Ocean Acidification

The eight most common species of coral around the islands can adapt to ocean warming and acidification but only if efforts to cut carbon emissions are made, according to a new study by researchers at the University of Hawaiʻi at Mānoa Hawaiʻi Institute of Marine Biology (HIMB).  

Throughout the Indo-Pacific, a region that comprises more than two-thirds of the coral reefs on Earth, corals were found to be capable of surviving a “low climate change scenario,” where laboratory conditions reflect a global reduction in carbon dioxide emissions. Critically, none of the species in the study could withstand a scenario where carbon emissions were not reduced. The study published in Proceedings of the Royal Society B suggests that curtailing carbon dioxide emissions is essential for the survival of coral reefs.  

“This study shows that widespread and diverse coral species all exhibit the potential to adapt to the changing climate, but climate change mitigation is essential for them to have a chance at adaptation,” said Christopher Jury, who is an HIMB post-doctoral researcher and lead author of the study. 

Massive reef structures are formed over time. Growth is gradual; some coral colonies grow less than an inch each year, and researchers use coral growth rate as an indicator of reef ecosystem health. For nearly one year, the research team simulated realistic field conditions. They controlled levels of temperature and acidity, and measured the calcification responses of the eight species of coral. 

“When we analyzed how the corals performed under warmer, more acidic conditions, we found that about one quarter to one half of their tolerance is inherited through their genes,” said Robert Toonen, research professor at HIMB and principal investigator of the project. “That means the ability to survive under future ocean conditions can be passed along to future generations, allowing corals to adapt to ocean warming and acidification.”

“This was a very surprising result, given the usual projected collapse of coral reefs in Hawai‘i and globally under these climate change stressors,” said Jury. “Most projections are that corals will be almost entirely wiped out, and coral reefs will collapse within the next few decades because corals cannot adapt fast enough to make a meaningful difference. This study shows that is not true, and we still have an opportunity to preserve coral reefs.”

The ability for corals to adapt to combined warming and acidification will play a key role in their responses to global change over coming decades. Most studies examining their ability to adapt have focused on heat tolerance. Far less is known about corals’ capacity to adapt to more acidic conditions, and very few studies have examined their capacity to adapt to the combination of warming and acidification. Evidence indicates they may be better at adapting to the changing climate.

“By understanding how these species respond to climate change, we have a better understanding of how Hawaiian reefs will change over time and how to better allocate resources as well as plan for the future,” said Jury.

Funding was provided by the National Science Foundation, UH Sea Grant College Program, and the National Oceanic and Atmospheric Administration’s Ocean Acidification Program.

• A first of its kind Planetary Health Check by an international team of scientists indicates that six of nine planetary boundaries are not only transgressed, but are moving further into zones of risk. In addition, recent research shows that a seventh boundary, ocean acidification, is on the verge of transgression.
• Intensifying ocean acidification spells problems for marine life, fisheries and economies. Based on current human CO₂ emission trajectories, this boundary may be breached in a few years, say experts. Others argue this threshold may already have been crossed, with regional acidification above safe limits.
• Together, the nine planetary boundaries identify limits within which Earth systems can operate safely to maintain the planet’s habitability. Transgressing boundaries heightens risks of breaching tipping points that would bring about irreversible shifts to the planet, threatening humanity and life as we know it.
• This inaugural Planetary Health Check is the first of yearly scheduled reports on the wellbeing of Earth systems. Annual reports are now needed due to humanity’s rapid crossing of planetary boundaries, and due to the urgency of providing up to date scientific data to policymakers.

The first ever pulse check of the planet’s health shows that the Earth is far beyond it’s safe operating space for humanity. Six of nine key planetary boundaries are already transgressed, and continue moving deeper into risk zones that could threaten our planet’s habitability. A seventh boundary, ocean acidification, is on the verge of transgression and may exceed safe limits in a matter of years.

That’s according to the first-ever Planetary Health Check, a nearly 100 page report produced by the new Planetary Boundaries Science (PBScience) initiative led by Earth System scientist Johan Rockström and the Potsdam Institute for Climate Impact Research (PIK), and supported by the Planetary Guardians and other partners.

Boundaries for climate change, biosphere integrity, land system change, freshwater change, biogeochemical flows, and the introduction of novel entities (such as synthetic chemical pollutants) are all surpassed, as a study published last year found.

Worryingly, in this latest report, all those already transgressed are moving deeper into the red zone, says Levke Caesar, a report author and co-leader on planetary boundaries at the Potsdam Institute for Climate Impact. “Our updated diagnosis shows that vital organs of the Earth system are weakening, leading to a loss of resilience, and rising risks of crossing [irreversible] tipping points.

“We see it’s not changing [for the better]. It is actually getting worse,” she says.

The breach of planetary boundaries heightens the risk of permanently damaging Earth’s life support functions, with the report warning that the world is entering a “dangerous new era.” Symptoms of boundary transgression already being seen include the rapid extinction of species, extreme heat, drought and storms, record wildfires, reduced crop and fisheries productivity, and freshwater scarcity.

“We are really risking losing the planet as we know it, and this risk is increasing the further we go into the red zones,” Caesar adds.

Worse still, the health check found that the ocean acidification boundary is nearing transgression, and may pass its global “safe operating space” threshold in the next few years, says Caesar. Acidification — driven by climate change-fueling CO₂ emissions — could severely impact marine ecosystems and the global economy.

Graphic showing that six of the nine planetary boundaries have already transgressed the “safe operating space for humanity,” with ocean acidification on the verge of entering the red zone. Stratospheric ozone depletion is considered stable, while only atmospheric aerosol loading is trending in a positive direction. Image from Planetary Health Check 2024, designed by Globaïa.

Ocean health on the brink

For now, the ocean acidification boundary remains within the green safe operating space, according to scientists, but it is on the precipice. Studies show rising acidification could devastate fragile coral reefs and phytoplankton populations, considered the foundation of marine food webs. As acidification accelerates, global fisheries could degrade and even collapse, deepening human suffering and worsening hunger in vulnerable communities, and inflicting billions of dollars in global costs to economies.

Ocean acidification is driven by the same cause as climate change: rising atmospheric CO₂ concentrations due to rampant fossil fuel emissions. The outlook for staying within the safe limit for this boundary appears bleak. “Looking at the current evolution, I’d say it’s really, really difficult to prevent that [boundary] crossing,” Caesar says.

The report uses surface aragonite saturation as an indicator for ocean acidification because it correlates to carbonate ion concentration. As atmospheric carbon dioxide is absorbed by the ocean, more-and-more carbonic acid is created, which releases hydrogen ions to lower pH and aragonite saturation. Declining pH in seawater means more ocean acidity and spells trouble for marine life that relies on calcium carbonate for shell formation.

The current safe operating limit is set at 2.75 aragonite saturation and is based on pre-industrial levels of 3.44. Levels below 3 can lead to some marine organisms becoming stressed, and if levels drop below 1 shells can begin to dissolve. Today, global aragonite saturation stands at 2.80. Passing that safe limit does not mean an immediate drop off a cliff, explains Caesar, but problems for marine life and the ocean’s food web will “definitely start to look more and more severe.”

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Report: Caesar, L., Sakschewski, B., Andersen, L S., Beringer, T., Braun, J., Dennis, D., Gerten, D., Heilemann,. A., Kaiser, J., Kitzmann, N.H., Loriani, S., Lucht., W Ludescher, J., Martin, M., Mathesius, S., Paolucci, A., te Wierik, S., & Rockström, J. (2024), Planetary Health Check Report 2024. Potsdam Institute for Climate Impact Research, Potsdam, Germany.

Ph.D. candidate Abigail Sisti works in the Seawater Research Lab at VIMS. Credit: Brittany Jellison

According to a study by researchers at William & Mary’s Batten School of Coastal & Marine Sciences, the American lobster may be more resilient to the effects of climate change than expected. For the first time, experiments performed at the Virginia Institute of Marine Science (VIMS) have documented how female American lobsters groom their offspring, providing evidence that these behaviors are not significantly impacted by temperature and acidity levels forecasted for Maine’s coastal waters by the end of the century.

The findings are published in the journal Marine Ecology Progress Series.

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“Brood grooming by female lobsters has been anecdotally observed, but it had not been quantitatively recorded before,” said Abigail Sisti, who is completing her Ph.D. in Marine Science at the Batten School and is lead author on the study. “In other crustaceans, these behaviors can have a significant impact on the survival of their offspring. Because the environment supporting the lobster fishery is rapidly changing, we wanted to understand how it might impact the way they care for their offspring.”

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The study was part of a larger effort to determine how multiple stressors affect the reproductive success of the species. In this study, the researchers were testing whether increases in water temperatures and acidity had an impact on grooming behaviors and embryo survival.

“The long-term nature of this experiment required somewhat of a moonshot approach,” said Rivest, whose seawater aquarium laboratory at VIMS has been specifically designed to control multiple environmental variables over long periods of time. “The conditions of our control group were set to match current conditions in the Gulf of Maine, while our experimental groups corresponded to temperature and pH predictions for the end of the century.”

In addition to their research outcomes, Sisti and others produced an educational curriculum to involve students and teachers in the research. The research as well as the lesson plans are documented through a story map produced by the National Oceanic and Atmospheric Administration’s Sea Grant and Ocean Acidification Program.

Documenting grooming behavior

The researchers partnered with officials from Maine’s Department of Marine Resources to secure lobsters from commercial operations for use in the study. They obtained female lobsters at a marketable size with intact legs, which are frequently lost in the wild or when they are caught. In total, they observed the behavior of 24 lobsters for five months, or until the embryos matured. Sisti and other students had the daunting task of reviewing dozens of hours of recordings from underwater cameras and documenting the frequency and type of grooming behaviors as well as the overall survival of the embryos.

Lobsters in experimental groups experienced temperature increases of 4 degrees Celsius and acidification levels of -0.5 pH from present conditions. Oxygen levels remained constant for all animals to isolate the effects of temperature and acidity.

Sand sample from Elafonisos, Greece, with abundant A. lobifera shells, as well as shells and shell fragments from snails and other organisms. Credit: Olga Koukousioura

Pamela Hallock, a biogeological oceanographer and distinguished university professor at the University of South Florida College of Marine Science, typically finds little comfort in climate change.

Hallock has spent her career studying the ocean. She leads USF’s Reef Indicators Lab and is no stranger to the impacts of human activities on marine environments.

Still, she couldn’t help but notice a bright spot in the results of her recent paper on a species of single-celled organisms called foraminifera (forams), published in the Journal of Foraminiferal Research.

“These forams have been increasing in numbers in suitable environments,” Hallock said. “Now they’re so prolific that they’re becoming an economic resource in regions with warm waters and high alkalinity because they’re building beaches.”

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Amphistegina lobifera. Credit: Olga Koukousioura

“The rate at which these forams are building beaches in the region is comparable to the rate of sea level rise,” Hallock said.

There’s reason to believe A. lobifera may continue to flourish in a warming world replete with atmospheric CO₂. The genus Amphistegina emerged on Earth during a period of higher atmospheric CO₂ concentrations, Hallock noted in her paper, and warm waters with elevated alkalinity increase their rates of metabolism and shell formation.

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The recent study offers a unique perspective about the impacts of humans on marine environments, and vice versa.

As Hallock and her co-authors state in the study, “Might this return of prolific shallow-water carbonate production ultimately prove at least locally beneficial as climate change progresses?”

Rainfall on the ocean’s surface is responsible for around 6% of the ocean’s uptake of carbon dioxide. Credit: Miguel Alcantara.

The ocean plays an important role in the global carbon cycle by absorbing about one-quarter of the carbon emitted by human activities every year. A study published recently in Nature Geoscience and co-authored by a University of Hawai‘i at Mānoa oceanographer revealed about 6% of the total uptake of carbon dioxide (CO₂) by the ocean is due to rainfall.  

“The impact of rain on air-sea CO₂ fluxes hasn’t been systematically examined, but understanding it gives us a more complete picture,” said David Ho, study co-author and oceanography professor in the UH Mānoa School of Ocean and Earth Science and Technology. “This is especially important since rainfall patterns over the ocean are expected to shift with climate change, and that could impact the ocean carbon sink.”

Exchanges between the ocean and the atmosphere are governed by various chemical, physical, and biological properties and processes. Rainfall alters these properties of the ocean surface, and thus promotes the exchange of CO₂ at the air-sea interface. 

Rain impacts this carbon exchange in three different ways. First, as it falls on the ocean surface, it generates turbulence that facilitates the renewal of water in contact with the atmosphere. Secondly, it dilutes the seawater at the surface, altering the chemical equilibrium within the oceanic carbon cycle and enabling seawater to absorb greater quantities of CO₂. Finally, raindrops directly inject CO₂ absorbed during their fall into the ocean through wet deposition.

Connecticut and Houstatonic river discharge and ratios of dissolved organic carbon to total alkalinity for the tributaries and west Long Island Sound across the study interval of 2020–2022. Credit: Frontiers in Marine Science (2024). DOI: 10.3389/fmars.2024.1398087

New York’s Long Island Sound (LIS) is an important inlet and estuary in the North Atlantic Ocean, which is highly urbanized due to its proximity to the city. This daily activity of passenger transport, fishing and cargo ships has had significant consequences on the marine landscape here, resulting in environmental degradation that impacts the flora and fauna that call LIS home.

Deep sea coral (NOAA file image). The zone where carbonate-containing life forms like these dissolve is set to expand by about 14 million square miles.

In the deepest parts of the ocean, below 4,000 meters, the combination of high pressure and low temperature creates conditions that dissolve calcium carbonate, the material marine animals use to make their shells.

This zone is known as the carbonate compensation depth – and it is expanding.

In the deepest parts of the ocean, below 4,000 metres, the combination of high pressure and low temperature creates conditions that dissolve calcium carbonate, the material marine animals use to make their shells.

This zone is known as the carbonate compensation depth – and it is expanding.

This contrasts with the widely discussed ocean acidification of surface waters due to the ocean absorbing carbon dioxide from the burning of fossil fuels.

But the two are linked: because of rising concentrations of carbon dioxide in the ocean, its pH is decreasing (becoming more acidic), and the deep-sea area in which calcium carbonate dissolves is growing, from the seafloor up.

The transition zone within which calcium carbonate increasingly becomes chemically unstable and begins to dissolve is called the lysocline. Because the ocean seabed is relatively flat, even a rise of the lysocline by a few metres can rapidly lead to large under-saturated (acidic) areas.

Our research showed this zone has already risen by nearly 100 metres since pre-industrial times and will likely rise further by several hundreds of metres this century.

Millions of square kilometres of ocean floor will potentially undergo a rapid transition whereby calcareous sediment will become chemically unstable and dissolve.

Expanding boundaries

The upper limit of the lysocline transition zone is known as the calcite saturation depth, above which seabed sediments are rich in calcium carbonate and ocean water is supersaturated with it. The calcite compensation depth is its lower limit, below which seabed sediments contain little or no carbonate minerals.

The area below the calcite compensation depth varies greatly between different sectors of the oceans. It already occupies about 41% of the global ocean. Since the industrial revolution, this zone has risen for all parts of the ocean, varying from almost no rise in the western Indian Ocean to more than 300 metres in the northwest Atlantic.

If the calcite compensation depth rises by a further 300 metres, the area of seafloor below it will increase by 10% to occupy 51% of the global ocean.

Distinct habitats

For the first time, a recent study showed the calcite compensation depth is a biological boundary with distinct habitats above and below it. In the northeast Pacific, the most abundant seabed organisms above the calcite compensation depth are soft corals, brittle stars, mussels, sea snails, chitons and bryozoans, all of which have calcified shells or skeletons.

However, below the calcite compensation depth, sea anemones, sea cucumbers and octopus are more abundant. This under-saturated (more acidic) habitat already limits life in 141 million square kilometres of the ocean and could expand by another 35 million square kilometres if the calcite compensation depth were to rise by 300 metres.

In addition to the expansion of the calcite compensation depth, parts of the ocean in low latitudes are losing species because the water is getting too warm and oxygen levels are declining, both also due to climate change.

Thus, the most liveable habitat space for marine species is shrinking from the bottom (rising calcite compensation depth) and the top (warming).

Island nations most affected

The exclusive economic zones of some countries will be more affected than others. Generally, oceanic and island nations lose more, while countries with large continental shelves lose proportionately less.

Bermuda’s EEZ is predicted to be the most affected by a 300-metre rise of the calcite compensation depth above the present level, with 68% of that country’s seabed becoming submerged below the lysocline. In contrast, only 6% of the US EEZ and 0.39% of the Russian EEZ are predicted to be impacted.

From a global perspective, it is remarkable that already 41% of the deep sea is effectively acidic, that half may be by the end of the century, and that the first study showing its effects of marine life was only published in the past year.

“Oceans aren’t just a nice backdrop for your selfies in summer…”

The world’s oceans are in hot water, and it’s not just because of Earth’s overheating.

What’s happening?

The world’s oceans are confronting a “triple threat” of extreme heating, oxygen loss, and acidification. As reported by the Guardian, this alarming trend, driven by human activities such as pollution and deforestation, has escalated dramatically in recent decades. 

Research published in AGU Advances reveals that about a fifth of the world’s ocean surface is particularly vulnerable to these compound threats. In the top 300 meters of the ocean, these extreme conditions now last three times longer and are six times more intense than in the 1960s. 

Joel Wong, lead author of the study and researcher at ETH Zurich, emphasized that the climate crisis is pushing our oceans into a dangerous new state.

The impacts of this have already been seen and felt. Intense extreme events like these are likely to happen again in the future and will disrupt marine ecosystems and fisheries around the world,” Wong said, via the Guardian.

A new study of coral reefs in Papua New Guinea shows ocean acidification simplifies coral structure, making crucial habitat less appealing to certain fish species.

While much media attention has focused on heat stress-induced coral bleaching, this finding, by a University of Adelaide research team led by Professor Ivan Nagelkerken, adds nuance to concerns about how global warming affects coral reefs.

Ocean acidification is caused by an increase in the level of carbon dioxide in oceanwater, leading to a reduction in pH. This makes calcium carbonate less available in the ocean, which corals use to build and repair their skeleton.

Professor Nagelkerken and his team show that, while ocean acidification in some instances does not reduce overall coral cover on a reef, the structures are less branched and therefore less appealing as habitat to some fish species.

Researchers observed two reefs in Upa-Upasina, Papua New Guinea: one located next to a volcanic seep releasing a steady stream of carbon dioxide, causing natural acidification, and another located 500 metres away unaffected by the volcanic gases.

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“Ocean acidification has the potential to reshuffle ecological communities globally, lead to the loss of key habitats and biodiversity, reduce fisheries’ productivity, and have negative physiological impacts on many marine animals and plants,” says Professor Nagelkerken, from the University of Adelaide’s School of Biological Sciences.

“It might also lead to a reduction in populations of various fish species, which could create novel species community structures that might have lower biodiversity and not be as resilient as present-day communities. It could also clearly distinguish winner species from loser species. And if this ocean acidification affects fisheries species, some species that recreational and commercial fishers target might become less abundant.”

The acidification conditions observed in the research, which was published in the Journal of Animal Ecology, at the reef beside the volcanic seep are expected to occur in the ocean more broadly as the increasing level of human-caused carbon emissions in Earth’s atmosphere are absorbed by the ocean.

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Credit: NEOM/ Unsplash

A new study of coral reefs in Papua New Guinea shows ocean acidification simplifies coral structure, making crucial habitat less appealing to certain fish species.

While much media attention has focused on heat stress-induced coral bleaching, this finding, by a University of Adelaide research team led by Professor Ivan Nagelkerken, adds nuance to concerns about how global warming affects coral reefs.

Ocean acidification is caused by an increase in the level of carbon dioxide in oceanwater, leading to a reduction in pH. This makes calcium carbonate less available in the ocean, which corals use to build and repair their skeleton.

Lemon Damselfish and Dascyllus at a shallow coral reef. Credit: Placebo365/iStock.

A new study of coral reefs in Papua New Guinea shows ocean acidification simplifies coral structure, making crucial habitat less appealing to certain fish species.

While much media attention has focused on heat stress-induced coral bleaching, this finding, by a University of Adelaide research team led by Professor Ivan Nagelkerken, adds nuance to concerns about how global warming affects coral reefs.

Ocean acidification is caused by an increase in the level of carbon dioxide in oceanwater, leading to a reduction in pH. This makes calcium carbonate less available in the ocean, which corals use to build and repair their skeleton.

The French Polynesian island Moorea is the most beautiful isle in the world, some say. Its lagoons are surrounded by reefs dominated by Porites corals.  

These corals and other calcifying marine species are the world’s primary reef-builders. Therein lies the trouble. The seas in which they dwell are turning acidic, a result of rising atmospheric carbon dioxide (CO2). Marine life that depends on calcium carbonate struggles to form shells or, in the case of coral reefs, skeletons.   

Porites reefs, say scientists Peter Edmunds and Robert Carpenter of California State University at Northridge, are among the most sensitive of all corals. Edmunds, Carpenter and Steve Doo of the University of Hawaii published results in the journal Limnology and Oceanography revealing the consequences of ocean acidification. The reefs may not be able to grow and reproduce.

In the actual context of global changes, ocean warming and acidification are both closely related to increased atmospheric carbon dioxide concentration and are expected to deeply impact biological communities through generalized effects on the entire oceanic system. Indeed, environmental changes may challenge the growth and stability of various marine productions due to the emerging consequences associated with ocean warming and acidification. Among commercial marine species, sea urchins undergo a variety of physiological, transcriptomic and immunological changes as a result of the conditions imposed by ocean warming and acidification, raising questions about the future management of several populations.

In addition to their importance in terms of ecological services, sea urchins are widely exploited for commercial purposes, supporting a growing market of considerable value. Although recent studies emphasize the growing importance of echinoid farming within integrated multitrophic aquaculture (IMTA) systems, sea urchin fisheries account for more than 99.9 percent of total sold per year, with aquaculture providing the remainder.

A school of yellowmouth barracudas in Scandola Marine Reserve, Corsica, France on June 17, 2017

A new study has found that the planet’s oceans are experiencing a “triple threat” of oxygen loss, extreme heat and acidification.

The researchers discovered that, as global heating has worsened, increasing stress has been placed on marine species, with as much as 20 percent of the world’s oceans affected by these threats.

“The global ocean is becoming warmer, more acidic, and losing oxygen due to climate change. On top of this trend, sudden increases in temperature, or drops in pH or oxygen adversely affect marine organisms when they cannot quickly adapt to these extreme conditions,” the study said.