Soft-sediment habitats are crucial for marine coastal ecosystems, supporting diverse biodiversity both above and below the sediment. Ocean acidification, driven by rising CO2 and nutrient influx, enhances heterotrophic metabolism, raising CO2 levels and lowering pH. These alterations complicate the dynamics of tidal flat, emphasizing the need for further research into their impact on biodiversity. Within these ecosystems, deposit- and suspension-feeding bivalves play crucial roles. Tagelus dombeii, a bivalve mollusc found in soft sediments, exhibits burrowing behavior linked to food supply and is of significant commercial value in southern Chile. This study assessed the response capacity of T. dombeii to key stressors associated with global ocean change, such as ocean acidification and food availability. Our results revealed significant differences in pH levels between the water column and pore water from the sediment in experimental mesocosms. T. dombeii was affected by ocean acidification and food availability in terms of its morphological traits (i.e. length, width, height and growth rate), while oxygen consumption was influenced only by the interaction between acidification and food supply. Notably, heart rate remained constant but increased when food supply was low. Our study suggests that T. dombeii exhibits partial tolerance to variations in seawater pH and carbonate chemistry, possibly due to its natural exposure to acidic pore water, but it is sensitive to food availability. These plastic physiological responses suggest that T. dombeii may be less vulnerable to future global change scenarios, demonstrating potential resilience and ecological success in its natural habitat.
Continue reading ‘Infaunal bivalves exhibit resilience to ocean acidification but remain sensitive to food supply’Posts Tagged 'South Pacific'
Infaunal bivalves exhibit resilience to ocean acidification but remain sensitive to food supply
Published 26 June 2025 Science ClosedTags: biological response, chemistry, dissolution, laboratory, mesocosms, mollusks, morphology, multiple factors, physiology, South Pacific
Modeling terrestrial dissolved organic carbon and its effect on the carbonate system in the Sunda Shelf seas, Southeast Asia
Published 17 April 2025 Science ClosedTags: biogeochemistry, chemistry, modeling, North Pacific, regionalmodeling, South Pacific
Abstract
The flux of dissolved organic carbon (DOC) from land to sea is an important transfer within the global carbon cycle. The biogeochemical fate of this terrestrial DOC (tDOC) remains poorly understood and is usually neglected in ocean models. Southeast Asia accounts for around 10% of global tDOC flux, mostly from tropical peatland-draining rivers discharging onto the Sunda Shelf. We developed a new light-driven parameterization of tDOC remineralization that accounts for photochemical, microbial, and interactive photochemical–microbial degradation, and simulated the transport and remineralization of tDOC through the Sunda Shelf seas using the regional 3D hydrodynamical HAMSOM and biogeochemical ECOHAM models (only for the carbonate system). Our realistic hindcast simulations for 1958–2022 show that about 50% of riverine tDOC is remineralized before leaving the shelf. This lowers seawater pH across the entire inner Sunda Shelf by an average of 0.005 (by up to 0.05 in the Malacca Strait). Correspondingly, seawater pCO2 is raised, increasing yearly CO2 outgassing from the shelf by 19% (3.1 Tg C yr−1, 0.14 mol m−2 yr−1) during 2013–2022. Even regional ocean acidification trends increase, because river discharge and tDOC flux increase. Our model reveals large spatial variability with greatest inputs and remineralization of tDOC close to major peatlands, especially off Sumatra and Borneo. The interannual variability in tDOC input and the monsoonal current reversal lead to strong temporal variability in carbonate system parameters in these areas. Our results highlight the importance of representing tDOC in ocean models, and reveal the fate of tropical peatland tDOC.
Key Points
- We modeled terrestrial dissolved organic carbon (tDOC) using a new scheme for photo-, bio-, and interactive photo-bio-degradation
- TDOC input to the Sunda Shelf in 2013–2022 is 15.9 Tg C yr−1. 50% is remineralized on the shelf, 28% directly exported to Indian Ocean
- This drives shelf-wide outgassing of 3.1 Tg C yr−1 in 2013–2022, lowers pH and aragonite saturation, increases ocean acidification trends
Plain Language Summary
The transport of terrestrial dissolved organic carbon (tDOC) from land to sea via rivers is an important part within the global carbon cycle. The majority of this tDOC is remineralized by sunlight and marine bacteria, which produces CO2 leading to ocean acidification and CO2 outgassing into the atmosphere. The degradation process is poorly understood, usually neglected in ocean models. Southeast Asia accounts for around 10% of global tDOC flux, mostly from rivers with peatland areas in their catchment. We developed an equation of tDOC remineralization that depends on sunlight and accounts for photochemical, microbial, and interactive photochemical–microbial degradation. With this, we simulated the fate of tDOC using a 3D computer model system for the Southeast Asian region. Our realistic results for 1958–2022 show: 50% of the tDOC is remineralized before leaving the Sunda Shelf. As a result, the shelf water acidifies and emits more CO2 to the atmosphere. Because of increasing river freshwater runoff (from climate change), more tDOC is transported in time into the sea and more is remineralized, increasing the ocean acidification. This happens mostly in coastal seas close to rivers with much peatland in their catchment. This is harmful for calcifying marine organisms like corals.
Continue reading ‘Modeling terrestrial dissolved organic carbon and its effect on the carbonate system in the Sunda Shelf seas, Southeast Asia’Building ocean science capacity in the Solomon Islands: an ocean acidification training to empower local experts
Published 15 April 2025 Web sites and blogs ClosedTags: South Pacific
The Solomon Islands, consisting of more than 900 islands, are already suffering from the effects of climate change. The country faces rising sea levels (projected to increase by up to 89 cm by 2090 under high-emission scenarios) along with intensifying storms and coastal erosion. Between 1999 and 2018, the Solomon Islands ranked as the 65th most affected country by extreme weather events.
In addition to these threats, there is a hidden danger: the ocean is slowly becoming more acidic. This puts coral reefs and marine ecosystems at risk, vital for the local economy and providing food. Recent global models estimate that the pH in the southwest Pacific has decreased by 0.06 since preindustrial times. Leisz’s (2009) projections showed that by 2040, ocean acidification will begin to impact the areas around the Solomon Islands.
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In response to these growing threats, efforts are intensifying in the country to equip local scientists and institutions with the tools they need to monitor and adapt to ocean acidification. A recent five-day training held at the Solomon Islands National University (SINU) in Honiara marked a milestone in this journey.
Delivered by the Pacific Community, in partnership with The Ocean Foundation, the training brought together ocean experts from government, agencies and SINU. The training was led by Kim Currie and Miriama Vuiyasawa, experts in Ocean acidification at the Pacific Islands Ocean Acidification Centre (PIOAC), which SPC hosts.
The workshop aimed to improve participants’ skills and provide them with the latest tools to support ocean acidification research. They received practical training on how to use the “Global Ocean Acidification Observing Network in a Box kit,” a key toolkit that helps researchers and coastal communities collect and analyse ocean water samples for pH and total alkalinity, and to determine aragonite saturation.
Continue reading ‘Building ocean science capacity in the Solomon Islands: an ocean acidification training to empower local experts’Skeletal morphometrics suggests high fitness of hybrid coral recruits under ocean warming and acidification
Published 10 April 2025 Science ClosedTags: biological response, BRcommunity, corals, laboratory, morphology, multiple factors, South Pacific, temperature
Anthropogenic greenhouse gas emissions increase sea surface temperature and acidification, inhibiting calcification of reef-building corals. While ocean acidification is known to hinder skeletal development of newly settled coral recruits, little is known of its effects on older purebred or interspecific hybrid recruits, or its combined effects with temperature. Using 3D X-ray microscopy, we found that predicted mid-century ocean warming and acidification conditions (28 °C, 685 ppm pCO2) negatively affected the skeletal development of 7-month-old Acropora purebreds and hybrids in one direction (Acropora cf. kenti mother x Acropora loripes father). Conversely, the skeletal parameters of reciprocal hybrids (A. loripes mother x A. cf. kenti father) remained unaffected. Skeletal measurements taken from 3D data revealed patterns overlooked by previous 2D measurements, leading support to the likelihood of hybrid vigour in hybrids of A. loripes (mother) and A. cf. kenti (father) and the potential of interspecific hybridization as a reef restoration tool to enhance coral resilience.
Continue reading ‘Skeletal morphometrics suggests high fitness of hybrid coral recruits under ocean warming and acidification’Safeguarding South-East Asia’s marine ecosystems from ocean acidification threats
Published 28 March 2025 Newsletters and reports ClosedTags: Indian, policy, South Pacific
The increasing carbon dioxide emissions from human activities are being absorbed by the oceans, leading to a decrease in seawater pH levels worldwide. South-East Asia is particularly vulnerable to this problem, as the projected trend of ocean acidification severely threatens marine life in the region, as well as marine industry productivity and food safety. Urgent action must be taken by the Association of Southeast Asian Nations (ASEAN) Secretariat and its Member States to sustain coastal populations’ livelihoods and economic prosperity.
Recommendations:
- Improve marine protected areas (MPAs) by applying science-based design and grass-roots community participation
- Establish a regional task force and collaborative funding
- Increase public awareness and implement marine educational programmes through curriculum integration
Detrital source diversity moderates decomposition and nutrient release in current and future ocean conditions
Published 25 March 2025 Science ClosedTags: algae, biological response, BRcommunity, laboratory, multiple factors, South Pacific, temperature
Highlights
- The decomposition of mixed and single detrital sources was assessed in current and future ocean conditions.
- The identity of detrital sources significantly influenced decomposition rates, and carbon and nutrient release.
- Detrital mixing significantly decreased variation in mass loss and nitrogen release.
- Ocean warming sometimes increased rates of decomposition of macrophyte detritus.
- Ocean acidification did not significantly influence detrital mass loss or nutrient release.
Abstract
The complex interactions between detrital diversity and ocean climate change are not well understood. Here, we used sixteen outdoor raceways to test the hypothesis that ocean warming, and acidification would increase rates of decomposition and nutrient release from detritus of common macroalgae, but the magnitude of change would vary for single detrital sources compared to mixed sources. Our litter-bag experiment to test this hypothesis had six types of macroalgal detritus: (i) Ecklonia radiata, (ii) Sargassum vestitum, (iii) Caulerpa filiformis, (iv) Ecklonia and Sargassum mix, (v) Ecklonia and Caulerpa mix, and (vi) Sargassum and Caulerpa mix. The experimental design also had an orthogonal set of treatments testing effects of ocean warming and acidification, individually and combined, based on the RCP 8.5 climate model for 2081–2100. The identity of detrital sources significantly influenced decomposition rates, carbon liberation and nutrient release. The treatments with two detrital sources did not have increased rates of decomposition and nutrient release compared to single sources. However, detrital source mixing significantly moderated variation in decomposition and nutrient release rates. While ocean acidification had little effect on the decomposition of macroalgal detritus, ocean warming tended to increase rates of decomposition. Given that excessive decomposition can lead to severe anoxia, the results suggest the risk of this occurring will be greater in the warmer oceans of coming decades. In such circumstances, the moderating force of detrital diversity may become increasingly important in maintaining benthic oxygen concentrations and detritus-based production.
Continue reading ‘Detrital source diversity moderates decomposition and nutrient release in current and future ocean conditions’On the measurement of ocean acidity with ambient sound
Published 12 March 2025 Science ClosedTags: chemistry, field, methods, North Pacific, South Pacific
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 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. Measurements of the depth-dependent ambient noise field were carried out in the Philippine Sea, Mariana Trench, and Tonga Trench from 2009 to 2021. The wideband (5 Hz – 30 kHz) acoustic data were recorded with untethered, free-falling, autonomous instrument platforms known as Deep Sound, equipped with two or four hydrophones. In all the data collected, the power spectral slopes became steeper with depth due to the stronger attenuation of high frequencies compared to low frequencies. Depth-averaged pH values, ranging from 7.68 to 8.35, were obtained from eight instrument drops. The noise spectral method, which has the potential for determining the depth-averaged value of pH, with the averaging depth being adjustable, could be suitable for the long-term passive acoustic monitoring of ocean acidity.
Continue reading ‘On the measurement of ocean acidity with ambient sound’Spatiotemporal variability of seawater carbonate chemistry in diverse coral reef environments in South East Asia and Australia
Published 26 February 2025 Science ClosedTags: biogeochemistry, chemistry, field, modeling, regionalmodeling, South Pacific
Coral reefs are under threat from global environmental perturbations including ocean warming, acidification, and deoxygenation. The degree to which these perturbations will affect coral reefs is dependent on a range of factors including the local hydrodynamics and biogeochemical processes, both which vary widely across space and time. Consequently, not all coral reefs will be affected equally due to differences in local properties and processes. To develop predictive capacity for how coral reefs will be affected by ocean acidification (OA) it is necessary to first understand the current seawater CO2 chemistry variability and drivers. In this dissertation, autonomous sensors and discrete seawater samples were used to characterize the natural spatial and temporal variability of seawater CO2 chemistry across different reef scales and habitats in Australia and South East Asia (i.e., Heron Island, Great Barrier Reef; Dongsha Atoll and Taiping Island, South China Sea; and Onna-son Reef, Okinawa). In Heron Island, the largest spatial and temporal variability in seawater chemistry was associated with the most shallow, western region of the platform that also had the longest residence time. Interactions between reef geomorphology and timing of the tidal cycle greatly influenced chemical gradients and variability leading to some unexpected trends and patterns. On Dongsha, elevated pH and aragonite saturation state (ΩAr) were observed inside a semi-enclosed lagoon during both day and night. Future projections showed that this environment will not cross, detrimental aragonite thresholds (e.g., ΩAr < 2.92) as frequently as patch reefs and the large-scale lagoon of Dongsha. However, concurrent high water temperature and hypoxia indicated that this environment will not offer respite to taxa sensitive to OA. In Onna-son, the influence of seaweed cultivation on seawater chemistry during spring was compared to times of no cultivation during fall and winter. pH elevation was observed during both spring (+0.13 units) and fall (+0.10 units), but it was not possible to separate the role of cultivated seaweed from natural taxa. This dissertation demonstrates current coral reef seawater CO2 chemistry conditions and biochemical function, information that will be critical for making rigorous projections for the future.
Continue reading ‘Spatiotemporal variability of seawater carbonate chemistry in diverse coral reef environments in South East Asia and Australia’Conspecific interactions between corals mediate the effect of submarine groundwater discharge on coral physiology
Published 30 January 2025 Science ClosedTags: biological response, BRcommunity, chemistry, corals, field, photosynthesis, physiology, respiration, South Pacific
Land-based inputs, such as runoff, rivers, and submarine groundwater, can alter biologic processes on coral reefs. While the abiotic factors associated with land-based inputs have strong effects on corals, corals are also affected by biotic interactions, including other neighboring corals. The biologic responses of corals to changing environmental conditions and their neighbors are likely interactive; however, few studies address both biotic and abiotic interactions in concert. In a manipulative field experiment, we tested how the natural environmental gradient created by submarine groundwater discharge (SGD) affected holobiont and symbiont metabolic rates and endosymbiont physiology of Porites rus. We further tested how the effect of SGD on the coral was mediated by intra and interspecific interactions. SGD is a natural land-sea connection that delivers nutrients, inorganic carbon, and other solutes to coastal ecosystems worldwide. Our results show that a natural gradient of nutrient enrichment and pH variability as a result of acute SGD exposure generally benefited P. rus, increasing gross photosynthesis, respiration, endosymbiont densities, and chlorophyll a content. Conspecifics in direct contact with the a neighboring coral, however, altered the relationship between coral physiology and SGD, lowering the photosynthetic and respiration rates from expected values when the coral had no neighbor. We show that the response of corals to environmental change is dependent on the types of nearby neighbor corals and how neighbors alter the chemical or physical environment around the coral. Our study underscores the importance of considering biotic interactions when predicting the physiologic responses of corals to the environment.
Continue reading ‘Conspecific interactions between corals mediate the effect of submarine groundwater discharge on coral physiology’Uncertainties about the role of river and mangrove dissolved inorganic carbon and alkalinity loads in buffering the Great Barrier Reef lagoon
Published 13 January 2025 Science ClosedTags: chemistry, field, South Pacific
Terrestrial dissolved inorganic carbon (DIC) and total alkalinity (TAlk) loads have contrasting effects on the pH and carbonate chemistry of the coastal ocean. While TAlk can buffer against ocean acidification, elevated exports of free CO2 can further exacerbate ocean acidification. In this study, we quantify terrestrial DIC and TAlk loads from rivers and mangrove floodplains across six bioregions and varying flow conditions to assess their impact on the buffering capacity of the Great Barrier Reef (GBR) lagoon in Australia. For a mid-flow year, median terrestrial DIC and TAlk loads ranged from 0.72 to 0.89 Tg C yr−1 and 0.26 to 1.03 Tg C yr−1, respectively. We find that mangrove-dominated terrestrial inputs only have a small influence on the whole GBR but contribute 12.5% (range: 1.9%–45.7%) of the DIC and 18.7% (range: 2.8%–68.2%) of the TAlk inner shelf inventory. Depending on the approach used to estimate TAlk loads, mangroves have a potential short-term buffering effect on near-shore coastal waters due to higher TAlk loads. However, long-term mangrove TAlk production via pyrite formation complicates this interpretation, highlighting the need for ongoing monitoring to understand the complex interplay between terrestrial inputs and their effect on the GBR carbonate chemistry.
Key Points
- Current measurement uncertainties hinder our ability to accurately predict the effects of terrestrial inputs on the GBR coastal waters
- Mangrove floodplains dominate terrestrial dissolved inorganic carbon (DIC) and total alkalinity (TAlk) loads to the Great Barrier Reef (GBR) lagoon
- Terrestrial loads of DIC and TAlk are higher in high flow years and in tropical wet bioregions with localized effects on the GBR lagoon
Multi-variate hybrid modeling for pacific ocean acidification: predicting future pH trends and analyzing key biogeochemical drivers
Published 7 January 2025 Science ClosedTags: chemistry, modeling, North Pacific, regionalmodeling, South Pacific
Ocean acidification, driven by rising atmospheric carbon dioxide levels, poses a significant threat to the health of marine ecosystems, particularly in the Pacific Ocean. This study employs a multi-variate hybrid machine learning approach to predict future pH trends within the Pacific and to analyze the influence of key biogeochemical drivers on these trends. Hybrid models, strategically combining the strengths of individual algorithms, were developed for predicting several ocean acidification parameters. A performance analysis demonstrated the superior accuracy of hybrid models compared to their counterparts. The predicted pH trends reveal a concerning shift towards increased acidity within the Pacific Ocean, highlighting the urgency of understanding and mitigating its impacts. In-depth analysis was conducted to identify the relative influence of key biogeochemical factors on the changing pH dynamics. This research aims to provide crucial insights for developing targeted mitigation strategies and protecting the vulnerable ecosystems of the Pacific Ocean from the escalating consequences of ocean acidification.
Continue reading ‘Multi-variate hybrid modeling for pacific ocean acidification: predicting future pH trends and analyzing key biogeochemical drivers’Effects of pH, temperature, and light on the inorganic carbon uptake strategies in early life stages of Macrocystis pyrifera (Ochrophyta, Laminariales)
Published 1 January 2025 Science ClosedTags: algae, biological response, laboratory, light, multiple factors, physiology, South Pacific, temperature
The responses of seaweed species to increased CO2 and lowered pH (Ocean Acidification: OA) depend on their carbon concentrating mechanisms (CCMs) and inorganic carbon (Ci) preferences. However, few studies have described these mechanisms in the early life stages of seaweeds or assessed the effects of OA and its interactions with other environmental drivers on their functionality and photophysiology. Our study evaluated the effects of pH, light (PAR), temperature, and their interactions on the Ci uptake strategies and photophysiology in the early stages of Macrocystis pyrifera. Gametophytes were cultivated under varying pH (7.80 and 8.20), light (20 and 50 µmol photons m−2s−1), and temperature (12 and 16 °C) conditions for 25 days. We assessed photophysiological responses and CCMs (in particular, the extracellular dehydration of HCO3− to CO2 mediated by the enzyme carbonic anhydrase (CA) and direct HCO3− uptake via an anion exchange port). This study is the first to describe the Ci uptake strategies in gametophytes of M. pyrifera, demonstrating that their primary CCM is the extracellular conversion of HCO3− to CO2 mediated by CA. Additionally, our results indicate that decreased pH can positively affect their photosynthetic efficiency and maximum quantum yield; however, this response is dependent on the light and temperature conditions.
Continue reading ‘Effects of pH, temperature, and light on the inorganic carbon uptake strategies in early life stages of Macrocystis pyrifera (Ochrophyta, Laminariales)’Coexisting mangrove-coral habitats: trends in seawater chemistry and coral diversity
Published 20 December 2024 Science ClosedTags: biological response, BRcommunity, chemistry, corals, field, morphology, phanerogams, South Pacific
Coral reefs face unprecedented threats from climate change, with rising temperatures, ocean acidification, and other stressors endangering their survival. Coexisting mangrove-coral (CMC) habitats provide a natural laboratory to study coral resilience under extreme conditions. However, these habitats are rare and understudied, leaving gaps in understanding their biogeochemical and ecological dynamics. This thesis examines how mangrove proximity influences seawater chemistry, coral diversity, and morphology. A global review identified differences in seawater chemistry between habitat types and regions, driven by biogeochemical processes and freshwater inputs. Edge habitats, particularly in the Great Barrier Reef (GBR), were identified as understudied. An empirical study at Pioneer Bay, GBR, revealed significant spatial and temporal variations in seawater chemistry along a gradient from mangroves to open reefs. Corals near mangroves experienced greater fluctuations in pH, temperature, and oxygen, stabilizing with distance. Tidal flushing mitigated extremes, fostering coral resilience. Mangrove proximity significantly influenced benthic communities, coral morphology, and biodiversity. Extreme conditions near mangroves favored resilient corals like *Porites*, while intermediate sites supported the highest diversity due to nutrient influx and moderate disturbances. Farther sites were dominated by complex coral communities. Edge CMC habitats play a vital role in supporting coral adaptation to climate change. However, intensifying stressors threaten even resilient systems, underscoring the need for long-term monitoring and adaptive management to protect these critical biodiversity hotspots.
Continue reading ‘Coexisting mangrove-coral habitats: trends in seawater chemistry and coral diversity’Particulate inorganic carbon quotas by coccolithophores in low oxygen/low pH waters off the Southeast Pacific margin
Published 12 December 2024 Science ClosedTags: biogeochemistry, biological response, chemistry, community composition, field, otherprocess, phytoplankton, South Pacific
A predicted consequence of ocean acidification is its negative effect on the pools of Particulate Inorganic Carbon (PIC) that are essential for ‘ballasting’ the sinking of organic carbon, potentially leading to decreased subsurface oxygen. To explore such possible feedbacks, we investigated the relationships between PIC, coccolithophores, carbonate chemistry, and dissolved oxygen in the Southeast Pacific open ocean oxygen minimum zone, which naturally exhibits extremely low dissolved oxygen, low pH, and high pCO2 levels. Measurements of PIC and coccolithophore counts during late-spring 2015 and mid-summer 2018 revealed that coccolithophores, particularly Gephyrocapsa (Emiliania) huxleyi, significantly contributed to PIC through the shedding of coccoliths in the upper waters. On average, about a half of the PIC was attributed to countable coccoliths, with significantly diminished quotas observed below the euphotic depth. Temperature, oxygen, and pH were identified as key variables influencing PIC variation. PIC quotas were similar to those reported in other upwelling zones. However, PIC:POC ratios were substantially lower than what has been reported both in other open ocean and coastal margin areas, an effect that was more pronounced within the vertically defined oxygen minimum zone core. This study contributes to understanding the role of coccolithophores in PIC pools and suggests that the presence of low O2/low pH subsurface waters does not inhibit coccolithophore PIC quotas but may decrease the role of PIC in ballasting the export of organic carbon.
Continue reading ‘Particulate inorganic carbon quotas by coccolithophores in low oxygen/low pH waters off the Southeast Pacific margin’Extreme environmental variability induces frontloading of coral biomineralisation genes to maintain calcification under pCO2 variability
Published 6 December 2024 Science ClosedTags: adaptation, biological response, calcification, corals, field, laboratory, mesocosms, molecular biology, otherprocess, photosynthesis, physiology, South Pacific
Corals residing in habitats that experience high-frequency seawater pCO2 variability may possess an enhanced capacity to cope with ocean acidification, yet we lack a clear understanding of the molecular toolkit enabling acclimatisation to environmental extremes or how life-long exposure to pCO2 variability influences biomineralisation. Here, we examined the gene expression responses and micro-skeletal characteristics of Pocillopora damicornis originating from the reef flat and reef slope of Heron Island, southern Great Barrier Reef. The reef flat and reef slope had similar mean seawater pCO2, but the reef flat experienced twice the mean daily pCO2 amplitude (range of 797 v. 399 μatm day−1, respectively). A controlled mesocosm experiment was conducted over 8 weeks, exposing P. damicornis from the reef slope and reef flat to stable (218 ± 9) or variable (911 ± 31) diel pCO2 fluctuations (μatm; mean ± SE). At the end of the exposure, P. damicornis originating from the reef flat demonstrated frontloading of 25% of the expressed genes regardless of treatment conditions, suggesting constitutive upregulation. This included higher expression of critical biomineralisation-related genes such as carbonic anhydrases, skeletal organic matrix proteins, and bicarbonate transporters. The observed frontloading corresponded with a 40% increase of the fastest deposited areas of the skeleton in reef flat corals grown under non-native, stable pCO2 conditions compared to reef slope conspecifics, suggesting a compensatory response that stems from acclimatisation to environmental extremes and/or relief from stressful pCO2 fluctuations. Under escalating ocean warming and acidification, corals acclimated to environmental variability warrant focused investigation and represent ideal candidates for active interventions to build reef resilience while societies adopt strict policies to limit climate change.
Continue reading ‘Extreme environmental variability induces frontloading of coral biomineralisation genes to maintain calcification under pCO2 variability’Expanding cold-water coral reef knowledge towards deep-sea ecosystem management
Published 13 November 2024 Science ClosedTags: biological response, corals, physiology, South Pacific
The deep sea is our planet’s largest and least explored ecosystem. Once thought to be a barren abyss devoid of life, we have learned the deep sea is home to diverse ecosystems. One such deep-sea ecosystem that supports biodiversity is cold-water coral (CWC) reefs. Less studied than their tropical counterparts, CWC reefs provide a range of ecosystem services such as carbon storage, pharmaceutical development, and fisheries. Threats from climate change and increasing anthropogenic deep-sea activity make protecting and managing CWC reef futures exceptionally important. Scientific advances over the last decades have allowed us to better understand CWC reef ecosystems, though we remain far off from achieving effective ecosystem management. The overall aim of this thesis is to guide CWC reef management through expanding knowledge of these ecosystems. Despite the majority of CWC reef area being composed of dead framework, most research has focused on understanding live coral responses to climate change. Dead framework supports the highest levels of biodiversity in a CWC reef system and contributes significantly to carbon and nitrogen cycling. Live corals and dead coral skeletons are vulnerable to different environmental stressors. To understand reef composition and accurately predict their futures under climate change, the proportion of live coral colonies to the entire reef structure must be quantified. Chapter 2 of this thesis guides CWC reef management through increasing our knowledge of depth’s role in driving live and dead reef proportions. In Chapter 2, the live and dead proportions of CWC Solenosmilia variabilis reefs are quantified across four seamount features in the southwest Pacific Ocean. Images of CWC reefs are analysed with significant differences in the proportions of live coral between reefs at the Louisville Seamount Chain and Graveyard Seamount Complex. Depth is identified as a driver of live and dead reef proportions in these regions, with a larger proportion of live coral at shallow depths and dead intact framework at deeper depths. Additionally, the proportion of live coral in the Graveyard Seamount Complex remained stable between 2015 and 2020, despite significant differences in the surface areas of live coral, dead intact framework, and the reef. These results indicate reef proportions can be used to estimate the amount of dead intact framework threatened by the shallowing aragonite saturation horizon (ASH) due to ocean acidification at each site, which can help inform which sites could be protected as possible climate change refugia. Identifying depth as a driver of reef proportions quantifies reef health, identifies reef threats, and predicts reef impacts, all of which increases our knowledge of current and future reef conditions. Ocean acidification (OA) is a critical stressor and leads to dissolution of exposed calcium carbonate (CaCO3) in aragonite-undersaturated waters — a direct threat to dead CWC skeletons. This increased coral porosity from climate stressors threatens the structural integrity of the entire reef framework and could lead to a direct loss of habitat through crumbling. Laboratory studies have largely explored how skeletons grown under favourable conditions respond to exposure in OA conditions. We do not yet know if CWC skeletons grown in OA conditions are as robust as those grown in favourable conditions or if CWC skeletal structures are built differently in ideal and OA conditions. Chapter 3 of this thesis guides CWC reef management through increasing our knowledge of the 3-dimensional (3D) crystallographic structure of CWC. In Chapter 3, 3D volumes of CWC skeletal samples from above and below the ASH are compared using Electron Backscatter Diffraction (EBSD). Aragonite needles grow radially from Rapid Accretion Deposits (RAD) which join with neighbouring crystal structures to create the skeletal building blocks called sclerodermites. From large RADs, sequential imaging shows aragonite needles radiate with a preferred growth direction perpendicular to the calcification interface before rotating out of plane. Crystal size and orientation are compared between samples collected from above and below the ASH to understand differences in skeletal structure and better predict reef futures under OA. Neither aragonite crystal size or sclerodermite length were significantly different between the sample taken from below and above the ASH. Increasing our understanding of CWC 3D crystallographic structure above and below the ASH quantifies reef health, identifies reef threats, and predicts reef impacts, increasing our knowledge of current and future reef conditions. There are more CWC reefs in the world which have not yet been discovered, and thus cannot be managed. Therefore, increasing global capacity to carryout baseline deep-sea research is crucial to ensuring adequate protection and management for these vulnerable marine ecosystems. Limited at-sea training opportunities make it difficult to ensure the next generation of deep-sea scientists are properly trained in sea-going research methods. However, telepresence and remote learning can be used to increase the number of active participants on deep-sea expeditions. Chapter 4 of this thesis guides CWC reef management through increasing our knowledge of the effectiveness of virtual ship-to-shore training for increasing deep-sea capacity. Chapter 4 explores the 2021 iMirabilis2 expedition’s use of telepresence to virtually involve early career researchers from several countries in deep-sea science. Post expedition, a survey of onshore participants was conducted to assess and quantify the effectiveness of the peer-to-peer early career researcher ship-to-shore scheme. During the expedition, live, interactive training via WhatsApp and Zoom was accessed more than traditional static, unidirectional methods of blog posts and pre-recorded videos. All respondents either agreed or strongly agreed the scheme provided an inclusive and accessible platform to share deep-sea science. These results suggest similar schemes could be used to supplement shorter duration at-sea training or used prior to a seagoing experience to better prepare early career researchers, increasing inclusivity. Creating an inclusive and accessible platform to virtually share at-sea deep-sea science increases capacity for deep-sea exploration which can lead researchers to discover more CWC reefs. Through quantifying reef health, identifying reef threats, predicting reef impacts, and increasing capacity for deep-sea exploration, this thesis expands knowledge of CWC reef ecosystems to guide deep-sea ecosystem management.
Continue reading ‘Expanding cold-water coral reef knowledge towards deep-sea ecosystem management’Ocean warming, acidification, and chemistry of the South Pacific & North Atlantic: a brachiopod investigation
Published 25 October 2024 Science ClosedTags: mollusks, North Atlantic, South Pacific
Global CO2 emissions drive ocean warming and acidification. Local-level ocean data is limited, so natural archives like brachiopods are used to understand past oceanic conditions. Brachiopod shells record seawater temperatures, chemistry, and acidity. This thesis uses brachiopods from Paterson Inlet, New Zealand (1900–2021), and the Bay of Fundy, Canada (1970–2009) to track past oceanographic conditions and fill local data gaps. Global oceans recorded a decrease in δ13C DIC values of 0.50 ‰ (~1900-1985), comparable to the δ13CB value of -0.48‰ for Paterson Inlet (1900-2014), a rate of -0.04‰ per decade. The Bay of Fundy brachiopods recorded decreasing δ13CB values by 0.25‰ per decade (1970-2009). Ocean acidification is driven by the mixing of atmospheric CO2, and anthropogenic emissions are enriched in 12C, suggesting a link between pH and δ13CB values. The brachiopod shells δ18OB and Li/Ca levels record ambient seawater temperatures. In Paterson Inlet, seawater temperatures calculated with Li/Ca and δ18O values suggest cooling (ΔT = -0.035℃ per decade; 1900-2014). Temperatures calculated with δ18OB values for the Bay of Fundy indicate cooling (-0.25°C per decade; 1970-2009). Bay of Fundy seawater has recorded decreasing δ18OSW values by -0.16 ‰ per decade (1970-2022), reflecting potential arctic meltwater influx, cooling the seawater. The burning of coal drives CO2 emissions. Coal emissions contain various heavy metals, including selenium. Brachiopods record an increase in selenium concentrations of +6.14 mmol (1926-1960). Subsequently, in 1960-1980, selenium content decreased by -7.54 mmol but has since been increasing with a slightly upward trend of +1.78 mmol (2009-2021). Similar trends are observed in the brachiopod’s lanthanum content, another element found in coal, suggesting that brachiopod shell chemistry contains a record of coal burning. Archives such as brachiopods are an important source of information regarding the changing oceans. Although systems exist to monitor oceanic conditions, they cannot trace small-scaled effects. Brachiopods from Paterson Inlet and the Bay of Fundy record local changes in seawater conditions over the past 120 years. Some trends, such as δ13CB values, correspond with global ones, while others, such as temperatures, are not, reflecting the complex interaction of climate and weather/oceanographic changes on a local scale.
Continue reading ‘Ocean warming, acidification, and chemistry of the South Pacific & North Atlantic: a brachiopod investigation’Physiological resilience of intertidal chitons in a persistent upwelling coastal region
Published 13 September 2024 Science ClosedTags: biological response, calcification, field, mollusks, physiology, South Pacific
Current climate projections for mid-latitude regions globally indicate an intensification of wind-driven coastal upwelling due to warming conditions. The dynamics of mid-latitude coastal upwelling are marked by environmental variability across temporal scales, which affect key physiological processes in marine calcifying organisms and can impact their large-scale distribution patterns. In this context, marine invertebrates often exhibit phenotypic plasticity, enabling them to adapt to environmental change. In this study, we examined the physiological performance (i.e., metabolism, Thermal Performance Curves, and biomass and calcification rates) of individuals of the intertidal mollusk Chiton granosus, a chiton found from northern Peru to Cape Horn (5° to 55°S). Our spatial study design indicated a pattern of contrasting conditions among locations. The Talcaruca site, characterized by persistent upwelling and serving as a biogeographic break, exhibited lower pH and carbonate saturation states, along with higher pCO2, compared to the sites located to the north and south of this location (Huasco and Los Molles, respectively). In agreement with the spatial pattern in carbonate system parameters, long-term temperature records showed lower temperatures that changed faster over synoptic scales (1–15 days) at Talcaruca, in contrast to the more stable conditions at the sites outside the break. Physiological performance traits from individuals from the Talcaruca population exhibited higher values and more significant variability, along with significantly broader and greater warming tolerance than chitons from the Huasco and Los Molles populations. Moreover, marked changes in local abundance patterns over three years suggested population-level responses to the challenging environmental conditions at the biogeographic break. Thus, C. granosus from the Talcaruca upwelling zone represents a local population with wide tolerance ranges that may be capable of withstanding future upwelling intensification on the Southern Eastern Pacific coast and likely serving as a source of propagules for less adapted populations.
Continue reading ‘Physiological resilience of intertidal chitons in a persistent upwelling coastal region’Meta-analyses reveal climate change impacts on an ecologically and economically significant oyster in Australia
Published 13 August 2024 Science ClosedTags: biological response, fisheries, mollusks, review, socio-economy, South Pacific
Highlights
- Meta-analyses indicate significant ocean acidification (OA) and warming (OW) impacts
- OA and OW negatively impact the offspring size and mortality of Saccostrea glomerata
- Transgenerational plasticity (TGP) to OA positively benefits offspring size
- Research gaps include presence and persistence of TGP response to OA and OW
Abstract
Global oceans are warming and acidifying because of increasing greenhouse gas emissions which are anticipated to have cascading impacts on marine ecosystems and organisms, especially those essential for biodiversity and food security. Despite this concern, there remains some scepticism about the reproducibility and reliability of research done to predict future climate change impacts on marine organisms. Here we present meta-analyses of over two decades of research on the climate change impacts on an ecologically and economically valuable Sydney rock oyster, Saccostrea glomerata. We confirm with high confidence that ocean acidification (OA) has a significant impact on the size and mortality of offspring of S. glomerata, ocean warming (OW) impacts size and transgenerational exposure of adults to OA has positive benefits for offspring. These meta-analyses reveal gaps in understanding of OW and transgenerational plasticity on an ecologically and economically significant oyster species to ensure sustainability of this iconic oyster in Australia.
Continue reading ‘Meta-analyses reveal climate change impacts on an ecologically and economically significant oyster in Australia’
