The threat of ocean acidification: what you need to know (audio & video)

Published 30 March 2023 Presentations , Resources , Web sites and blogs Closed
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Ocean acidification is a topic that has been gaining more attention in recent years, and for good reason. It is a serious threat to the health and well-being of our oceans, and ultimately to the survival of countless species that call the ocean home.

In this video, we will explore what ocean acidification is, how it occurs, and the impacts it has on the environment. We will also discuss the primary drivers of ocean acidification, including the burning of fossil fuels and other human activities that release carbon dioxide into the atmosphere.

Through stunning visuals and clear explanations, we will delve into the science behind ocean acidification and why it is such a critical issue. We will also examine what steps can be taken to mitigate its effects and preserve the health of our oceans for future generations.

Whether you are a student, scientist, or concerned citizen, this video will provide a comprehensive overview of ocean acidification and its implications. Join us on this journey to understand one of the greatest challenges facing our planet today.

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A framework to evaluate preparedness for ocean acidification

Published 29 March 2023 Press releases Closed
How to prepare for ocean acidification, a framework

A vibrant coral reef in the Maldives. Credit: Luiz Rocha, California Academy of Sciences.

In a paper published today in the journal Environmental Research Letters, an international research team composed of scientists affiliated with more than a dozen institutions, including the California Academy of Sciences, propose a first-of-its-kind framework for governments around the world to evaluate their preparedness for—and guide future policies to address—ocean acidification, among the most dire threats to marine ecosystems.

“Ocean acidification is one of climate change’s silent killers,” says Rebecca Albright, Ph.D., Academy Curator of Invertebrate Zoology and founder of the Coral Regeneration Lab (CoRL). “While not as high-profile as threats like coral bleaching, ocean acidification will cause widespread destruction of marine environments by the end of this decade if we don’t take urgent action. To help policymakers identify what actions they should take, my collaborators and I asked ourselves, ‘What would a government have to do in order to have a comprehensive plan to safeguard both the environment and society from ocean acidification?'”

Ultimately, the researchers identified six aspects of effective ocean acidification policy, along with specific indicators for each, that policymaking bodies, from local governments to federal agencies, can use to evaluate and guide their own policies.

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Are we ready for ocean acidification? A framework for assessing and advancing policy readiness

Published 29 March 2023 Science Closed
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Effective climate policy that addresses carbon dioxide emissions is essential to minimizing and addressing the impacts of ocean acidification (OA). Here we present a framework to assess the readiness of OA policy, using coral reefs as a focal system. Six dimensions encompass comprehensive preparation by ecosystems and societies for the impacts of OA and other anthropogenic hazards: (1) climate protection measures, (2) OA literacy, (3) area-based management, (4) research and development, (5) adaptive capacity of dependent sectors, and (6) policy coherence. We define standardized indicators, identify leading countries, and evaluate the case study of Australia, the country with the largest coral reef system. The framework provides a rubric for a government unit to self- assess strengths and weaknesses in policy preparedness and to prioritize future endeavors.

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Projected increase in carbon dioxide drawdown and acidification in large estuaries under climate change

Published 28 March 2023 Science Closed
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Most estuaries are substantial sources of carbon dioxide (CO2) to the atmosphere. The estimated estuarine CO2 degassing is about 17% of the total oceanic uptake, but the effect of rising atmospheric CO2 on estuarine carbon balance remains unclear. Here we use 3D hydrodynamic-biogeochemical models of a large eutrophic estuary and a box model of two generic, but contrasting estuaries to generalize how climate change affects estuarine carbonate chemistry and CO2 fluxes. We found that small estuaries with short flushing times remain a CO2 source to the atmosphere, but large estuaries with long flushing times may become a greater carbon sink and acidify. In particular, climate downscaling projections for Chesapeake Bay in the mid-21st century showed a near-doubling of CO2 uptake, a pH decline of 0.1–0.3, and >90% expansion of the acidic volume. Our findings suggest that large eutrophic estuaries will become carbon sinks and suffer from accelerated acidification in a changing climate.

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The clam before the storm: a meta analysis showing the effect of combined climate change stressors on bivalves

Published 28 March 2023 Science Closed
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Impacts of a range of climate change on marine organisms have been analysed in laboratory and experimental studies. The use of different taxonomic groupings, and assessment of different processes, though, makes identifying overall trends challenging, and may mask phylogenetically different responses. Bivalve molluscs are an ecologically and economically important data-rich clade, allowing for assessment of individual vulnerability and across developmental stages. We use meta-analysis of 203 unique experimental setups to examine how bivalve growth rates respond to increased water temperature, acidity, deoxygenation, changes to salinity, and combinations of these drivers. Results show that anthropogenic climate change will affect different families of bivalves disproportionally but almost unanimously negatively. Almost all drivers and their combinations have significant negative effects on growth. Combined deoxygenation, acidification, and temperature shows the largest negative effect size. Eggs/larval bivalves are more vulnerable overall than either juveniles or adults. Infaunal taxa, including Tellinidae and Veneridae, appear more resistant to warming and oxygen reduction than epifaunal or free-swimming taxa but this assessment is based on a small number of datapoints. The current focus of experimental set-ups on commercially important taxa and families within a small range of habitats creates gaps in understanding of global impacts on these economically important foundation organisms.

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The influence of ocean acidification and warming on responses of Scylla serrata to oil pollution: an integrated biomarker approach

Published 28 March 2023 Science Closed
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Graphical abstract

Highlights

  • The OAW conditions reduce tolerance capacity of crabs to acute pollution stress.
  • A greater degree of stress was experienced in oil exposure under OAW conditions.
  • Augmented antioxidant and detoxification enzyme activity was noted.

Abstract

Anthropogenic activities primarily combustion of fossil fuel is the prime cause behind the increased concentration of CO2 into the atmosphere. As a consequence, marine environments are anticipated to experience shift towards lower pH and elevated temperatures. Moreover, since the industrial revolution the growing demand for petroleum-based products has been mounting up worldwide leading to severe oil pollution. Sundarbans estuarine system (SES) is experiencing ocean warming, acidification as well as oil pollution from the last couple of decades. Scylla serrata is one of the most commercially significant species for aquaculture in coastal areas of Sundarbans. Thus, the prime objective of this study is to delineate whether exposure under ocean warming and acidification exacerbates effect of oil spill on oxidative stress of an estuarine crab S. serrata. Animals were separately exposed under current and projected climate change scenario for 30 days. After this half animals of each treatment were exposed to oil spill conditions for 24 h. Oxidative stress status superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), lipid peroxidation (LPO level) and DNA damage (Comet assay) were measured. Augmented antioxidant and detoxification enzyme activity was noted except for SOD but failed to counteract LPO and DNA damage. The present results clearly highlighted the detrimental combined effect of OWA and pollution on oxidative stress status of crabs that might potentially reduce its population and affect the coastal aquaculture in impending years.

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Reef monitoring structure installed at Pulau Gaya

Published 28 March 2023 Media coverage , Web sites and blogs Closed
Edwin (second from left) presenting the award to Gillian.

 The Marine Ecology Research Centre (MERC) at Pulau Gaya completed installing and commissioning Autonomous Reef Monitoring Structure (ARMS) and Calcification Accretion Units (CAUs) on February 2.

The successful deployment was led by Professor Dato’ Dr Aileen Tan, director of the Centre for Marine and Coastal Studies (CEMACS), Universiti Sains Malaysia, Penang.

“This is the first step in a research collaboration between MERC and the Intergovernmental Oceanographic Commission (IOC) of UNESCO, following the protocol established by National Oceanic and Atmospheric Administration (NOAA),” said MERC’s project director Alvin Wong in a statement issued in conjunction with the award from the Malaysia Book of Records for the MERC – The First Ocean Acidification Monitoring Station for South China Sea held at Le Meridien on Monday.

The award was presented to ECHO Resorts owner, Gillian Tan by The Malaysia Book of Records Senior Record Consultant, Edwin Yeoh.

He added that this was also an effort to achieve the Sustainable Development Goal 14: Life below water.

“The research under the title ‘Research and Monitoring of the Ecological Impacts of Ocean Acidification on Coral Reef Ecosystems’ would improve the understanding of ocean acidification and the potential damaging effects of ocean acidification on marine resources and ecosystems,” he said.

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Effects of ocean acidification and warming on the specific dynamic action of California Grunion (Leuresthes tenuis) larvae

Published 27 March 2023 Science Closed
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Highlights

  • SDA was measured as the difference in metabolic rate of fed and non-fed fish.
  • SDA is ∼15% of the daily metabolic energy costs for California Grunion larvae.
  • OA conditions shifted the SDA response earlier.
  • Changes in SDA with climate can have downstream effects on larval growth.

Abstract

Ocean acidification (OA) and Ocean Warming (OW) are ongoing environmental changes that present a suite of physiological challenges to marine organisms. Larval stages may be especially sensitive to the effects of climate change because the larval phase is a time of critical growth and development. Of particular importance to growth is Specific Dynamic Action (SDA) – the energy used in digestion, absorption, and assimilation of food. Relatively little is known about the energetics of SDA for larval fishes and even less is known about how SDA may be affected by climate change. In this study we used feeding experiments and respirometry assays to characterize the functional form of SDA for California Grunion (Leuresthes tenuis). In a second set of experiments, we tested the independent and combined effects of ocean acidification and warming on SDA. Our first experiment revealed that an elevated metabolic rate was detectable within an hour of feeding, peaked at 3–6 h post feeding, and lasted about 24 h in total. Experiments testing the effects of acidification and warming revealed that temperature generally increased the maximum rate of postprandial respiration and the total amount of energy expended via SDA. In an experiment where feeding level was the same for fish held at different temperatures, elevated pCO2 increased the maximum rate of postprandial respiration and shortened the SDA response. However, in an experiment that allowed fish to consume more food at high temperatures, effects of pCO2 on SDA were minimal. The effects of OA on SDA may depend on a combination of temperature and food availability, and the disruption of SDA with OA may be part of a chain of events where digestion and assimilation efficiency are impaired with potential consequences for growth, survival, and population replenishment.

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Field development of Posidonia oceanica seedlings changes under predicted acidification conditions

Published 27 March 2023 Science Closed
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Ocean acidification has been consistently evidenced to have profound and lasting impacts on marine species. Observations have shown seagrasses to be highly susceptible to future increased pCO2 conditions, but the responses of early life stages as seedlings are poorly understood. This study aimed at evaluating how projected Mediterranean Sea acidification affects the survival, morphological and biochemical development of Posidonia oceanica seedlings through a long-term field experiment along a natural low pH gradient. Future ocean conditions seem to constrain the morphological development of seedlings. However, high pCO2 exposures caused an initial increase in the degree of saturation of fatty acids in leaves and then improved the fatty acid adjustment increasing unsaturation levels in leaves (but not in seeds), suggesting a nutritional compound translocation. Results also suggested a P. oceanica structural components remodelling which may counteract the effects of ocean acidification but would not enhance seagrass seedling productivity.

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OrgAlkCalc: estimation of organic alkalinity quantities and acid-base properties with proof of concept in Dublin Bay

Published 27 March 2023 Science Closed
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Highlights

  • Global Ocean Acidification Observing Network TA titration apparatus can be modified to perform organic alkalinity titrations.
  • Open-source software can be used to estimate the concentrations and acid-base properties of organic alkalinity.
  • Organic alkalinity poses a significant fraction of TA in Dublin Bay.

Abstract

The presence and influence of organic species is generally omitted in total alkalinity (TA) analysis. This has direct implications to calculated carbonate system parameters and to key descriptors of ocean acidification, especially in coastal waters where organic alkalinity (OrgAlk) can contribute significantly to TA. As titratable charge groups of OrgAlk can act as unknown seawater acid-base systems, the inclusion of the total concentration and apparent dissociation constants of OrgAlk in carbonate calculations involving TA is required to minimise uncertainty in computed speciation. Here we present OrgAlkCalc, an open-source Python based programme that can be used in conjunction with simply modified Global Ocean Acidification Observing Network (GOA-ON) TA titration apparatus to measure TA and OrgAlk, as well as return estimations of associated acid-base properties. The modified titration apparatus and OrgAlkCalc were tested using samples collected from the transitional waters of Dublin Bay, Ireland over a 8 month period (n = 100). TA values ranged from 2257 to 4692 μmol·kg−1 and indicated that freshwater inputs pose a significant source of carbonate alkalinity to Dublin Bay. OrgAlk values ranged from 46 to 234 μmol·kg−1 and were generally observed to be higher in more saline waters, with elevated levels in the Autumn/Winter period. The dissociation constants of two distinct OrgAlk charge groups were identified, with pK values in agreement with previously reported values for humic substances. The majority of OrgAlk charge group concentrations were associated with carboxyl-like charge groups.

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UBC gene family and their potential functions on the cellular homeostasis under the elevated pCO2 stress in the diatom Phaeodactylum tricornutum

Published 24 March 2023 Science Closed
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Graphical abstract

Highlights

  • 18 PtUBCs were identified into 5 independent clades.
  • Cis-acting elements related to stress responses were characterized from PtUBCs.
  • PtUBC15, PtUBC16 and PtUBC7 might have a negative effect during the ERAD pathway.
  • The misfolded/ unfolded proteins might be degraded by the ERAD mechanism.

Abstract

Ocean acidification (OA) as a result of more and more anthropogenic CO2 release, has already been referred to a severe ecological environmental issue. OA would destroy the balance of ocean carbonate buffering system and have negative effects on marine primary producers. Diatom Phaeodactylum tricornutum is one of the most important primary producers in the ocean, and it is susceptible to the elevated pCO2 stress. Under the elevated pCO2 stress, endoplasmic reticulum-associated degradation (ERAD) and its important components Ubiquitin-conjugating enzymes (UBCs) are pivotal to sustain cellular homeostasis. However, systematic investigation regarding phylogenetic relationships of UBC gene family, expression profiles under the elevated pCO2 stress and their potential functions on the cellular homeostasis of P. tricornutum remain poorly understood. In this study, a genome-wide analysis of PtUBC gene family was performed. It was shown that 18 PtUBC genes were unevenly distributed to the 14 chromosomes of total 33 chromosomes in P. tricornutum. Phylogenetic analysis showed that 18 PtUBC proteins were divided into 5 groups and each of them contained different conserved motifs. Besides, lots of cis-acting elements related to diverse stress responses were identified from PtUBC genes. Remarkably, transcriptomic analysis revealed that 3 PtUBC genes (PtUBC15, PtUBC16 and PtUBC7) were downregulated under the exposure to elevated pCO2 level, while the other 15 PtUBC genes did not have significant expression. Meanwhile, the model of endoplasmic reticulum-associated degradation (ERAD) mechanism was displayed, explaining that the misfolded/ unfolded proteins under the elevated pCO2 stress would be accumulated and then degraded via the ERAD mechanism to sustain the cellular homeostasis. The downregulated PtUBC genes might have a negative effect on the ERAD mechanism. Overall, this study provided an important foundation for further understanding of possible functions of PtUBC genes, especially on the cellular homeostasis, and the regulatory mechanism of PtUBCs on the diatom response to different environmental stresses.

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Assessing synergies and trade-offs of diverging Paris-compliant mitigation strategies with long-term SDG objectives

Published 24 March 2023 Science Closed
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Highlights

  • The Paris Agreement and the Sustainable Development Goals (SDGs) are interlinked.
  • Mitigation strategies chosen will affect how SDGs interact.
  • Technological and nature-based mitigation pathways increase resource consumption.
  • Mitigation strategies relying on behavioural changes limit potential SDG trade-offs.
  • Anticipating interdependences supports the design of SDG and Paris-compatible policies.

Abstract

The Sustainable Development Goals (SDGs) and the Paris Agreement are the two transformative agendas, which set the benchmarks for nations to address urgent social, economic and environmental challenges. Aside from setting long-term goals, the pathways followed by nations will involve a series of synergies and trade-offs both between and within these agendas. Since it will not be possible to optimise across the 17 SDGs while simultaneously transitioning to low-carbon societies, it will be necessary to implement policies to address the most critical aspects of the agendas and understand the implications for the other dimensions. Here, we rely on a modelling exercise to analyse the long-term implications of a variety of Paris-compliant mitigation strategies suggested in the recent scientific literature on multiple dimensions of the SDG Agenda. The strategies included rely on technological solutions such as renewable energy deployment or carbon capture and storage, nature-based solutions such as afforestation and behavioural changes in the demand side. Results for a selection of energy-environment SDGs suggest that some mitigation pathways could have negative implications on food and water prices, forest cover and increase pressure on water resources depending on the strategy followed, while renewable energy shares, household energy costs, ambient air pollution and yield impacts could be improved simultaneously while reducing greenhouse gas emissions. Overall, results indicate that promoting changes in the demand side could be beneficial to limit potential trade-offs.

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Sensitivity of fishery resources to climate change in the warm-temperate Southwest Atlantic Ocean

Published 24 March 2023 Science Closed
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Climate change impacts on fishery resources have been widely reported worldwide. Nevertheless, a knowledge gap remains for the warm-temperate Southwest Atlantic Ocean—a global warming hotspot that sustains important industrial and small-scale fisheries. By combining a trait-based framework and long-term landing records, we assessed species’ sensitivity to climate change and potential changes in the distribution of important fishery resources (n = 28; i.e., bony fishes, chondrichthyans, crustaceans, and mollusks) in Southern Brazil, Uruguay, and the northern shelf of Argentina. Most species showed moderate or high sensitivity, with mollusks (e.g., sedentary bivalves and snails) being the group with the highest sensitivity, followed by chondrichthyans. Bony fishes showed low and moderate sensitivities, while crustacean sensitivities were species-specific. The stock and/or conservation status overall contributed the most to higher sensitivity. Between 1989 and 2019, species with low and moderate sensitivity dominated regional landings, regardless of the jurisdiction analyzed. A considerable fraction of these landings consisted of species scoring high or very high on an indicator for potential to change their current distribution. These results suggest that although the bulk of past landings were from relatively climate-resilient species, future catches and even entire benthic fisheries may be jeopardized because (1) some exploited species showed high or very high sensitivities and (2) the increase in the relative representation of landings in species whose distribution may change. This paper provides novel results and insights relevant for fisheries management from a region where the effects of climate change have been overlooked, and which lacks a coordinated governance system for climate-resilient fisheries.

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MCCIP 2022 ocean acidification (audio & video)

Published 24 March 2023 Presentations , Resources Closed
MCCIP update: A decline in pH (increasing acidity) is evident through the global ocean, and rates could increase in the second half of the century. For UK shelf seas, the rate of pH decline is higher in some coastal areas than others. Lead author: Dr Helen Findlay, Plymouth Marine Laboratory.
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Survey to assess ocean acidification research capacity and interest in the Caribbean

Published 24 March 2023 Web sites and blogs Closed

Link to Survey: Survey to Assess Ocean Acidification Research Capacity and Interest in the Caribbean

Description: This survey is being conducted by a Community of Practice (CoP) for Ocean Acidification in the Caribbean in collaboration with The Ocean Foundation. This group seeks to create a strategic framework and funding plan to enable increased capacity to monitor and respond to ocean change in the Caribbean, with a focus on ocean acidification. The results of this survey will assist the Caribbean CoP in seeking appropriate partners and funding to meet the needs of the region.

There are four sections of this survey. Please fill in all questions that are relevant to your work to the best of your ability.

The survey will be open until April 21, 2023. The CoP aims to report on survey results via email and at local conferences (i.e. AMLC Meeting in St. Kitts May 22-26, 2023). The overall goal is to better inform policymakers and funding agencies in the region about OA. 

The survey is only available in English. Chrome provides web page translation via google translate. You may answer the long form questions in your preferred language.

We invite you to share this survey with any additional colleagues whose work is relevant to the activities of the CoP.
If you have any questions about the survey, please contact Alexis Valauri-Orton (avalauriorton@oceanfdn.org)

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The ocean carbon and acidification data system

Published 23 March 2023 Science Closed
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The Ocean Carbon and Acidification Data System (OCADS) is a data management system at the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information (NCEI). It manages a wide range of ocean carbon and acidification data, including chemical, physical, and biological observations collected from research vessels, ships of opportunity, and uncrewed platforms, as well as laboratory experiment results, and model outputs. Additionally, OCADS serves as a repository for related Global Ocean Observing System (GOOS) biogeochemistry Essential Ocean Variables (EOVs), e.g., oxygen, nutrients, transient tracers, and stable isotopes. OCADS endeavors to be one of the world’s leading providers of ocean carbon and acidification data, information, products, and services. To provide the best data management services to the ocean carbon and acidification research community, OCADS prioritizes adopting a customer-centric approach and gathering knowledge and expertise from the research community to improve its data management practices. OCADS aims to make all ocean carbon and acidification data accessible via a single portal, and welcomes submissions from around the world: https://www.ncei.noaa.gov/products/ocean-carbon-acidification-data-system/.

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Ocean acidification impedes foraging behavior in the mud snail Ilyanassa obsoleta

Published 23 March 2023 Science Closed
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Ocean acidification may diminish the response of many marine organisms to chemical cues that can be used to sense nearby food and predators, potentially altering community dynamics. We used a Y-maze choice experiment to investigate the impact of ocean acidification on the ability of mud snails (Ilyanassa obsoleta) to sense food cues in seawater. Mud snails have a well-adapted chemosensory system and play an important role in estuarine ecosystem functioning. Our results showed substantially diminished foraging success for the mud snail under acidified conditions, as snails typically moved towards the food cue in controls (pH 8.1) and away from it in acidified treatments (pH 7.6). These results, coupled with previous work, clearly demonstrate the magnitude at which ocean acidification may impair foraging efficiency, potentially resulting in severe alterations in future ecosystem dynamics.

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Metabolomics approach to reveal the effects of ocean acidification on the toxicity of harmful microalgae: a review of the literature

Published 23 March 2023 Science Closed
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Graphical abstract

Climate change has been associated with intensified harmful algal blooms (HABs). Some harmful microalgae produce toxins that accumulate in food webs, adversely affecting the environment, public health and economy. Ocean acidification (OA) is a major consequence of high anthropogenic CO2 emissions. The carbon chemistry and pH of aquatic ecosystems have been significantly altered as a result. The impacts of climate change on the metabolisms of microalgae, especially toxin biosynthesis, remain largely unknown. This hinders the optimization of HAB mitigation for changed climate conditions. To bridge this knowledge gap, previous studies on the effects of ocean acidification on toxin biosynthesis in microalgae were reviewed. There was no solid conclusion for the toxicity change of saxitoxin-producing dinoflagellates from the genus Alexandrium after high CO2 treatment. Increased domoic acid content was observed in the diatom Pseudo-nitzschia. The brevetoxin content of Karenia brevis remained largely unchanged. The underlying regulatory mechanisms that account for the different toxicity levels observed have not been elucidated. Metabolic flux analysis is useful for investigating the carbon allocations of toxic microalgae under OA and revealing related metabolic pathways for toxin biosynthesis. Gaining knowledge of the responses of microalgae in high CO2 conditions will allow the better risk assessment of HABs in the future.

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New study suggests acidification from climate change could harm sea scallop populations

Published 23 March 2023 Media coverage , Web sites and blogs Closed

Jamie Sewell of Warren prepares his boat for a scallop diving off the coast of Cushing in January 2015. Gabe Souza/Staff Photographer, file.

A new study co-authored by federal scientists and Massachusetts Maritime Academy staff and students suggests that increased ocean acidification could pose a threat to the sea scalloping industry in the Gulf of Maine and elsewhere along the Atlantic seaboard.

It marks the first time that the impact of ocean acidification on sea scallops has been studied to this extent.

In an eight-week research project, scientists with the National Oceanic and Atmospheric Administration collaborated with the academy to conduct the study at the school’s aquaculture lab on Buzzards Bay in Massachusetts. They concluded that ocean acidification could significantly depress Atlantic sea scallop productivity in the years ahead.

Their study, which was published March 1, also found that pH levels – the measure of acidity – in the Gulf of Maine are dropping faster than at other locations on the East Coast, meaning acidity is increasing. Ocean acidification rises as the ocean absorbs more carbon dioxide from the atmosphere.

…

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The effects of light intensity and flow speed on biogeochemical variability within a fringing coral reef in Onna-Son, Okinawa, Japan

Published 22 March 2023 Science Closed
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Abstract

Global warming and ocean acidification are driving declines in seawater dissolved oxygen (DO) concentrations and pH. Predicting how these changes will affect shallow, near-shore environments such as coral reefs is challenging due to their high natural biogeochemical variability present over both spatial (m to km) and temporal (diel to seasonal) scales. To make predictions, we must understand the drivers of this variability. The impact of metabolic processes on coral reef biogeochemical variability has been the subject of significant research effort, however, physical factors, including flow speed and light intensity, have received less attention. Here, we measured seawater flow, photosynthetically active radiation (PAR), pH, and DO at three reef habitats (reef flat, lagoon, and outflow channel) in a fringing coral reef system in Okinawa, Japan for 3 weeks in October 2019. During the study, pH ranged from 7.86 to 8.37 units while DO varied from 127 to 369 μmol/kg. Circulation was primarily wave-driven with mean flow speeds ranging from 14 to 26 cm/s. Flow direction became increasingly consistent at higher flow speeds and traced benthic striations visible in satellite imagery. Multiple linear regression models of daytime changes in pH and DO versus daily mean flow speed and PAR described 25%–74% of the observed variability across all sites while at night, flow speed alone accounted for 7%–75% of the observed variability. These results demonstrate PAR, water flow speed, and the path water takes play important roles in controlling biogeochemical variability within coral reefs and must be considered when assessing their vulnerability to both local and global environmental change.

Key Points

  • Flow speed and light intensity explained 25%–74% of daily and 7%–75% of nightly pH and oxygen variability across different reef habitats
  • Circulation of the Onna-son coral reef system was driven by waves, but modulated by tides, and was highly consistent
  • Constraining coral reef circulation and light intensity will allow us to better predict future biogeochemical variability on coral reefs
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