • These findings highlight the relevance of cooling and its strong interaction with OA

ABSTRACT

By the end of the century, upwelling zones are expected to undergo distinct changes due to the accumulation of greenhouse gases in the atmosphere. These changes include an intensification of the winds causing upwelling, further reducing sea surface temperatures (cooling), and an intensification of ocean acidification (OA). While only a few studies have evaluated the influence of cooling conditions in these systems, even fewer have assessed the combined effects of cooling and projected OA. This study addressed this gap by exposing juveniles of the intertidal purple mussel (Perumytilus purpuratus), a prominent intertidal ecosystem engineer, to distinct temperatures and pCO2 levels. Using a mesocosm system and a 2×2 factorial design, groups of purple mussels were exposed to current (15°C) and projected cooling conditions (10°C), and current and projected pCO2 levels (500 and 1500 μatm, respectively). After two months, we quantified mussel growth, calcification, byssus thread production, clearance, and metabolic rates. Growth, calcification, and byssus thread production rates were consistently affected by temperature and by the interaction between temperature and pCO2: At current temperatures (15°C) all these variables increased in response to OA, but when exposed to projected cooling conditions (10°C), these trends reversed and declined with OA. Mussel clearance rates followed the same trend, but in this case the only significant factor was the interaction between variables. Meanwhile, metabolic rates declined with temperature. A close examination of the variation among treatments suggests that the main changes were consistently associated with a sharp decline in most response variables to a combination of cooling and high pCO2 conditions. Hence, projected end of the century cooling and OA are likely to have direct (negative) effects on this habitat-forming species. Indirectly, the combination of these stressors may weaken mussel bed structure and reduce habitat complexity, thereby halting the benefits provided to associated intertidal communities.

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Multidecadal decoupling between coral calcifying fluid and seawater saturation states

Published 1 September 2025 Science Closed
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Ocean acidification poses a threat to coral skeleton formation via reductions in the saturation state of aragonite (ΩAr) in seawater. Given that corals precipitate their skeletons from a calcifying fluid supplied by seawater, reductions in seawater ΩAr should, in theory, confound calcification. Here, we reconstruct up to 200 years of coral calcifying fluid ΩAr, using Raman spectroscopy techniques, at approximately monthly resolution in two Porites sp. skeletal cores from the Coral Sea region to investigate (i) the regulation of coral calcifying fluid ΩAr and (ii) the skeletal calcification response to industrial-era ocean acidification. Our results reveal a significant increase in calcifying fluid ΩAr, suggesting that some corals may adjust to the pace of acidification in the wild more effectively than suggested by short-term laboratory studies.

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Influence of intensified upwelling on two different Corallina officinalis Linneo 1758 populations by exploring direct and indirect effects

Published 26 August 2025 Science Closed
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In the perspective of a future ocean, climate change can alter upwelling systems globally. Along the Chilean coast, upwelling becomes intensified, leading to cool temperatures and low pH, which can affect common and widespread calcifying seaweed species such as Corallina officinalis. We measured physiological, biomineralogical, and palatability responses in two distinct populations originating from contrasting upwelling regimes, one from an upwelling area and the other from an upwelling shadow, by exposing them to current and future upwelling conditions. After 20 days of experimentation, photosynthetic responses such as maximum quantum yield (Fv/Fm) remained high (> 0.5) across populations. In contrast, maximal photosynthetic efficiency (rETRmax), light saturation point (Ek) and pigment content were higher in individuals exposed to future conditions, while alpha (electron transport efficiency) decreased over time. The carbonate content was higher in individuals exposed to future conditions, while the organic matter content differed between populations, with lower contents in the population originating from the site with higher environmental variability (-1.1%). Individuals exposed to future upwelling conditions presented higher soluble protein contents (2-3 mg/g wet weight) and were also more consumed by sea urchins (+162.7%). Our results indicate that the two C. officinalis populations possess strategies that confer tolerance to projected increases in upwelling, demonstrating their capacity to adapt to changing environmental conditions. However, rising herbivory pressure associated with intensified upwelling may exert a stronger influence on ecosystem dynamics, potentially altering future community composition.

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The influence of cross-generational warming on the juvenile development of a coral reef fish under ocean warming and acidification

Published 20 August 2025 Science Closed
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Marine ecosystems are facing escalating chronic and acute environmental stressors, yet our understanding of how multiple stressors influence individuals is limited. Here, we investigated how projected ocean warming (+1.5°C) during grandparental (F1) and parental (F2) generations of the spiny chromis damselfish (Acanthochromis polyacanthus), influences the sensitivity of F3 juveniles to ocean warming (present-day vs +1.5°C) and/or elevated CO2 (490 μatm vs 825 μatm). After 16 weeks of exposure, aerobic physiology (resting oxygen consumption, maximum oxygen consumption, and absolute aerobic scope), behaviour (boldness and activity), and growth (length and physical condition) were measured in F3 juveniles and the relationships between these performance traits was explored. We found that warming during F3 development resulted in juveniles that were shorter, bolder, and in better physical condition, while elevated CO2 resulted in shorter juveniles with a reduced resting oxygen consumption. However, across juvenile performance traits there was no interaction between ocean warming and acidification, demonstrating the additive nature of these two environmental stressors. Although we found limited signs of transgenerational plasticity, there was evidence of parental and grandparental carry-over effects which resulted in juveniles that were larger and/or in better condition when grandparents and parents experienced warming during their development regardless of the F3 juvenile developmental treatment. These finding illustrate the significant role phenotypic plasticity has on juvenile performance under projected future climate change.

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High-resolution monitoring of the pH under strong La Niña conditions in Gorgona Island, Colombian Pacific, Panama Bight

Published 18 August 2025 Science Closed
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Few studies have investigated the potential drivers of high-resolution (daily and 24-hour scales) on ocean acidification (OA) and the carbonate system in a coastal estuary during an intense La Niña event. Therefore, we conducted the first high-resolution total scale pH (pHT) monitoring every three hours for 56 days (13 September to 7 November 2021) at the Colombian Pacific in El Muelle reef, Gorgona National Natural Park. Two moored autonomous submersible instruments (iSAMI-pH and CTD-Diver) were deployed at a depth of 2 m in an area influenced by extreme precipitation, river discharge, semi-diurnal tides, and southwest winds during La Niña 2020-2023. Total alkalinity was derived from salinity data and used alongside pHT to calculate sea surface seawater partial pressure of CO2 (pCO2w; μatm), dissolved inorganic carbon (DIC; μmol kg-1), and omega aragonite saturation (Ωa). The findings suggest that the observed low pH (7.93) and aragonite saturation state (Ωa = 2.22) values are likely attributed to increased precipitation. This enhanced precipitation resulted in higher river discharge, transporting naturally low-pH water to the island via mixing mechanisms (RiOMar type 2). Daily, decreasing solar radiation may reduce the seawater temperature, simultaneously elevating the pCO2w levels and reducing pHT. In contrast, elevated precipitation may reduce surface seawater salinity through freshwater dilution. Throughout the diurnal cycle, peak pHT values were recorded during late afternoon hours, likely driven by photosynthetic activity, while minimum values coincided with early morning periods of maximal respiratory activity. These results underscore the dynamic nature of this area and emphasize the need for long-term evaluation.

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Ocean acidification threatens Niue’s coral reefs: a call for global action

Published 6 August 2025 Web sites and blogs Closed
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Ocean acidification, driven by anthropogenic carbon dioxide (CO₂) emissions, poses a severe threat to coral reef ecosystems worldwide, with significant implications for small island nations like Niue. This article examines the specific impacts of ocean acidification on Niue’s coral reefs, which are vital to the island’s biodiversity, economy, and cultural heritage. Through a situational analysis of Niue’s reefs and a review of global literature, the study highlights the chemical processes of acidification, its ecological consequences, and the socio-economic ramifications for Niue’s communities. The paper further explores the role of intergovernmental organizations and international treaties in addressing this crisis, emphasizing the need for coordinated global action. Recommendations are provided to mitigate acidification impacts through local conservation efforts, regional collaboration, and international policy advocacy. This article underscores the urgency of integrating ocean acidification into global climate agendas to protect vulnerable ecosystems like Niue’s coral reefs.

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Timing of calcification and environmental variability determine pH proxy fidelity in coastal calcifying macroalgae

Published 21 July 2025 Science Closed
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Long-lived calcifying marine biota are increasingly used as paleo-archives for reconstructing ocean pH. They enable exploration of the rate and magnitude of ocean acidification in shallow-water ecosystems serving as proxies for environmental pH reconstruction. However, shallow water systems often have highly variable carbonate chemistry, and the impact of this on the accuracy of pH reconstructions from long-lived marine calcifiers is not known. In particular, a better understanding of the timing of calcification with respect to environmental pH cyclicity is needed. To test the fidelity of coastal environmental pH proxies, we assessed the synchronicity between calcification and in situ diel carbonate chemistry in a tropical (One Tree Island, Great Barrier Reef, Australia) and a temperate (Loch Sween, Scotland) location using calcifying macroalgae (rhodolith-forming coralline algae) as a model system. Calcification occurred primarily during daylight hours, meaning a recording bias was introduced when compared to the full diel pH range (< 0.02 pH units). This bias resulted in pH offsets up to 0.043 pH units over the period 1860–2020, representing up to 34% of the projected pH change from 1860 in the tropics and up to 1.8% in temperate latitudes. Therefore, when proxy records are used to extend modern instrumental records of pH, we find that this may lead to bias, indicating daytime, nighttime, and full diel pH records should be assessed separately. We suggest that temporal pH cycles should be characterized at a local scale to enable incorporation of potential biases in the application of calcifying marine macroalgae to reconstruct pH change.

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Ocean acidification induces changes in circadian alternative splicing profiles in a coral reef fish

Published 14 July 2025 Science Closed
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Alternative splicing is a fundamental mechanism of gene expression regulation that increases mRNA diversity and can be partially regulated by the circadian clock. Time-dependent production of transcript isoforms from the same gene facilitates coordination of biological processes with the time of day and is a crucial mechanism enabling organisms to cope with environmental changes. In this study, we determined the impact of future ocean acidification conditions on circadian splicing patterns in the brain of fish, while accounting for diel CO2 fluctuations that naturally occur on coral reefs. The temporal splicing pattern observed across a 24-hour period in fish from the control group was largely absent in those exposed to either stable or fluctuating elevated CO2 conditions. Splicing patterns were influenced not only by an overall increase in CO2 concentration but also by its stability, with 6am and 6pm emerging as key timepoints when the majority of aberrant splicing events were identified. We found that fish in fluctuating CO2 conditions exhibited increased temporal plasticity in splicing events compared to fish in stable CO2 conditions. This was especially notable for genes associated with neural functioning. Our findings suggest that natural temporal splicing patterns in fish brains are disrupted by elevated CO2 exposure, with CO2 stability also influencing molecular responses. The increased plasticity in temporal splicing activity observed in fish in fluctuating CO2 environments may provide greater flexibility in biological responses to external pH changes, potentially enabling them to better cope with future ocean acidification conditions.

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Groundwater discharge found to alter coral reef ecosystems

Published 11 July 2025 Press releases Closed
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Groundwater directly affects water chemistry in coral reefs and triggers a cascade of changes in the coastal ecosystem, according to a new study led by University of Hawaiʻi at Mānoa oceanographers. The researchers describe the effect as a “Goldilocks scenario”—too much groundwater has a negative impact, and when the input is “just right,” the reef benefits.

Freshwater from land that flows into the ocean beneath the sea surface, termed submarine groundwater discharge, was found to increase nutrient availability, change acidity of the seawater, and impact the process by which corals build their skeletons. This research, published recently in Ecological Monographs, provides critical insights into the complex interactions between the land and ocean. 

“Submarine groundwater discharge is a widespread and underappreciated land–sea connection that delivers terrestrial nutrients and carbon to coastal ecosystems,” said Nyssa Silbiger, lead author of the study, associate director of the Uehiro Center for the Advancement of Oceanography, and associate professor in the Department of Oceanography at the UH Mānoa School of Ocean and Earth Science and Technology. “This profoundly influences coral reef health by triggering a cascade of chemical and biological changes that alter the cycling of carbon in these ecosystems.” 

The fundamental connection between land and sea through the flow of freshwater is a universal principle recognized as important for coastal health across all cultures. Porous volcanic islands throughout the tropics deliver much of this water through rivers and streams, but a major fraction emerges unseen directly into the coral reefs that ring these islands. This submarine groundwater discharge has long been recognized by Pacific peoples as important, with seeps frequently named and associated with specific communities of algae and fish relevant to subsistence. The new research has helped define the complex interplay of chemistry and biology that makes these inputs so important to the ecology of coral reefs. 

Continue reading ‘Groundwater discharge found to alter coral reef ecosystems’

Terrestrial nutrient inputs restructure coral reef dissolved carbon fluxes via direct and indirect effects

Published 11 July 2025 Science Closed
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The addition of terrestrial inputs to the ocean can have cascading impacts on coastal biogeochemistry by directly altering the water chemistry and indirectly changing ecosystem metabolism, which also influences water chemistry. Here, we use submarine groundwater discharge (SGD) as a model system to examine the direct geochemical and indirect biologically mediated effects of terrestrial nutrient subsidies on a fringing coral reef. We hypothesize that the addition of new solutes from SGD alters ecosystem metabolic processes including net ecosystem production and calcification, thereby changing the patterns of uptake and release of carbon by benthic organisms. SGD is a common land–sea connection that delivers terrestrially sourced nutrients, carbon dioxide, and organic matter to coastal ecosystems. Our research was conducted at two distinct coral reefs in Moʻorea, French Polynesia, characterized by contrasting flow regimes and SGD biogeochemistry. Using a Bayesian structural equation model, our research elucidates the direct geochemical and indirect biologically mediated effects of SGD on both dissolved organic and inorganic carbon pools. We reveal that SGD-derived nutrients enhance both net ecosystem production and respiration. Furthermore, the study demonstrates that SGD-induced alterations in net ecosystem production significantly influence pH dynamics, ultimately impacting net ecosystem calcification. Notably, the study underscores the context-dependent nature of these cascading direct and indirect effects resulting from SGD, with flow conditions and the composition of the terrestrial inputs playing pivotal roles. Our research provides valuable insights into the interplay between terrestrial inputs and coral reef ecosystems, advancing our understanding of coastal carbon cycling and the broader implications of allochthonous inputs on ecosystem functioning.

Continue reading ‘Terrestrial nutrient inputs restructure coral reef dissolved carbon fluxes via direct and indirect effects’

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