Coastal sediments are globally significant sources and sinks of greenhouse gases (GHGs), yet their contributions to climate feedbacks of warming and ocean acidification remain uncertain, in part due to limited understanding of short-term variability. Here, we use a fully factorial laboratory experiment to disentangle how diel light–dark and tidal inundation and exposure interact with warming and elevated pCO2 to regulate benthic fluxes of CO2, CH4, and N2O in estuarine sediments, alongside concurrent changes in benthic oxygen exchange. While warming and pCO2 exerted strong independent effects, their influence was shaped by diel and tidal fluctuations in redox conditions and oxygen availability, reflecting shifts in metabolic balance between primary production and respiration. Light consistently limited CO2, CH4, and N2O emissions through enhanced autotrophic uptake and oxygenation, while dark promoted anaerobic production pathways. N2O showed the greatest sensitivity to the combined effects of climate forcing and redox dynamics. Despite warming-driven stimulation of benthic heterotrophy and the production of all GHGs, CO2 remained the dominant greenhouse gas, with minimal CH4 and N2O fluxes due to the limited organic matter availability within the sediment. This reflects the strong redox controls on CH4 and N2O production, which relies on both oxygen depletion and organic substrate supply. Our findings emphasize that fine-scale temporal variability can significantly shape both the magnitude and climate sensitivity of benthic GHG emissions. Capturing these fine-scale controls is essential for accurately modeling the contributions of estuarine sediments to global GHG budgets and their feedbacks.
Continue reading ‘Light and tidal inundation and exposure regulate the sensitivity of estuarine benthic greenhouse gas fluxes to warming and ocean acidification’Posts Tagged 'primary production'
Light and tidal inundation and exposure regulate the sensitivity of estuarine benthic greenhouse gas fluxes to warming and ocean acidification
Published 28 April 2026 Science ClosedTags: biogeochemistry, biological response, Indian, laboratory, light, multiple factors, physiology, primary production, respiration, sediment
Eco-evolutionary dynamics of planktonic calcifying communities under ocean acidification
Published 12 March 2026 Science ClosedTags: adaptation, biological response, BRcommunity, calcification, communitymodeling, growth, modeling, mortality, otherprocess, performance, phytoplankton, primary production, zooplankton
Increasing emissions of CO2 into the atmosphere are causing ocean acidification, threatening calcifying organisms. In this study, we model the physiological responses of coccolithophorids to acidification to understand the ecological and evolutionary outcomes of a system in interaction with zooplankton. Assuming a trade-off between growth and protection against grazing, we show that calcification has bivalent effects on transfers between two trophic levels and that acidity can strongly alter energy transfers. Taking into account the evolution of calcifying phenotypes in response to acidification, we show that the system outcome contrasts with previous results. While the effect of evolution depends on how calcification affects grazing, it nevertheless follows that acidification leads to a decrease in calcifying capacity. This evolutionary decrease may be progressive, but can also lead to tipping points where abrupt shifts may occur. Such a counter-selection of calcification in turn affects ecosystem functioning, enhancing energy transfers within the system and modifying carbon fluxes. We discuss how such eco-evolutionary changes may impact food webs integrity, carbon sequestration into the deep ocean and therefore endanger the carbon pump stability.
Continue reading ‘Eco-evolutionary dynamics of planktonic calcifying communities under ocean acidification’Carbon concentration mechanisms in Canary Islands macroalgae and their implications for future benthic community structure under ocean acidification
Published 12 February 2026 Science ClosedTags: algae, biological response, BRcommunity, community composition, laboratory, North Atlantic, otherprocess, physiology, primary production, respiration, vents
In recent decades, due to the anthropogenic CO2 concentration increase in the atmosphere, the chemistry of seawater has been seriously altered, producing the phenomenon known as Ocean Acidification (OA). Of all the dissolved inorganic carbon (DIC) present in seawater, only 1% is in the form of CO2. However, if anthropogenic CO2 emissions to the atmosphere continue, it will no longer be a limiting resource. Part of the response of marine photosynthetic organisms to these changes depends on their carbon physiology. The presence and effectiveness of carbon concentration mechanisms (CCM) can define the production and growth of macroalgae under OA conditions. Although CCMs are not essential when the seawater concentration of inorganic carbon is high, species that do not use them can see their performance improved. Our goal was to determine the presence or absence of CCMs in a total of 19 species of common macroalgae in the Canary Islands through a pH drift experiment and to establish their primary production rates through incubations and measurements of the O2 variation. Samples of each species were incubated during 8, 24 and 32 h in isolated containers and under controlled lighting and temperature conditions. Of the 19 species studied, 11 presented CCM and 8 did not present CCM. Five of the eight species that did not show the presence of CCMs in the present study are present in the CO2 seeps of Fuencaliente and one of them, H. scoparia is a dominant species.
Continue reading ‘Carbon concentration mechanisms in Canary Islands macroalgae and their implications for future benthic community structure under ocean acidification’Summary of ocean acidification data collected by the National Coral Reef Monitoring Program in the U.S. Pacific Islands, 2021—2023
Published 10 February 2026 Newsletters and reports ClosedTags: biological response, BRcommunity, chemistry, corals, field, North Pacific, primary production
Coral reefs are among the most biologically diverse and economically valuable ecosystems on earth. They provide billions of dollars annually in food, jobs, recreation, coastal protection, and other critical ecosystem services (Brander & van Beukering, 2013; Costanza et al., 2014). However, these ecosystems are also among the most vulnerable to ocean acidification (OA). Even under the most optimistic model projections, increasing atmospheric and seawater carbon dioxide concentrations are likely to occur over the next few decades, decreasing seawater pH and reducing the availability of the carbonate ion (CO32-) building blocks that corals and other marine calcifiers use to construct reef habitat (Chan & Connolly, 2013; Jiang et al., 2023). OA threatens the persistence of coral reefs by reducing rates of coral and crustose coralline algae (CCA) calcification and accelerating rates of bioerosion, thereby lowering net production of calcium carbonate (CaCO3) and compromising the structural complexity and integrity of three-dimensional reef habitat (Cornwall et al., 2021; Hill & Hoogenboom, 2022). As a result, many of the ecological, economic, and cultural values offered by coral reefs could be significantly impacted by OA over the next century.
NOAA’s National Coral Reef Monitoring Program (NCRMP) provides a framework for long-term, national-level monitoring of the U.S.-affiliated coral reef areas. Funded jointly by the NOAA Coral Reef Conservation Program and Ocean Acidification Program, NCRMP assesses the status and trends of U.S. coral reef ecosystems and supports the management of the nation’s reefs (NOAA Coral Program, 2021). NCRMP’s long-term monitoring of OA and related coral reef ecosystem responses (NCRMP-OA) evaluates patterns and trends in carbonate chemistry and key ecosystem indicators across gradients of biogeography, oceanographic conditions, habitat types, and human impacts. These data sets are used to inform the efficacy of place-based coral reef management in close collaboration with federal, state, and jurisdictional partners.
To assess the progression of OA and impacts on coral reef ecosystems in the U.S. Pacific Islands, NCRMP-OA monitoring includes the following objectives:
- Conduct carbonate chemistry sampling to monitor spatial variability and temporal change in pH, aragonite saturation state (Ωar), and other carbon system parameters;
- Conduct diel carbonate chemistry water sampling and oceanographic instrument deployments at select sites;
- Conduct census-based carbonate budget assessments to estimate rates of coral reef biological carbonate production and erosion.
This report summarizes the monitoring effort and results from 2021–2023 NCRMP-OA sampling and surveys. Additional NCRMP environmental, benthic, and fish data are not included in this report, but they can be accessed at the links provided in the Data Availability section.
Continue reading ‘Summary of ocean acidification data collected by the National Coral Reef Monitoring Program in the U.S. Pacific Islands, 2021—2023’Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea
Published 5 December 2025 Science ClosedTags: biogeochemistry, biological response, community composition, laboratory, mesocosms, North Pacific, otherprocess, phytoplankton, primary production, respiration
Anthropogenic CO2 emissions and their continuous dissolution into seawater lead to seawater pCO2 rise and ocean acidification (OA). Phytoplankton groups are known to be differentially affected by carbonate chemistry changes associated with OA in different regions of contrasting physical and chemical features. To explore responses of phytoplankton to OA in the Chinese coastal waters, we conducted a mesocosm experiment in a eutrophic bay of the southern East China Sea under ambient (410 μatm, AC) and elevated (1000 μatm, HC) pCO2 levels. The HC stimulated phytoplankton growth and primary production during the initial nutrient-replete stage, while the community diversity and evenness were reduced during this stage due to the rapid nutrient consumption and diatom blooms, and the subsequent shift from diatoms to hetero-dinoflagellates led to a decline in primary production during the mid and later phases under nutrient depletion. Such suppression of diatom-to-dinoflagellate succession occurred with enhanced remineralization of organic matter under the HC conditions, with smaller phytoplankton becoming dominant for the sustained primary production. Our findings indicate that, the impacts of OA on phytoplankton diversity in the coastal water of the southern East China Sea depend on availability of nutrients, with primary productivity and biodiversity of phytoplankton reduced in the eutrophicated coastal water.
Continue reading ‘Ocean acidification alters phytoplankton diversity and community structure in the coastal water of the East China Sea’Sediment topography enhances the response of coral reef carbonate sediment dissolution to ocean acidification
Published 13 November 2025 Science ClosedTags: annelids, biological response, BRcommunity, calcification, chemistry, community composition, laboratory, mollusks, otherprocess, primary production, respiration, sediment
The interaction between water flow and sediment topography (e.g., surface ripples) in shallow, permeable coral reef carbonate sediments establishes pressure gradients that increase the rate of sediment–water solute exchange relative to water flow along a flat bottom. It is unknown how this effect from surface ripples may modify the rate at which the sediment porewater is exposed to future chemical changes in the overlying water column, such as elevated pCO2 that is causing ocean acidification (OA). To address this question, this study used a series of 22-h incubations in flume aquaria with live permeable calcium carbonate sediment communities and examined the interactive effect of pCO2 (400 and 1000 µatm) and surface topography (flat and rippled sediments) on invertebrate infaunal activity, carbonate sediment microbial metabolism, and inorganic carbonate dissolution. Results show that the introduction of oxygen into flat sediments was largely driven by infaunal activity, whereas introduction of oxygen into rippled sediments was largely driven by physical flow processes. Rippled sediments exhibited rates of respiration and gross primary production that were ~ 45% and ~ 50% higher, respectively, than flat sediments. An increase in pCO2 shifted the sediments in the flat flumes from net calcifying to net dissolving, an effect that was amplified an additional ~ 60% in rippled sediments. These results suggest that current estimates of coral reef carbonate sediment calcification may be underestimating the dissolution response to OA where the carbonate sediment environment exhibits ripples in the topography.
Continue reading ‘Sediment topography enhances the response of coral reef carbonate sediment dissolution to ocean acidification’Colony formation sustains the global competitiveness of N2-fixing Trichodesmium under ocean acidification
Published 10 November 2025 Science ClosedTags: biological response, growth, individualmodeling, modeling, nitrogen fixation, photosynthesis, primary production, prokaryotes
Anthropogenic CO2 emissions drive ocean acidification (OA). Trichodesmium, a key marine N2 fixer, displays contrasting growth responses to OA across morphotypes, with negative responses in free trichomes but neutral or positive in colonies. However, the lack of mechanistic understanding for these discrepancies has impaired our ability to predict the ecophysiological response of Trichodesmium in the changing ocean. Here, we developed ecophysiological models of Trichodesmium and underpin mechanisms behind contrasting responses to OA by distinct morphological adaptations. For free trichomes, our diurnal model corroborated previous findings that OA impairs nitrogenase efficiency and photosynthetic energy production. In colonies, however, OA alleviated copper and ammonia toxicity within the microenvironment, potentially with increased iron acquisition synergies, outweighing the minor effects of inorganic carbon limitation relief in the colony center. Projections suggest that globally, OA will reduce N2 fixation of trichomes by 16±6% but increase that of colonies by 19±24% within this century. By resolving morphotype-specific mechanisms, our study clarifies Trichodesmium’s adaptive strategies, which may enable it to sustain its competitiveness and biogeochemical impacts in the changing ocean.
Continue reading ‘Colony formation sustains the global competitiveness of N2-fixing Trichodesmium under ocean acidification’Microbe-host associations as drivers of benthic carbon and nitrogen cycling in a changing Mediterranean Sea
Published 14 April 2025 Science ClosedTags: biological response, BRcommunity, field, Mediterranean, nitrogen fixation, otherprocess, phanerogams, primary production, respiration, vents
Seagrasses, such as the endemic Mediterranean species Posidonia oceanica, are critical components of coastal marine ecosystems, providing essential ecosystem services, including carbon sequestration, nutrient cycling, and habitat formation. P. oceanica forms extensive meadows that serve as biodiversity hotspots and play a crucial role in mitigating climate change through long-term carbon storage. Despite their ecological significance, the interactions between P. oceanica and associated organisms, as well as their combined contributions to biogeochemical cycling, remain poorly understood, particularly under changing environmental conditions. This thesis explores the carbon and nitrogen cycling processes within the P. oceanica holobiont, focusing on the epiphytic and microbial communities, microbial driven metabolic processes, and the interaction between P. oceanica and larger associated invertebrates, such as the sponge Chondrilla nucula. Through field and laboratory experiments, this work demonstrates the significant role of epiphytic algae in the primary production of the seagrass holobiont, contributing a substantial portion of net primary production. Nitrogen cycling processes such as N₂ fixation, nitrification, and denitrification in the seagrass phyllosphere were quantified, revealing their importance in meeting the N demands of the seagrass holobiont, especially under natural ocean acidification conditions. Experiments near marine CO₂ vents indicated that ocean acidification accelerates net primary production and nitrogen cycling, while the structure of the microbial community associated with P. oceanica leaves remains largely stable. The facultative mutualism between P. oceanica and the sponge C. nucula further highlights the complexity of the seagrass holobiont. P. oceanica releases dissolved organic carbon, which meets a portion of the sponge’s respiratory carbon demand. Conversely, C. nucula releases dissolved inorganic nitrogen, including ammonium and nitrate generated by microbial nitrification, which supports seagrass growth. Stable isotope analysis suggests that the association facilitates nutrient exchange, with P. oceanica preferentially absorbing sponge-derived ammonium, while epiphytes may benefit from sponge-produced nitrate. This dynamic reduces seasonal fluctuations in productivity, stabilizing the seagrass ecosystem during periods of senescence. Sponge-associated nitrification contributes to the nitrogen budget of the seagrass holobiont, potentially reducing nutrient limitations in oligotrophic Mediterranean waters. The microbiome of C. nucula plays a key role in these processes, harboring nitrifiers that mediate the production of nitrate. High-throughput sequencing revealed taxonomic diversity among microbes associated with both the sponge and seagrass, including microorganisms involved in carbon and nitrogen cycling processes. These microbial communities not only mediate nutrient exchange within the seagrass-sponge association but also contribute to the overall resilience and productivity of the ecosystem. This thesis highlights the intricate interactions within the P. oceanica holobiont and its nested ecosystem with C. nucula. These findings underscore the importance of microbial and epiphytic communities in maintaining the resilience and productivity of seagrass meadows, particularly in nutrient-poor environments like the Mediterranean Sea. This research enhances our understanding of the biogeochemical processes that support seagrass ecosystem stability and provides valuable insights to guide conservation efforts in the face of climate change and anthropogenic pressures.
Continue reading ‘Microbe-host associations as drivers of benthic carbon and nitrogen cycling in a changing Mediterranean Sea’Eukaryotic phytoplankton drive a decrease in primary production in response to elevated CO2 in the tropical and subtropical oceans
Published 14 March 2025 Science ClosedTags: biological response, BRcommunity, community composition, field, North Pacific, phytoplankton, primary production
Significance
Marine phytoplankton, which contribute ~45% of global net primary production, are projected to be affected by ongoing ocean acidification (OA). However, the response of phytoplankton to acidification is not well constrained in ultraoligotrophic tropical and subtropical oceans where small (<20 µm) phytoplankton dominate. By conducting onboard microcosm experiments, we found community-level primary production decreased consistently following CO2 enrichment in the North Pacific Subtropical Gyre and northern South China Sea, while no significant changes were observed at the northernmost boundary of the subtropical gyre. Eukaryotic phytoplankton but not cyanobacteria were key drivers of these responses which occur primarily under nitrogen limitation. These findings enhance our understanding of OA impacts on phytoplankton and marine productivity in a changing climate.
Abstract
Ocean acidification caused by increasing anthropogenic CO2 is expected to impact marine phytoplankton productivity, yet the extent and even direction of these changes are not well constrained. Here, we investigate the responses of phytoplankton community composition and productivity to acidification across the western North Pacific. Consistent reductions in primary production were observed under acidified conditions in the North Pacific Subtropical Gyre and the northern South China Sea, whereas no significant changes were found at the northern boundary of the subtropical gyre. While prokaryotic phytoplankton showed little or positive responses to high CO2, small (<20 µm) eukaryotic phytoplankton which are primarily limited by low ambient nitrogen drove the observed decrease in community primary production. Extrapolating these results to global tropical and subtropical oceans predicts a potential decrease of about 5 Pg C y−1 in primary production in low Chl-a oligotrophic regions, which are anticipated to experience both acidification and stratification in the future.
Continue reading ‘Eukaryotic phytoplankton drive a decrease in primary production in response to elevated CO2 in the tropical and subtropical oceans’Ocean acidification and global warming may favor blue carbon service in a Cymodocea nodosa community by modifying carbon metabolism and dissolved organic carbon fluxes
Published 9 January 2025 Science ClosedTags: biogeochemistry, biological response, laboratory, mesocosms, morphology, multiple factors, North Atlantic, phanerogams, physiology, primary production, respiration, temperature
Highlights
- 45-days mesocosm experiment with whole-benthic community to mimic nature conditions
- Global warming (GW) and ocean acidification (OA) modify C dynamics on seagrasses.
- OA enhances GPP and NCP and synergistic effects when combined with GW.
- DOC production decreased with OA and GW separately, but increased when combined.
- Climate change potentially increases the blue carbon service of C. nodosa populations.
Abstract
Ocean acidification (OA) and global warming (GW) drive a variety of responses in seagrasses that may modify their carbon metabolism, including the dissolved organic carbon (DOC) fluxes and the organic carbon stocks in upper sediments. In a 45-day full-factorial mesocosm experiment simulating forecasted CO2 and temperature increase in a Cymodocea nodosa community, we found that net community production (NCP) was higher under OA conditions, particularly when combined with warming (i.e., synergistic effect). Moreover, under OA conditions, an increase in aboveground biomass and photosynthetic shoot area was recorded. Interestingly, DOC fluxes were reduced when exposed to OA; however, an increase occurred when both factors acted together (i.e., antagonistic effect), which was attributable to increased DOC release by plants. Our results suggest that C. nodosa populations in temperate latitude may favor blue carbon service in future scenarios of OA and GW by increasing the NCP, the DOC export with lower labile:recalcitrant ratio, and accumulating more organic carbon in upper sediments. These findings offer additional arguments for the urgent need to protect and conserve this valuable ecosystem.
Continue reading ‘Ocean acidification and global warming may favor blue carbon service in a Cymodocea nodosa community by modifying carbon metabolism and dissolved organic carbon fluxes’Symbiodiniaceae algal symbionts of Pocillopora damicornis larvae provide more carbon to their coral host under elevated levels of acidification and temperature
Published 25 November 2024 Science ClosedTags: biological response, BRcommunity, corals, laboratory, molecular biology, mortality, multiple factors, North Pacific, photosynthesis, physiology, primary production, protists, reproduction, respiration, temperature
Climate change destabilizes the symbiosis between corals and Symbiodiniaceae. The effects of ocean acidification and warming on critical aspects of coral survical such as symbiotic interactions (i.e., carbon and nitrogen assimilation and exchange) during the planula larval stage remain understudied. By combining physiological and stable isotope techniques, here we show that photosynthesis and carbon and nitrogen assimilation (H13CO3− and 15NH4+) in Pocillopora damicornis coral larvae is enhanced under acidification (1000 µatm) and elevated temperature (32 °C). Larvae maintain high survival and settlement rates under these treatment conditions with no observed decline in symbiont densities or signs of bleaching. Acidification and elevated temperature both enhance the net and gross photosynthesis of Symbiodiniaceae. This enhances light respiration and elevates C:N ratios within the holobiont. The increased carbon availability is primarily reflected in the 13C enrichment of the host, indicating a greater contribution of the algal symbionts to the host metabolism. We propose that this enhanced mutualistic symbiotic nutrient cycling may bolster coral larvae’s resistance to future ocean conditions. This research broadens our understanding of the early life stages of corals by emphasizing the significance of symbiotic interactions beyond those of adult corals.
Continue reading ‘Symbiodiniaceae algal symbionts of Pocillopora damicornis larvae provide more carbon to their coral host under elevated levels of acidification and temperature’The role of rolling corals and free-living calcifying coralline algae in the management of greenhouse gas CO2 in the Colombian Caribbean
Published 25 November 2024 Science ClosedTags: algae, biological response, BRcommunity, calcification, corals, dissolution, field, laboratory, mitigation, North Atlantic, photosynthesis, primary production, respiration
The ongoing increase in anthropogenic CO₂ emissions since the industrial revolution has accelerated ocean acidification (OA) by introducing CO₂ into seawater, forming carbonic acid and reducing pH levels. This acidification threatens marine calcifiers by weakening their capacity to build calcium carbonate structures and promoting the dissolution of existing skeletons. Nonetheless, calcifying organisms may contribute to mitigating OA effects. This study explores the roles of corals (rolling Siderastrea radians, a seagrass dweller) and free-living calcifying coralline algae (back reef) in CO₂ mitigation in seawater. Field experiments were conducted on Isla Grande (Corales del Rosario and San Bernardo National Natural Park, Colombian Caribbean), to observe the diel variations in photosynthesis and calcification of these uncommon reef builders across different times of the day. Results demonstrate diel shifts influenced by photosynthesis/respiration and calcification/dissolution, with free-living coralline algae exhibiting higher productivity and calcification rates than corals during the day. Notably, free-living coralline algae displayed pronounced hysteresis, reflecting high sensitivity to light. These findings underscore the significant role of free-living coralline algae in marine carbon cycling, suggesting a more substantial impact on CO₂ mitigation than previously recognized. Conserving free-living coralline algae and their habitats is thus critical for supporting marine ecosystem health and resilience amidst global change, warranting further research into their metabolic responses to inform conservation strategies.
Continue reading ‘The role of rolling corals and free-living calcifying coralline algae in the management of greenhouse gas CO2 in the Colombian Caribbean’The unique biogeochemical role of carbonate-associated organic matter in a subtropical seagrass meadow
Published 18 November 2024 Science ClosedTags: biogeochemistry, biological response, North Atlantic, phanerogams, primary production
The particulate organic matter buried in carbonate-rich seagrass ecosystems is an important blue carbon reservoir. While carbonate sediments are affected by alkalinity produced or consumed in seagrass-mediated biogeochemical processes, little is known about the corresponding impact on organic matter. A portion of particulate organic matter is carbonate-associated organic matter. Here, we explore its biogeochemistry in a carbonate seagrass meadow in central Florida Bay, USA. We couple inorganic stable isotope analyses (δ34S, δ18O) with a molecular characterization of dissolved and carbonate associated organic matter (21 tesla Fourier-transform ion cyclotron resonance mass spectrometry). We find that carbonate-associated molecular formulas are highly sulfurized compared to surface water dissolved organic matter, with multiple sulfurization pathways at play. Furthermore, 97% of the formula abundance of surface water dissolved organic matter is shared with carbonate-associated organic matter, indicating connectivity between these two pools. We estimate that 9.2% of the particulate organic matter is carbonate-associated, and readily exchangeable with the broader aquatic system as the sediment dissolves and reprecipitates.
Continue reading ‘The unique biogeochemical role of carbonate-associated organic matter in a subtropical seagrass meadow’Unraveling the influence of environmental variability and cryptic benthic assemblages on reef-scale primary production and calcification
Published 14 October 2024 Science ClosedTags: calcification, corals, North Pacific, physiology, primary production
Recovery of ecosystem function in the aftermath of climate extremes such as cyclones and marine heat waves occurs in contest of highly variable environmental conditions and more chronic disturbances such as ocean acidification, which can further alter community structure and function. The present study investigated short-term responses of reef-scale primary production (Net Ecosystem Production; NEP), calcification (Net Ecosystem Calcification; NEC) and community structure in 2018 and again five years later in 2022 on a coral reef flat in Lizard Island on Australia’s Great Barrier Reef, between and following multiple consecutive stressors, namely two cyclones (2014 and 2015) and back-to-back bleaching events (2016–2017 and 2020). NEC in 2022 was highly variable compared to what it was in 2018. Conversely, NEP was higher in 2022 even though light availability was often reduced by cloud cover. High variability in NEC indicated that environmental parameters may have immediate impacts on carbonate chemistry in seawater and may largely and quickly affect short-term recovery trajectories. Therefore, comparison of metabolic rates over short time scales across decades should be done with caution. We also found that cover of calcifiers and particularly algae were highest in coral rubble suggesting that typical benthic surveys in the open reef flat largely underestimate their abundance and possible contribution to NEP and NEC. This study adds to the evidence that NEC and NEP might not be exclusively related to coral cover and likely not tied to vertical reef accretion.
Continue reading ‘Unraveling the influence of environmental variability and cryptic benthic assemblages on reef-scale primary production and calcification’“Pink power”—the importance of coralline algal beds in the oceanic carbon cycle
Published 7 October 2024 Science ClosedTags: algae, biological response, calcification, primary production, South Atlantic
Current evidence suggests that macroalgal-dominated habitats are important contributors to the oceanic carbon cycle, though the role of those formed by calcifiers remains controversial. Globally distributed coralline algal beds, built by pink coloured rhodoliths and maerl, cover extensive coastal shelf areas of the planet, but scarce information on their productivity, net carbon flux dynamics and carbonate deposits hampers assessing their contribution to the overall oceanic carbon cycle. Here, our data, covering large bathymetrical (2–51 m) and geographical ranges (53°N–27°S), show that coralline algal beds are highly productive habitats that can express substantial carbon uptake rates (28–1347 g C m−2 day−1), which vary in function of light availability and species composition and exceed reported estimates for other major macroalgal habitats. This high productivity, together with their substantial carbonate deposits (0.4–38 kilotons), renders coralline algal beds as highly relevant contributors to the present and future oceanic carbon cycle.
Continue reading ‘“Pink power”—the importance of coralline algal beds in the oceanic carbon cycle’Carbon budgets of coral reef ecosystems in the South China Sea
Published 20 September 2024 Science ClosedTags: biological response, calcification, corals, North Pacific, primary production
The coral reef ecosystem is one of the most productive ecosystems in the ocean, and is also an important calcium carbonate deposition region. Because excess production is very low in coral reefs, organic carbon reservoirs are very limited. During the calcification process, each mole of CaCO3 will produce 1 mol of CO2, approximately 60% of which will be released into the atmosphere through the sea-air interface. This causes coral reefs to be large inorganic carbon reservoirs, but at the same time, most coral reefs act as atmospheric CO2 sources (which also act as sinks in some coral reefs). Therefore, clarifying the sea-air CO2 exchange flux and carbon storage is critical for understanding the carbon cycle in coral reef ecosystems. In this paper, we summarize the carbon cycle processes in the coral reefs of the South China Sea (SCS) and estimate the total CO2 budget and carbon reserves. According to current research, the coral reefs in this area act as a source of atmospheric CO2, releasing 0.37−1.59 × 1011 g C a-1 into the atmosphere. Owing to their extremely high biological productivity and carbonate productivity, the carbon reserves of coral reefs in the SCS range from 1.66–3.78 × 1012 g C a-1, which is an order of magnitude greater than the CO2 emissions at the sea–air interface. Overall, coral reefs in the SCS are important carbon storage areas. As the current results are still approximate, a more comprehensive and in-depth investigation is needed to clarify the carbon source/sink processes, regulatory mechanisms, and carbon storage capacity of SCS coral reefs.
Continue reading ‘Carbon budgets of coral reef ecosystems in the South China Sea’Drivers of seasonal to decadal mixed layer carbon cycle variability in subantarctic water in the Munida Time Series
Published 10 July 2024 Science ClosedTags: chemistry, methods, modeling, primary production, regionalmodeling, South Pacific
Using ancillary datasets and interpolation schemes, 20+ years of the Munida Time Series (MTS) observations were used to evaluate the seasonal to decadal variability in the regional carbon cycle off the southeast coast of New Zealand. The contributions of gas exchange, surface freshwater flux, physical transport processes and biological productivity to mixed layer carbon were diagnostically assessed using a mass-balanced surface ocean model. The seasonal and interannual variability in this region is dominated by horizontal advection of water with higher dissolved inorganic carbon (DIC) concentration primarily transported by the Southland Current, a unique feature in this western boundary current system. The large advection term is primarily balanced by net community production and calcium carbonate production, maintaining a net sink for atmospheric CO2 with a mean flux of 0.84±0.62 mol C m-2 y-1. However, surface layer pCO2 shows significant decadal variability, with the growth rate of 0.53±0.26 μatm yr-1 during 1998–2010 increasing to 2.24±0.47 μatm yr-1 during 2010–2019, driven by changes in advection and heat content. Changes in circulation have resulted in the regional sink for anthropogenic CO2 being 50% higher and pH 0.011±.003 higher than if there had been no long-term changes in circulation. Detrended cross-correlation analysis was used to evaluate correlations between the Southern Annular Mode, the Southern Oscillation Index and various regional DIC properties and physical oceanographic processes over frequencies corresponding the duration of the MTS. The drivers of variability in the regional carbon cycle and acidification rate indicate sensitivity of the region to climate change and associated impacts on the Southern Ocean and South Pacific.
Continue reading ‘Drivers of seasonal to decadal mixed layer carbon cycle variability in subantarctic water in the Munida Time Series’Rubble persistence under ocean acidification threatened by accelerated bioerosion and lower-density coral skeletons
Published 20 June 2024 Science ClosedTags: abundance, biological response, BRcommunity, calcification, chemistry, community composition, corals, dissolution, laboratory, morphology, North Atlantic, otherprocess, primary production, protists, respiration
As the balance between erosional and constructive processes on coral reefs tilts in favor of framework loss under human-induced local and global change, many reef habitats worldwide degrade and flatten. The resultant generation of coral rubble and the beds they form can have lasting effects on reef communities and structural complexity, threatening the continuity of reef ecological functions and the services they provide. To comprehensively capture changing framework processes and predict their evolution in the context of climate change, heavily colonized rubble fragments were exposed to ocean acidification (OA) conditions for 55 days. Controlled diurnal pH oscillations were incorporated in the treatments to account for the known impact of diel carbonate chemistry fluctuations on calcification and dissolution response to OA. Scenarios included contemporary pH (8.05 ± 0.025 diel fluctuation), elevated OA (7.90 ± 0.025), and high OA (7.70 ± 0.025). We used a multifaceted approach, combining chemical flux analyses, mass alteration measurements, and computed tomography scanning images to measure total and chemical bioerosion, as well as chemically driven secondary calcification. Rates of net carbonate loss measured in the contemporary conditions (1.36 kg m−2 year−1) were high compared to literature and increased in OA scenarios (elevated: 1.84 kg m−2 year−1 and high: 1.59 kg m−2 year−1). The acceleration of these rates was driven by enhanced chemical dissolution and reduced secondary calcification. Further analysis revealed that the extent of these changes was contingent on the density of the coral skeleton, in which the micro- and macroborer communities reside. Findings indicated that increased mechanical bioerosion rates occurred in rubble with lower skeletal density, which is of note considering that corals form lower-density skeletons under OA. These direct and indirect effects of OA on chemical and mechanical framework-altering processes will influence the permanence of this crucial habitat, carrying implications for biodiversity and reef ecosystem function.
Continue reading ‘Rubble persistence under ocean acidification threatened by accelerated bioerosion and lower-density coral skeletons’Impacts of climate change on the Ascension Island marine protected area and its ecosystem services
Published 8 May 2024 Science ClosedTags: chemistry, modeling, primary production, regionalmodeling
Abstract
This is the first projection of marine circulation and biogeochemistry for the Ascension Island Marine Protected Area (AIMPA). Marine Protected Areas are a key management tool used to safeguard biodiversity, but their efficacy is increasingly threatened by climate change. To assess an MPA’s vulnerability to climate change and predict biological responses, we must first project how the local marine environment will change. We present the projections of an ensemble from the Sixth Coupled Model Intercomparision Project. Relative to the recent past (2000–2010), the multi-model means of the mid-century (2040–2050) project that the AIMPA will become warmer (+0.9 to +1.2°C), more saline (+0.01 to +0.10), with a shallower mixed layer depth (−1.3 to −0.8 m), a weaker Atlantic Equatorial Undercurrent (AEU) (−1.5 to −0.4 Sv), more acidic (−0.10 to −0.07), with lower surface nutrient concentrations (−0.023 to −0.0141 mmol N m−3 and −0.013 to −0.009 mmol P m−3), less chlorophyll (−6 to −3 µg m−3) and less primary production (−0.31 to −0.20 mol m−2 yr−1). These changes are often more extreme in the scenarios with higher greenhouse gases emissions and more significant climate change. Using the multi-model mean for two scenarios in the years 2090–2100, we assessed how five key ecosystem services in both the shallow subtidal and the pelagic zone were likely to be impacted by climate change. Both low and high emission scenarios project significant changes to the AIMPA, and it is likely that the provision of several ecosystem services will be negatively impacted.
Plain Language Summary
Ascension Island is a small remote volcanic island in the equatorial Atlantic Ocean. The seas around Ascension Island have been protected from commercial fishing since 2019. We used the marine component of computer simulations of the Earth’s climate to try to understand the future of the Ascension Island Marine Protected Area (AIMPA). Over the next century, the AIMPA region will become warmer, more saline, more acidic, less productive, and with lower nutrient and chlorophyll concentrations in the surface waters. The most important current of the region, the Atlantic Equatorial Current, is also projected to weaken in all scenarios. These changes are likely to negatively impact the ability of the AIMPA to provide ecosystem services such as healthy ecosystems, fish stocks, the removal of carbon dioxide from the air, and attract tourism. This work is important because it is the first projection of the climate around the AIMPA since it was created, and it has allowed local policymakers to understand how the changing climate is likely to affect their environment and ecosystem services.
Key Points
- We present the first projection of the future marine circulation and biogeochemistry of the Ascension Island Marine Protected Area (AIMPA)
- The AIMPA will become warmer, more saline, more acidic, with less surface nutrients, primary production and chlorophyll
- The AIMPA’s capacity to provide ecosystem services will be significantly negatively impacted under a high emission scenario
Ocean acidification and food availability impacts on the metabolism and grazing in a cosmopolitan herbivorous protist Oxyrrhis marina
Published 8 March 2024 Science ClosedTags: abundance, biological response, growth, laboratory, multiple factors, North Pacific, nutrients, otherprocess, performance, physiology, primary production, protists, respiration, zooplankton
The heterotrophic dinoflagellate Oxyrrhis marina is an essential microzooplankton in coastal waters, linking the energy transfer from phytoplankton to higher trophic levels. It is of general significance to investigate how it responds and acclimates to ocean acidification (OA), especially under varied availabilities of food. Here, O. marina was exposed and acclimated to three pCO2 levels (LC: 415, MC:1000, HC:1500 μatm) for 60 days, and then was further grown under the CO2 levels with different levels of food (the microalgae Dunaliella salina) availability for about 8 generations. The OA treatments did not significantly hamper its growth and ingestion rates even under the reduced food availability and starvation (deprived of the microalgae), which significantly reduced its growth rate. While the impacts of OA on the growth and ingestion rates of O. marina were insignificant, the OA treatments appeared to have resulted in a faster decline of the heterotrophic dinoflagellate cells during the starvation period. Nevertheless, the acidic stress under the elevated pCO2 of 1000 or 1500 μatm decreased its respiration by about 53% or 59% with the high and by about 26% or 23% with the low food availability, respectively. Such OA-repressed respiration was also significant during the starvation period. On the other hand, the OA treatments and deprivation of the microalgae synergistically reduced the cellular quota of particulate organic C, N and P, resulting in a reduction of food value of the heterotrophic dinoflagellate as prey. In conclusion, our results show that O. marina is highly resilient to future ocean acidification by reducing its respiration and sustaining its ingestion of microalgae.
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