Keywords: Climate change, Water quality, Species and food webs, Algae, Fishes, Invertebrates, Marine habitat

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Ocean acidification, which has begun to endanger sea life throughout the world, is impairing Pacific Northwest waters — including the Salish Sea — sooner than most regions around the globe, according to ongoing studies focused on ocean circulation.

Even more alarming is new research now causing oceanographers to predict that potentially devastating changes in ocean chemistry will soon pick up the pace, bringing acidification faster and faster with ever more dire effects over the coming years.

“If we continue down the road we are on, we will see very dramatic changes in the next 10 to 20 years,” said Richard Feely, senior scientist at NOAA’s Pacific Marine Environmental Laboratory in Seattle.

Ocean acidification, caused by the absorption of more and more carbon dioxide from the atmosphere, can affect the growth and behavior of all kinds of sea creatures. New evidence suggests that salmon could lose their sense of smell and get lost on their way home, that herring and other critical prey species could fail to grow, and that unsung plankton communities could die off, altering the food web.

Most notable in the struggle for survival amid ocean acidification are species that form shells of calcium carbonate — including succulent oysters that support a vast industry, colorful corals that create diverse habitats, and a wide variety of tiny animals that sustain the entire web of life.

Oyster harvested at Henderson Inlet, WA. Photo: NRCS

Oyster harvested at Henderson Inlet, WA. Photo: NRCS

These new predictions are the result of a growing understanding of the chemical changes taking place in different parts of the ocean, said Feely, who presented the latest findings during the recent Ocean Acidification Science Symposium in Seattle. Of particular concern, he noted, is what could become a dangerous weakening of the ocean’s buffers — an elegant set of chemical reactions that have so far inhibited an even faster rate of ocean acidification.

Researchers at the symposium also presented new findings about the effects of ocean acidification on salmon, herring, Dungeness crabs, plankton and eelgrass, while others talked about future conditions and what can be done to turn things around.

Ocean chemistry

Over the past decade, scientists throughout the world have been joining forces to better understand ocean acidification and the resulting ecological damage. The Global Ocean Acidification Observing Network, known as GOA-ON, has been compiling and sharing data from a vast array of sources —from stationary monitoring buoys to ocean-going research vessels to merchant ships that deploy sensory equipment while delivering cargo around the world.

Researchers have long understood that the ocean is far from uniform when it comes to absorbing and transforming excess carbon dioxide, said Feely, who has been studying ocean acidification for 37 years. New information is helping to explain why Northwest waters are so vulnerable to acidification and why the perils are growing greater as time goes by.

As carbon dioxide increases in the atmosphere from the burning of fossil fuels, about 30 percent of it gets absorbed into the ocean, where it transforms into other carbon compounds. Such compounds have been building up in narrow bands across the ocean immediately north and south of the tropics. The buildup results largely from a combination of temperature, ocean currents and the chemical properties of ocean water.

In the North Pacific, subsurface currents along the West Coast carry acidified water northward, where upwelling brings corrosive low-oxygen water up from the depths. That’s why shell-bearing creatures in Washington, Oregon and Northern California have already become more vulnerable to ocean acidification than almost anywhere on Earth.

New studies on pteropods — free-swimming sea snails — have revealed that the shells of these tiny animals collected along the coast are fully one-third thinner than those of pteropods collected in the open ocean. Such studies raise concerns not only for the survival of pteropods but the future of the entire food web.

Pterapod shell shown dissolving over time. Photo: NOAA Environmental Visualization Laboratory

In laboratory experiments, a pterapod shell dissolved over the course of 45 days in seawater adjusted to an ocean chemistry projected for the year 2100. Photo: NOAA Environmental Visualization Laboratory

New evidence also suggests that acidification has already begun to upset the chemical balance of the ocean, including its ratio of buffering chemicals, which so far have helped to quell the rate of acidification. But buffering has its limits. Once a threshold is reached, the rate of acidification is expected to accelerate, like a brakeless freight train on a downhill track.

The chemistry of the ocean is complex, but buffering can be viewed as a balance between two closely related compounds — with carbonate and bicarbonate being the key partners. They can readily change form from one to the other as acidity increases or decreases. This partnership helps to maintain a fairly stable pH — the common measure of acidity. 

Buffering comes into play as the ocean absorbs carbon dioxide through direct contact with the atmosphere. As CO2 gas enters the water, it readily converts to carbonic acid and begins to influence the buffer, turning carbonate into bicarbonate. As carbonate is consumed, the rate of acidification increases.

At the same time, the increase in carbon dioxide also influences the concentration of calcium carbonate  — the material of shells. Higher acidity tends to dissolve calcium carbonate molecules into separate calcium and carbonate ions. Thereafter, the reduced concentration of calcium carbonate makes this critical mineral less accessible to the shell-forming animals. At low concentrations of carbonate, favorable chemical reactions can actually run in reverse, dissolving the shells of living creatures.

If concerns about coastal waters are running high, trends for Puget Sound and the entire Salish Sea are raising the loudest alarm bells, Feely said. That’s because freshwater flowing in from rivers and streams lowers the buffering capacity even further through dilution.

In addition, excess nutrients from natural and human sources, such as sewage-treatment plants, are encouraging the growth of algae, which eventually die and decay, leaving an oxygen deficit and even more carbon dioxide to upset the natural balance.

“We compared the changes in the open ocean right outside the Strait of Juan de Fuca to the changes in Puget Sound on a year-to-year basis,” Feely said. “Puget Sound, the Salish Sea, has much lower pH (higher acidity) and more rapid change because of the lower buffer capacity.”

It turns out that harmfully low levels of calcium carbonate are seen in Puget Sound even more frequently than harmful oxygen levels, according Simone Alin, a colleague of Feely at NOAA’s PMEL.

Continuing on the present course, the outcome will be increasing injury, impairment and death for marine life in inland waterways — and not just for the Salish Sea but for San Francisco Bay in California and for Prince William Sound in Alaska, Feely told attendees at the ocean acidification symposium.

“Many West Coast estuaries with freshwater inputs will see these impacts,” he said.

Once the buffering capacity reaches a critical threshold, the increase in acidification will come rapidly, Feely said, and the cascading effects on marine life will be felt throughout the ecosystem.

“We’re not there yet, but we’re at a turning point,” he said. “We have to make a decision about what we are going to do. The result (for marine life) will be a function of our decisions.”

Effects on fish

If ocean acidification continues to intensify, researchers predict uncertain but profound changes in the food web, as each species adjusts to its new conditions — or else dies. For shell-building creatures, the lack of calcium carbonate in the water may be observed as weaker shells, assuming the animal can survive. For other animals, behavioral changes may be the most dangerous problem, although behavior can be difficult to study.

Experiments on coho salmon, for example, have shown that when they are in marine waters with low pH (higher acidity), their ability to avoid predators declines and the risk of being eaten rises dramatically.

The cause may be related to changes in blood chemistry and effects on the fish’s ability to sense chemicals in the water, according to researcher Chase Williams and his colleagues at the University of Washington’s Department of Environmental and Occupational Health Sciences and NOAA’s Northwest Fisheries Science Center.

Specifically, the lower pH causes the fish to accumulate more bicarbonate to maintain a stable blood pH, which leads to an excretion of chloride ions, Williams said at the ocean acidification symposium.

“This is important, because the chloride concentration across the cellular membrane in the brain is critical in the signaling pathway,” he said. “When you start reversing certain signals, you start altering the code.”

Using special instruments, Williams’ team was able to find faulty signals in the connections with the olfactory centers responsible for the sense of smell. Fish could smell the odors, but disruptions in the neural pathway altered how they reacted to smells picked up from the water. If a fish can’t tell the difference between predator and prey, it probably won’t last long in the real world.

Salmon also use their sense of smell for mating and finding their way back to their natal waters, Williams said, so learning how a fish responds to different pH levels could determine their chances of survival.

Changes in pH are not the only issue, he noted, because salmon face many other challenges, such as increasing temperatures and low oxygen levels, which also are influenced by climate change. Further studies are focusing on other species of salmon, and Williams is looking into how ocean acidification might affect how the fish use the Earth’s magnetic field to find their way in the open ocean.

Another type of fish creating a lot of interest is Pacific herring, which serves as primary prey for salmon as well as a variety of other marine creatures. Among the first to study the effects of changing ocean conditions on these forage fish is Associate Professor Brooke Love along with graduate student Cristina Villalobos, both at Western Washington University.

Herring were fertilized and hatched in water under normal conditions as well as in water with low pH, similar to what might be seen in Puget Sound in the year 2100. More fish died in the water with the lower pH, Love said. Higher water temperatures, such as future conditions in Puget Sound, produced a similar but even more powerful effect.

Together, higher temperature and lower pH were shown to increase the death rate from around 20 percent to more than 50 percent, said.

“The conditions we tested are not so far off from what we might expect in the future, so the findings are worrisome,” she said, “but this is just one study, so more testing is needed.”

Future studies on herring are being planned to:

  • Examine the effects of rearing the fish at various other temperatures;
  • consider whether different populations of herring respond in different ways; and
  • determine what physiological changes are triggered by higher temperature and lower pH.

Dungeness crab

Knowing that Dungeness crabs provide one of the most valuable fisheries on the West Coast, a group of researchers has been figuring out how the crabs are likely to fare in a future Puget Sound. One study at NOAA’s Mukilteo Field Station near Everett began by hatching out some 6,000 crabs and exposing them to varying conditions, such as different levels of oxygen, carbon dioxide and temperature.

A Dungeness crab moves through eelgrass at Golden Gardens in Seattle. Photo: JBrew (https://flic.kr/p/HyAALL)

A Dungeness crab moves through eelgrass at Golden Gardens in Seattle. Photo: JBrew (CC BY 2.0).

In the earliest larval stage, fewer of the crabs survived when exposed to higher-than-normal carbon dioxide levels, according to NOAA researcher Paul McElhany. Among the crabs that did survive, researchers noted a slowing of their development, he said.

In a related experiment, older juvenile crabs, which began their lives in the wild, seemed to be unaffected by higher CO2 levels, but more studies are needed to confirm this result, he said. Further experiments will examine how even older juveniles and adults in the population could be affected by ocean acidification.

By studying the metabolism of these crabs under varying conditions, the researchers are hoping to explain the physiological changes that Dungeness crabs go through and what it will mean to the future of the wild population, said Shelly Trigg, another NOAA and UW researcher. So far, lab experiments seem to show that low-oxygen conditions trigger more pronounced changes than higher levels of acidity alone, she said.

McElhany noted that populations of Dungeness crabs have dramatically declined in recent years in both South Puget Sound near Olympia and in Southern Hood Canal near Hoodsport — waters known to have high levels of carbon dioxide. Because of dwindling crab populations in those areas, sport and commercial crabbing has been closed, and crabbers are left wondering what the future may hold.

While it might be easy to pin the blame on high carbon dioxide and low oxygen, McElhany said one must be careful not to become fixated on a single possible cause. “There are a lot of things going on that may be a primary driver for this population, but CO2 is something we need to consider.”

Plankton and vegetation

At the bottom of the food web, supporting a multitude of life forms, are tiny plankton, made up of thousands of different oceanic species. They include plantlike phytoplankton, which get their energy directly from the sun, and zooplankton, which survive by eating other organisms. Some plankton, known as mixotrophs, can do both.

Ocean acidification can have profound effects on the growth and makeup of the entire planktonic community, thus influencing the success and survival of many higher animals. Since zooplankton include the larval stages of larger animals — such as oysters and crabs — harsh conditions can wipe out a portion of the population before the young ever reach maturity.

Krill and copepods under a microscope. Photo: Jeff Napp, NOAA/NMFS/AFSC (https://flic.kr/p/JSk2Pd)

Krill and copepods under a microscope. Photo: Jeff Napp, NOAA/NMFS/AFSC (CC BY 2.0)

Evelyn Lessard and her associates at the UW School of Oceanography keep watch on how the plankton are doing by examining water samples taken three times a year from 40 monitoring stations throughout Puget Sound. Populations of various species expand and contract, as conditions constantly change, month-to-month and year-to-year.

Species most likely to die or be impaired by ocean acidification are those that form shells or other calcium carbonate structures, including:

  • Pteropods and gastropods (sea snails), which offer a key food supply for fish;
  • shrimp, clams and oysters, which are economically valuable;
  • echinoderm larvae, including young sea stars and sea urchins;
  • krill, which feed whales, birds and fish; and
  • amphipods and copepods, tiny shrimplike creatures that also provide food for fish and other animals.

Plankton surveys of Puget Sound have revealed where all these creatures are found at different times of the year and under different conditions, as Lessard reported during the symposium. So far, even the most sensitive zooplankton have survived, she said, although their numbers may be diminished at certain times and in certain areas.

Meanwhile, a research group at the Washington State Department of Natural Resources has been monitoring nearshore conditions in Puget Sound since 2015 to detect any rapid or ongoing ecological changes.

Measurements of water chemistry, shellfish growth and eelgrass density are being collected at nine sites in Puget Sound plus Willapa Bay on the outer coast. By taking measurements inside and outside eelgrass beds, the researchers are hoping to determine if the aquatic plants can reduce the effects of ocean acidification by removing carbon dioxide from the water and adding oxygen through photosynthesis, according to a presentation by Mikah Horwith, coastal scientist with DNR.

A researcher monitors eelgrass characteristics of height, density, percent cover, flowering shoots, and biomass at the Padilla Bay Reserve. Photo: Elliot Banko, Ecology (https://flic.kr/p/GD3crN)

A researcher monitors eelgrass characteristics of height, density, percent cover, flowering shoots, and biomass at the Padilla Bay Reserve. Photo: Elliot Banko, Department of Ecology (CC BY 2.0)

At least in some eelgrass beds, oxygen levels were dramatically increased during summer daylight hours when photosynthesis was humming along. Over longer periods, however, no general patterns emerged to show how eelgrass might be influencing water chemistry.

Nevertheless, experiments with oysters planted both inside and outside of eelgrass beds seemed to show very real benefits from the vegetation. The experiments, which included commercially valuable Pacific oysters as well as native Olympia oysters, examined many factors, from biochemical makeup of the oysters to their shell structure.

“Really broadly speaking, for Olympia oysters we have seen a general pattern of enhanced growth inside of eelgrass,” Horwith said. “This is not a minor thing. Typically we have seen in 2016 and ’17 a boost of about 30 percent in the growth rate of oysters inside of sea grass.”

In 2018, with using a somewhat different approach, the researchers found no difference in growth inside and outside of eelgrass beds. But this year, using even more experimental sites, Olympia oysters within eelgrass beds are showing a clear pattern of more rapid growth.

Limited work with Pacific oysters has so far shown a pattern consistent with Olympia oysters. On the other hand, similar experiments with Manila clams showed unexplained reduced growth. For geoduck clams, no significant difference has been seen so far.

“This, to me, illustrates the importance of working species by species,” Horwith said. “Even in the same potentially functional group, there can be big differences in the way they interact with water chemistry.”

Environmental DNA

While many researchers are studying how individual species respond to ocean acidification, one group from the UW’s School of Marine and Environmental Affairs is using DNA to ask a different question.

“We go out into the world and ask ‘What’s there?’” says ecologist Ryan Kelly, whose work with other researchers involves a search for DNA that has dispersed through the environment. This approach is referred to as environmental DNA research, or eDNA for short.

“Every living thing has DNA and is leaving that DNA in the environment,” Kelly said, explaining the concept at the symposium. “Whether you are a many-celled porpoise or a single-celled dinoflagellate, you have DNA, and so we can go and collect that.”

Simply put, researchers filter samples of water and run genetic tests to see which species have left their DNA behind. The results provide a good idea of what is living in a given area — and what is not.

In eDNA studies in Hood Canal and the San Juan Islands, more than 400 different kinds of plankton were found throughout the year. An analysis led by Ramòn Gallego in Kelly’s lab helped to reveal which plankton — including harmful species — showed up under various water conditions and where they were likely to appear at different times of the year.

An alternative approach in studying eDNA is to focus on a single species to see how the concentration of DNA differs from place to place or over time in one location. Conditions may dictate whether one place is more hospitable to a species than another or whether the species might do better in summer or winter.

Kelly showed his audience an animated map of Puget Sound, which changed to reveal monthly variations in the relative populations of Alexandrium, a toxic plankton responsible for paralytic shellfish poison, which can deadly to humans. During August 2017, high levels of DNA from Alexandrium suggested that a plankton bloom was underway in southern Hood Canal near Hoodsport.

In another study in Kelly’s lab, Kelly Cribari discovered quantities of DNA related to a group of plankton called Kareniaceae, which has been identified by other researchers as new potentially toxic algae. While nearly absent in waters with normal acidity, the species has been found in large numbers in areas with low pH. These new findings suggest that these plankton could become a growing problem in Puget Sound as ocean acidification intensifies.

Predicting future damage

Extensive monitoring of Puget Sound waters provides a fairly up-to-date picture of water conditions, such as temperature, dissolved oxygen, acidity and so on. But these numbers alone don’t describe the potential for damage that occurs to marine life when water quality gets out of whack.

Now, thanks to a team of scientists focused on biological effects, red flags can be raised to signal serious problems for certain organisms when water-quality measurements reach dangerous thresholds. The team is led by Nina Bednaršek, senior scientist at the Southern California Coastal Water Research Project, who presented the latest threshold findings during the ocean acidification symposium.

The first thresholds to be developed involved pteropods, a group of sea snails. These tiny animals are an important food source for many marine species, and they have been studied extensively for their sensitivity to ocean acidification. Specifically, their shells, which are made of calcium carbonate, do not grow properly in waters with low carbonate ion concentrations — so water chemistry becomes a life-or-death matter.

Besides a low concentration of carbonate, the time of exposure in corrosive waters can affect the severity of damage. The new thresholds include both concentration and duration factors. For example, pteropod eggs may fail to develop in water low in carbonate — even when the exposure is just two days. On the other hand, pteropod adults are likely to survive longer in the same water, perhaps because their shells are already complete. Studies have identified threshold levels for mild and severe shell dissolution, as well as other negative biological responses.

Published thresholds — which include levels of magnitude and duration — have been derived through a consensus of a dozen or more experts familiar with ocean acidification effects on specific species. Besides pteropods, thresholds have been developed — but not yet reported — for echinoderms, such as sea stars and sea urchins. Thresholds for Dungeness crabs are under development.

When combined with real-time temperature and chemical data gathered from monitoring buoys and other sources, one can get an understanding of the type of damage taking place over time. Bednaršek said conditions in Puget Sound often reach harmful levels for all ages of pteropods, especially in Hood Canal, South Sound and Whidbey Basin.

One can also combine predictive models with biological thresholds to anticipate problems for specific species. For example, the Salish Sea Model, under development by the Washington Department of Ecology, is designed to predict water chemistry based on a number of factors — including the amount of natural and human sources of nutrients coming into Puget Sound.

Based on that modeling, excess nutrients — such as nitrogen from sewage-treatment plants — were found to contribute significantly to water conditions that caused thresholds to be exceeded for pteropods and larval Dungeness crabs. Some of the greatest nutrient problems contributing to threshold exceedance were seen in Hood Canal, South Puget Sound and Whidbey Basin.

Thresholds for Dungeness crabs and other commercial species could be used in the future to help estimate economic losses from ocean acidification, whether caused by nutrient loading or atmospheric deposition.

A different kind of predictive model discussed at the symposium, called LiveOcean, is designed to produce daily forecasts of underwater conditions likely to occur over the coming three days. Similar to a weather forecast, the model uses up-to-date information on currents and other physical and chemical properties to predict changes in water conditions in the Salish Sea and along the coast.

LiveOcean can predict when and where pH will dip to dangerous levels, the potential course of toxic algae blooms, and likely pathways for incursions of aquatic invasive species, such as European green crabs, according to UW oceanographer Parker MacReady, who led the effort to develop the model.

One of its most important applications — and the initial motivation for building the model — is to help shellfish growers avoid deadly waters when planting oyster seed and operating oyster hatcheries, MacReady explained.

Oceanographer Samantha Siedlecki reported on an analysis that looked out to the year 2100, showing that many ocean conditions along the West Coast are likely to become more severe — more harmful to sea life — than predicted by global models.

The analysis, which involved numerous collaborators, considered how local factors — such coastal currents, upwelling and biological activity — tend to “amplify” projections developed at a global scale, said Siedlecki, a former UW research scientist now based at the University of Connecticut.

While the new analysis showed a rate of acidification fairly consistent with global models, levels of temperature and carbon dioxide are projected to be adversely higher in the year 2100 — much higher in some areas. Likewise, beneficial oxygen and calcium carbonate levels are predicted to be lower than global projections would suggest, and the amount of time that dangerous low-oxygen levels are present could double by 2100 in several coastal areas.

Moderator Jan Newton, a UW oceanographer, said it was important to recognize the capabilities of experts in this region who are developing “really sophisticated hydrodynamic models” to calculate future ocean conditions.

“I really want to acknowledge the groundbreaking that is going on here, and thank you all,” she said.

State policies and communication

Ocean acidification can be a daunting problem for scientists, politicians and the public, but Washington state has always stepped up to the challenge, according to Jennifer Hennessey, oceans policy adviser to Gov. Jay Inslee.

In 2012, she said, Washington was one of the first states to address the problem of ocean acidification with the release of a comprehensive plan containing six broad strategies:

  1. Reduce carbon emissions, such as from power generation and transportation, while improving energy efficiency,
  2.  Reduce land-based contributions to ocean acidification, such as from sewage systems, agriculture and development,
  3. Increase adaptation to change, such as by restoring shoreline habitats, recycling seaweed for upland uses and propagating native species to maintain biodiversity,
  4. Invest in science to enhance understanding and reveal new approaches to the problem,
  5. Inform and engage stakeholders, leaders and the public, and
  6. Maintain a sustainable focus on ocean acidification through policy and science coordination.

“Washington’s strategy catalyzed ingenuity across the state and partnerships up and down the West Coast,” Hennessey said during the symposium. “The state has invested millions in ocean acidification work. We’ve leveraged federal resources that are here — we are very lucky to have them here — and we have attracted private financing, too.”

Progress has been made on all six of those fronts, as identified in a 2017 update by the Marine Resources Advisory Council, she said. And this year the state took a big step forward when the Legislature doubled the state’s investment in ocean acidification — including money for a variety of scientific studies. Lawmakers also approved a package of governor-proposed initiatives, including mandates requiring only renewable energy supplies by 2045 along with new building-efficiency standards.

“Our action plan is held up as an example of how to move from a problem to action,” Hennessey said, adding that Washington is collaborating with other states, including Oregon and California. Those states were represented at the symposium by Steve Weisberg of the Southern California Coastal Water Research Project and Charlotte Whitefield of the Oregon Coordinating Council on Ocean Acidification and Hypoxia. Both Weisberg and Whitefield said their states are working from action plans similar to Washington’s.

“We are elevating this issue through various forums, including the launch of the International Alliance to Combat Ocean Acidification,” Hennessey said.

She noted that the organization has grown to more than 80 members —including 10 states and provinces, 12 nations, seven tribes and four cities, plus dozens of businesses and nonprofit groups along with educational and research institutions.

“Our partnerships are playing an important role, but we need to do more,” Hennessey said. “We need to expand the breadth and depth of those partnerships, and we need to get beyond the usual circle of people in this room.

“We need to connect with people first. Why should they care? We need to make it relevant to the audience … and we need to identify actions,” she continued. “Without this connection, people are left wondering what they should do and feeling somewhat helpless with those curves (on graphs) that Dick (Feely) started us off with early in the day.”

Moderator Jan Newton said she thought she heard gasps in the room when Feely outlined the frightening path forward, as ocean acidification picks up its pace because of changes in ocean chemistry.

“We are understanding so much more and becoming more sophisticated about this issue,” Newton said. “As much as we are captive to our science, we have a huge responsibility here, and that gets to the point of communication. We get excited when one agency works with another agency, but we have to go way beyond that.”

Communication with the public, she concluded, is being planned to outline the problem in some detail and gain momentum for a different path to the future.


About the author: Christopher Dunagan is a senior writer at the Puget Sound Institute.