Actual Effects on the Ocean:
The pH of the ocean fluctuates within limits as a result of natural processes, and ocean organisms are well-adapted to survive the changes that they normally experience. Some marine species may be able to adapt to more extreme changes—but many will suffer, and there will likely be extinctions. We can't know this for sure, but during the last great acidification event 55 million years ago, there were mass extinctions in some species including deep sea invertebrates. A more acidic ocean won’t destroy all marine life in the sea, but the rise in seawater acidity of 30 percent that we have already seen is already affecting some ocean organisms.
Coral Reefs:
Branching corals, because of their more fragile structure, struggle to live in acidified waters around natural carbon dioxide seeps, a model for a more acidic future ocean.
Reef-building corals craft their own homes from calcium carbonate, forming complex reefs that house the coral animals themselves and provide habitat for many other organisms. Acidification may limit coral growth by corroding pre-existing coral skeletons while simultaneously slowing the growth of new ones, and the weaker reefs that result will be more vulnerable to erosion. This erosion will come not only from storm waves, but also from animals that drill into or eat coral. By the middle of the century, it’s possible that even otherwise healthy coral reefs will be eroding more quickly than they can rebuild.
Acidification may also impact corals before they even begin constructing their homes. The eggs and larvae of only a few coral species have been studied, and more acidic water didn’t hurt their development while they were still in the plankton. However, larvae in acidic water had more trouble finding a good place to settle, preventing them from reaching adulthood.
How much trouble corals run into will vary by species. Some types of coral can use bicarbonate instead of carbonate ions to build their skeletons, which gives them more options in an acidifying ocean. Some can survive without a skeleton and return to normal skeleton-building activities once the water returns to a more comfortable pH. Others can handle a wider pH range.
Reef-building corals craft their own homes from calcium carbonate, forming complex reefs that house the coral animals themselves and provide habitat for many other organisms. Acidification may limit coral growth by corroding pre-existing coral skeletons while simultaneously slowing the growth of new ones, and the weaker reefs that result will be more vulnerable to erosion. This erosion will come not only from storm waves, but also from animals that drill into or eat coral. By the middle of the century, it’s possible that even otherwise healthy coral reefs will be eroding more quickly than they can rebuild.
Acidification may also impact corals before they even begin constructing their homes. The eggs and larvae of only a few coral species have been studied, and more acidic water didn’t hurt their development while they were still in the plankton. However, larvae in acidic water had more trouble finding a good place to settle, preventing them from reaching adulthood.
How much trouble corals run into will vary by species. Some types of coral can use bicarbonate instead of carbonate ions to build their skeletons, which gives them more options in an acidifying ocean. Some can survive without a skeleton and return to normal skeleton-building activities once the water returns to a more comfortable pH. Others can handle a wider pH range.
Close to the volcanic CO2 seeps, the vast diversity of corals that exists in less-acidic waters is replaced by a "monoculture" of boulder corals.
Nonetheless, in the next century we will see the common types of coral found in reefs shifting—though we can't be entirely certain what that change will look like. On reefs in Papua New Guinea that are affected by natural carbon dioxide seeps, big boulder colonies have taken over and the delicately branching forms have disappeared, probably because their thin branches are more susceptible to dissolving. This change is also likely to affect the many thousands of organisms that live among the coral, including those that people fish and eat, in unpredictable ways. In addition, acidification gets piled on top of all the other stresses that reefs have been suffering from, such as warming water (which causes another threat to reefs known as coral bleaching), pollution, and overfishing.
Nonetheless, in the next century we will see the common types of coral found in reefs shifting—though we can't be entirely certain what that change will look like. On reefs in Papua New Guinea that are affected by natural carbon dioxide seeps, big boulder colonies have taken over and the delicately branching forms have disappeared, probably because their thin branches are more susceptible to dissolving. This change is also likely to affect the many thousands of organisms that live among the coral, including those that people fish and eat, in unpredictable ways. In addition, acidification gets piled on top of all the other stresses that reefs have been suffering from, such as warming water (which causes another threat to reefs known as coral bleaching), pollution, and overfishing.
Oysters, Mussels, Urchins and Starfish:
Ochre seastars (Pisaster ochraceus) feed on mussels off the coast of Oregon.
Generally, shelled animals—including mussels, clams, urchins and starfish—are going to have trouble building their shells in more acidic water, just like the corals. Mussels and oysters are expected to grow less shell by 25 percent and 10 percent respectively by the end of the century. Urchins and starfish aren’t as well studied, but they build their shell-like parts from high-magnesium calcite, a type of calcium carbonate that dissolves even more quickly than the aragonite form of calcium carbonate that corals use. This means a weaker shell for these organisms, increasing the chance of being crushed or eaten.
Some of the major impacts on these organisms go beyond adult shell-building, however. Mussels’ byssal threads, with which they famously cling to rocks in the pounding surf, can’t hold on as well in acidic water. Meanwhile, oyster larvae fail to even begin growing their shells. In their first 48 hours of life, oyster larvae undergo a massive growth spurt, building their shells quickly so they can start feeding. But the more acidic seawater eats away at their shells before they can form; this has already caused massive oyster die-offs in the U.S. Pacific Northwest.
This massive failure isn’t universal, however: studies have found that crustaceans (such as lobsters, crabs, and shrimp) grow even stronger shells under higher acidity. This may be because their shells are constructed differently. Additionally, some species may have already adapted to higher acidity or have the ability to do so, such as purple sea urchins. (Although a new study found that larval urchins have trouble digesting their food under raised acidity.)
Of course, the loss of these organisms would have much larger effects in the food chain, as they are food and habitat for many other animals.
Generally, shelled animals—including mussels, clams, urchins and starfish—are going to have trouble building their shells in more acidic water, just like the corals. Mussels and oysters are expected to grow less shell by 25 percent and 10 percent respectively by the end of the century. Urchins and starfish aren’t as well studied, but they build their shell-like parts from high-magnesium calcite, a type of calcium carbonate that dissolves even more quickly than the aragonite form of calcium carbonate that corals use. This means a weaker shell for these organisms, increasing the chance of being crushed or eaten.
Some of the major impacts on these organisms go beyond adult shell-building, however. Mussels’ byssal threads, with which they famously cling to rocks in the pounding surf, can’t hold on as well in acidic water. Meanwhile, oyster larvae fail to even begin growing their shells. In their first 48 hours of life, oyster larvae undergo a massive growth spurt, building their shells quickly so they can start feeding. But the more acidic seawater eats away at their shells before they can form; this has already caused massive oyster die-offs in the U.S. Pacific Northwest.
This massive failure isn’t universal, however: studies have found that crustaceans (such as lobsters, crabs, and shrimp) grow even stronger shells under higher acidity. This may be because their shells are constructed differently. Additionally, some species may have already adapted to higher acidity or have the ability to do so, such as purple sea urchins. (Although a new study found that larval urchins have trouble digesting their food under raised acidity.)
Of course, the loss of these organisms would have much larger effects in the food chain, as they are food and habitat for many other animals.
Zooplankton:
This pair of sea butterflies (Limacina helicina) flutter not far from the ocean's surface in the Arctic.
There are two major types of zooplankton (tiny drifting animals) that build shells made of calcium carbonate: foraminifera and pteropods. They may be small, but they are big players in the food webs of the ocean, as almost all larger life eats zooplankton or other animals that eat zooplankton. They are also critical to the carbon cycle—how carbon (as carbon dioxide and calcium carbonate) moves between air, land and sea. Oceans contain the greatest amount of actively cycled carbon in the world and are also very important in storing carbon. When shelled zooplankton (as well as shelled phytoplankton) die and sink to the seafloor, they carry their calcium carbonate shells with them, which are deposited as rock or sediment and stored for the foreseeable future. This is an important way that carbon dioxide is removed from the atmosphere, slowing the rise in temperature caused by the greenhouse effect.
These tiny organisms reproduce so quickly that they may be able to adapt to acidity better than large, slow-reproducing animals. However, experiments in the lab and at carbon dioxide seeps (where pH is naturally low) have found that foraminifera do not handle higher acidity very well, as their shells dissolve rapidly. One study even predicts that foraminifera from tropical areas will be extinct by the end of the century.
The shells of pteropods are already dissolving in the Southern Ocean, where more acidic water from the deep sea rises to the surface, hastening the effects of acidification caused by human-derived carbon dioxide. Like corals, these sea snails are particularly susceptible because their shells are made of aragonite, a delicate form of calcium carbonate that is 50 percent more soluble in seawater.
One big unknown is whether acidification will affect jellyfish populations. In this case, the fear is that they will survive unharmed. Jellyfish compete with fish and other predators for food—mainly smaller zooplankton—and they also eat young fish themselves. If jellyfish thrive under warm and more acidic conditions while most other organisms suffer, it’s possible that jellies will dominate some ecosystems (a problem already seen in parts of the ocean).
There are two major types of zooplankton (tiny drifting animals) that build shells made of calcium carbonate: foraminifera and pteropods. They may be small, but they are big players in the food webs of the ocean, as almost all larger life eats zooplankton or other animals that eat zooplankton. They are also critical to the carbon cycle—how carbon (as carbon dioxide and calcium carbonate) moves between air, land and sea. Oceans contain the greatest amount of actively cycled carbon in the world and are also very important in storing carbon. When shelled zooplankton (as well as shelled phytoplankton) die and sink to the seafloor, they carry their calcium carbonate shells with them, which are deposited as rock or sediment and stored for the foreseeable future. This is an important way that carbon dioxide is removed from the atmosphere, slowing the rise in temperature caused by the greenhouse effect.
These tiny organisms reproduce so quickly that they may be able to adapt to acidity better than large, slow-reproducing animals. However, experiments in the lab and at carbon dioxide seeps (where pH is naturally low) have found that foraminifera do not handle higher acidity very well, as their shells dissolve rapidly. One study even predicts that foraminifera from tropical areas will be extinct by the end of the century.
The shells of pteropods are already dissolving in the Southern Ocean, where more acidic water from the deep sea rises to the surface, hastening the effects of acidification caused by human-derived carbon dioxide. Like corals, these sea snails are particularly susceptible because their shells are made of aragonite, a delicate form of calcium carbonate that is 50 percent more soluble in seawater.
One big unknown is whether acidification will affect jellyfish populations. In this case, the fear is that they will survive unharmed. Jellyfish compete with fish and other predators for food—mainly smaller zooplankton—and they also eat young fish themselves. If jellyfish thrive under warm and more acidic conditions while most other organisms suffer, it’s possible that jellies will dominate some ecosystems (a problem already seen in parts of the ocean).
Plants and Algae:
Neptune grass (Posidonia oceanica) is a slow-growing and long-lived seagrass native to the Mediterranean.
Plants and many algae may thrive under acidic conditions. These organisms make their energy from combining sunlight and carbon dioxide—so more carbon dioxide in the water doesn't hurt them, but helps.
Seagrasses form shallow-water ecosystems along coasts that serve as nurseries for many larger fish, and can be home to thousands of different organisms. Under more acidic lab conditions, they were able to reproduce better, grow taller, and grow deeper roots—all good things. However, they are in decline for a number of other reasons—especially pollution flowing into coastal seawater—and it's unlikely that this boost from acidification will compensate entirely for losses caused by these other stresses.
Some species of algae grow better under more acidic conditions with the boost in carbon dioxide. But coralline algae, which build calcium carbonate skeletons and help cement coral reefs, do not fare so well. Most coralline algae species build shells from the high-magnesium calcite form of calcium carbonate, which is more soluble than the aragonite or regular calcite forms. One studyfound that, in acidifying conditions, coralline algae covered 92 percent less area, making space for other types of non-calcifying algae, which can smother and damage coral reefs. This is doubly bad because many coral larvae prefer to settle onto coralline algae when they are ready to leave the plankton stage and start life on a coral reef.
One major group of phytoplankton (single celled algae that float and grow in surface waters), the coccolithophores, grows shells. Early studies found that, like other shelled animals, their shells weakened, making them susceptible to damage. But a longer-term study let a common coccolithophore (Emiliania huxleyi) reproduce for 700 generations, taking about 12 full months, in the warmer and more acidic conditions expected to become reality in 100 years. The population was able to adapt, growing strong shells. It could be that they just needed more time to adapt, or that adaptation varies species by species or even population by population.
Plants and many algae may thrive under acidic conditions. These organisms make their energy from combining sunlight and carbon dioxide—so more carbon dioxide in the water doesn't hurt them, but helps.
Seagrasses form shallow-water ecosystems along coasts that serve as nurseries for many larger fish, and can be home to thousands of different organisms. Under more acidic lab conditions, they were able to reproduce better, grow taller, and grow deeper roots—all good things. However, they are in decline for a number of other reasons—especially pollution flowing into coastal seawater—and it's unlikely that this boost from acidification will compensate entirely for losses caused by these other stresses.
Some species of algae grow better under more acidic conditions with the boost in carbon dioxide. But coralline algae, which build calcium carbonate skeletons and help cement coral reefs, do not fare so well. Most coralline algae species build shells from the high-magnesium calcite form of calcium carbonate, which is more soluble than the aragonite or regular calcite forms. One studyfound that, in acidifying conditions, coralline algae covered 92 percent less area, making space for other types of non-calcifying algae, which can smother and damage coral reefs. This is doubly bad because many coral larvae prefer to settle onto coralline algae when they are ready to leave the plankton stage and start life on a coral reef.
One major group of phytoplankton (single celled algae that float and grow in surface waters), the coccolithophores, grows shells. Early studies found that, like other shelled animals, their shells weakened, making them susceptible to damage. But a longer-term study let a common coccolithophore (Emiliania huxleyi) reproduce for 700 generations, taking about 12 full months, in the warmer and more acidic conditions expected to become reality in 100 years. The population was able to adapt, growing strong shells. It could be that they just needed more time to adapt, or that adaptation varies species by species or even population by population.
Fish:
Two bright orange anemonefish poke their heads between anemone tentacles.
While fish don't have shells, they will still feel the effects of acidification. Because the surrounding water has a lower pH, a fish's cells often come into balance with the seawater by taking in carbonic acid. This changes the pH of the fish's blood, a condition called acidosis.
Although the fish is then in harmony with its environment, many of the chemical reactions that take place in its body can be altered. Just a small change in pH can make a huge difference in survival. In humans, for instance, a drop in blood pH of 0.2-0.3 can cause seizures, comas, and even death. Likewise, a fish is also sensitive to pH and has to put its body into overdrive to bring its chemistry back to normal. To do so, it will burn extra energy to excrete the excess acid out of its blood through its gills, kidneys and intestines. It might not seem like this would use a lot of energy, but even a slight increase reduces the energy a fish has to take care of other tasks, such as digesting food, swimming rapidly to escape predators or catch food, and reproducing. It can also slow fishes growth.
Even slightly more acidic water may also affects fishes' minds. While clownfish can normally hear and avoid noisy predators, in more acidic water, they do not flee threatening noise. Clownfish also stray farther from home and have trouble "smelling" their way back. This may happen because acidification, which changes the pH of a fish's body and brain, could alter how the brain processes information. Additionally, cobia (a kind of popular game fish) grow larger otoliths—small ear bones that affect hearing and balance—in more acidic water, which could affect their ability to navigate and avoid prey. While there is still a lot to learn, these findings suggest that we may see unpredictable changes in animal behavior under acidification.
The ability to adapt to higher acidity will vary from fish species to fish species, and what qualities will help or hurt a given fish species is unknown. A shift in dominant fish species could have major impacts on the food web and on human fisheries.
While fish don't have shells, they will still feel the effects of acidification. Because the surrounding water has a lower pH, a fish's cells often come into balance with the seawater by taking in carbonic acid. This changes the pH of the fish's blood, a condition called acidosis.
Although the fish is then in harmony with its environment, many of the chemical reactions that take place in its body can be altered. Just a small change in pH can make a huge difference in survival. In humans, for instance, a drop in blood pH of 0.2-0.3 can cause seizures, comas, and even death. Likewise, a fish is also sensitive to pH and has to put its body into overdrive to bring its chemistry back to normal. To do so, it will burn extra energy to excrete the excess acid out of its blood through its gills, kidneys and intestines. It might not seem like this would use a lot of energy, but even a slight increase reduces the energy a fish has to take care of other tasks, such as digesting food, swimming rapidly to escape predators or catch food, and reproducing. It can also slow fishes growth.
Even slightly more acidic water may also affects fishes' minds. While clownfish can normally hear and avoid noisy predators, in more acidic water, they do not flee threatening noise. Clownfish also stray farther from home and have trouble "smelling" their way back. This may happen because acidification, which changes the pH of a fish's body and brain, could alter how the brain processes information. Additionally, cobia (a kind of popular game fish) grow larger otoliths—small ear bones that affect hearing and balance—in more acidic water, which could affect their ability to navigate and avoid prey. While there is still a lot to learn, these findings suggest that we may see unpredictable changes in animal behavior under acidification.
The ability to adapt to higher acidity will vary from fish species to fish species, and what qualities will help or hurt a given fish species is unknown. A shift in dominant fish species could have major impacts on the food web and on human fisheries.
Climatic Effects:
Polar bear on a remnant ice floe: Credit: Gerard Van der Leun at Flickr.
As predicted by chemistry, change in the Arctic Ocean is accelerating as temperatures warm faster than the global average, as the sea ice melts, as northern rivers run stronger and faster, delivering more fresh water farther into the northernmost ocean, and as we continue blasting an ever increasing quantity of greenhouse gases into the atmosphere. The Arctic Ocean Acidification Assessment, a new report from the Arctic Monitoring and Assessment Program (AMAP), presents these 10 key findings:
As predicted by chemistry, change in the Arctic Ocean is accelerating as temperatures warm faster than the global average, as the sea ice melts, as northern rivers run stronger and faster, delivering more fresh water farther into the northernmost ocean, and as we continue blasting an ever increasing quantity of greenhouse gases into the atmosphere. The Arctic Ocean Acidification Assessment, a new report from the Arctic Monitoring and Assessment Program (AMAP), presents these 10 key findings:
1. Arctic marine waters are experiencing widespread and rapid ocean acidification. In the Nordic Seas, acidification is taking place over a wide range of ocean depths, from surface waters (faster) to deep waters (more slowly). Seawater pH has declined ~0.02 per decade since the late 1960s in the Iceland and Barents Seas. Other ocean acidification signals have also been encountered in surface waters of the Bering Strait and the Canada Basin of the central Arctic Ocean.
US Geological Survey at Flickr
2. The primary driver of ocean acidification is uptake of carbon dioxide emitted to the atmosphere by human activities. The ocean has swallowed our atmospheric carbon dioxide emissions and slowed global warming during the past few critical decades while we dithered in disbelief. But the cost of temporarily delaying even more warming has been the increasing acidification of seawater. The average acidity of surface ocean waters worldwide is now ~30% higher than at the start of the Industrial Revolution.
US Geological Survey at Flickr
3. The Arctic Ocean is especially vulnerable to ocean acidification. Arctic rivers plus melting ice input huge (and increasing) amounts of freshwater into the Arctic Ocean, changing the chemistry and making it less effective at neutralizing CO2's acidifying effects. Add the fact that cold waters slurp up more CO2 from the air. Add the fact that dramatic decreases in Arctic summer sea-ice cover—real and projected—allow for greater transfer of CO2 from the atmosphere into the ocean. These combined influences make Arctic waters among the world's most easily acidified.
US Geological Survey at Flickr
4. Acidification is not uniform across the Arctic Ocean. Other processes influence the pace and extent of ocean acidification. Rivers, sea-floor sediments, and coastal erosion all supply organic material that bacteria can convert to carbon dioxide, exacerbating ocean acidification, especially on shallow continental shelves. Sea-ice cover, freshwater inputs, and plant growth and decay also influence local ocean acidification. The contributions of these processes vary from place to place, season to season, and year to year. The result is a complex, unevenly distributed, ever-changing mosaic of Arctic acidification states.
Brian Gratwicke at Flickr
5. Arctic marine ecosystems are highly likely to undergo significant change due to ocean acidification. Arctic marine ecosystems are generally characterized by short, simple food webs, where energy is channeled in just a few steps from small plants and animals to large predators like seabirds and seals. The integrity of such a simple structure depends greatly on keystone species. Pteropods (sea butterflies) and echinoderms (sea stars, urchins) are key food-web organisms that may be sensitive to ocean acidification. Too few data are presently available to assess the precise nature and extent of Arctic ecosystem vulnerability, as most biological studies have been undertaken in other ocean regions. Arctic-specific long-term studies are urgently needed.
US Geological Survey at Flick
6. Ocean acidification will have direct and indirect effects on arctic marine life.Some marine organisms will respond positively to new conditions associated with ocean acidification. Others won't. Experiments show that a wide variety of animals grow more slowly under the acidification levels projected for coming centuries. While some seagrasses appear to thrive under such conditions. Birds and mammals are not likely to be directly affected by acidification but may be indirectly affected if their food sources decline, expand, relocate, or otherwise change in response to ocean acidification. Ocean acidification may alter the extent to which nutrients and essential trace elements in seawater are available to marine organisms. Shell-building Arctic mollusks are likely to be negatively affected by acidification, especially at early life stages. Juvenile and adult fishes are thought likely to cope with acidification levels projected for the next century, but fish eggs and early larval stages may be more sensitive. In general, early life stages are more susceptible to direct effects of ocean acidification than later life stages.
US Geological Survey at Flick
7. Ocean acidification impacts must be assessed in the context of other changes happening in Arctic waters. Arctic marine organisms are experiencing not only acidification but also other large simultaneous changes: climate change, harvesting, habitat degradation, and pollution. Ecological interactions—e.g. between predators and prey, or among competitors—also play an important role in shaping ocean communities. As different marine life responds to environmental change in different ways, the mix of plants and animals in a community will change, as will their interactions with each other. We don't know much of anything about this yet.
NOAA Photo Library at Flick
8. Ocean acidification is one of several factors that may contribute to alteration of fish species' composition in the Arctic Ocean. Ocean acidification is likely to affect the abundance, productivity, and distribution of marine species. But the magnitude and direction of change are uncertain. Other processes driving Arctic change include rising temperatures, diminishing sea ice, and freshening surface waters.
Western Arctic National Parklands at Flick
9. Ocean acidification may affect Arctic fisheries. Few studies have estimated the socio-economic impacts of ocean acidification on fisheries, and most have focused largely on shellfish and on regions outside the Arctic. The quantity, quality, and predictability of commercially important Arctic fish stocks may be affected by ocean acidification, but the magnitude and direction of change are uncertain. Fish stocks may be more robust to ocean acidification if other stresses—for example, overfishing or habitat degradation—are minimized.
missmonet at Flickr
10. Ecosystem changes associated with ocean acidification may affect the livelihoods of Arctic peoples. Marine species harvested by northern coastal communities include species likely to be affected by acidification. Most indigenous groups harvest a range of organisms and may be able to shift to a greater reliance on unaffected species, but these changes would likely exert a cultural toll. Recreational fish catches may change to different species. While marine mammals—important to the culture, diets and livelihoods of Arctic indigenous peoples and other Arctic residents—are unlikely to escape changes in the Arctic Ocean food web.