By Devon Merriman
Some think of climate change as a crisis we will face in the future, but the shellfish industry and the organisms they depend on have already been feeling the effects. Shellfish farmers have witnessed mass die-offs of oyster larvae, with many concluding that at least part of the reason is that the ocean is increasing in acidity. But oyster babies aren’t the only ones who could be impacted, as changes in ocean water could be a threat to other sea creatures as well. Scientists at Evergreen, and around the world, are studying marine organisms to predict how ocean ecosystems will be affected.
Next to melting ice caps, ocean acidification is another major threat posed by carbon dioxide emissions. Die-offs of shellfish are one impact of this phenomenon. Although hatchery oysters grow in artificial settings, seawater is used in their environment. Because the oceans naturally absorb CO2, its waters are becoming increasingly acidic, compromising the strength of their shells.
“This makes them more vulnerable to predators,” said Pauline Yu, a biology professor at the Evergreen State College. “But there’s also the success rate. If the babies don’t develop properly, chances are they won’t be able to metamorphose into adults.” This is obviously bad news for the shellfish industry, which contributes around $270 million a year to the Pacific Northwest economy.
The dissolution of CO2 into the ocean leads to the release of hydrogen ions, which make the ocean more acidic. This addition can be especially damaging along the coast of the Pacific Northwest, where it can intensify upwellings. Upwellings are natural acidification events in which surface waters are blown toward the middle of the ocean and the deeper, colder, and more acidic waters surge up to replace it.
Some marine organisms struggle to survive in this more acidic environment, particularly those with shells made of calcium carbonate. Oysters, some plankton, and even our own mascot, the geoduck, have calcium carbonate shells that are potentially threatened by rising ocean acidity. These organisms need carbonate ions to build their shells, but since carbonate ions are negatively charged and hydrogen ions are positively charged, the hydrogen ions are attracted and bind to them, “stealing” the carbonate ions from the shellfish. Since the ingredients to build their shells are not available, these organisms end up with weaker ones. And even after their shells are built, the extra hydrogen ions floating around in the water can still dissolve them, further weakening their shells and lowering their life spans. Because these calcified invertebrates serve as food for many other marine organisms, scientists fear that die-offs could move up the food chain, affecting much more than just the shellfish industry.
Nevertheless, farmers and scientists have worked together to figure out ways to mitigate the effects. Taylor Shellfish Farms, Inc. is the biggest shellfish producer in the U.S., and since 2013, they have been treating their water with sodium carbonate before it reaches their oyster larvae. By adding carbonate to the water, the oysters have enough for their shells before they are set into the natural environment. So far, the larvae have been doing well. But this doesn’t mean the battle is won. “As conditions get worse in the coming years, the animals that are doing okay right now (that are in the bay where we don’t treat the water) might not be okay in ten years or so,” said Benoit Eudeline, a researcher for Taylor Shellfish. “We seem to have some control over the hatchery conditions, but we have no control over the bay, so it’s very worrying what might come next.”
Researching Animals
In response to the threat, scientists are gathering knowledge about this issue and testing solutions around the globe. Biologists are investigating the effects on organisms with calcium carbonate shells. One of these biologists is Evergreen professor Pauline Yu.
Before becoming a professor, Yu studied sea urchins at the University of California at Berkeley. “Like oysters and clams, sea urchins also have calcified parts [made of calcium carbonate]. Superficially, sea urchins look like their skeleton is on the outside, but it’s actually covered by a really thin layer of skin, so it’s technically an endoskeleton, like ours.”
But that layer of skin isn’t enough to protect sea urchins from acidification. Their skin is permeable, allowing hydrogen ions to pass through and dissolve their skeletons.
In her study, Yu collected urchins from the coast of California and combined their eggs and sperm to create embryos. These sea urchin embryos were placed in a special flow-through aquarium with a valve that can adjust the level of CO2 going through it very precisely. Some developing sea urchins were exposed to the high levels of CO2 expected in the future, while the control group lived in waters that resembled current conditions.
“We found that sea urchins, to some extent, could tolerate pretty high levels of CO2,” said Yu. “A fair number of sea urchins survived, however their skeletons were definitely smaller by around 10 to 15 percent.”
Research at Evergreen
Evergreen students are also interested in studying the possible repercussions of acidification.
Derek King, an alumni of Evergreen, is one of the founders of the Evergreen Shellfish Club. While he was an undergrad, he did research on how ocean acidification could possibly affect a predator of shellfish, an invasive species of snail called the Japanese oyster drill.
“They will actually drill into the oyster using a kind of mechanical or acid drilling, and eat the meat side.” King said. “I was curious in my research whether the drills would be more efficient in an acidic situation.”
He explained that his results were inconclusive due to small sample size and losses, but with what he had, he ended up finding that the drills were not as successful. “I can’t say one way or another, but these animals have an ability to really understand their environment through smell and it’s possible that in a more acidic situation, those animals might have a harder time distinguishing between those smells.”
“Students who have carried out ocean acidification projects have learned a huge amount. They have to learn a lot of different skills and techniques,” said Erik Thuesen, a biology professor at Evergreen. However, there are several difficulties that arise if you’re an Evergreen undergraduate wanting to study ocean acidification. One hurdle is the time constraints you have as an undergraduate. Many projects need to be finished within 3 months, which, on a biological standpoint, is pretty short. Graduate students, on the other hand, have the time to focus and invest the energy required to do these time-consuming experiments.
Another problem is that the equipment to make these projects easier to conduct is not available at Evergreen, specifically the Coulometer for Total Inorganic Carbon in seawater. First, someone would need to find a technician who can take care of it and who can teach students how to use it. The instrument would also be hard to maintain due to the changing nature of Evergreen’s system: the classes available change from year to year. “The equipment itself is not that expensive,” said Thuesen. “If we had enough people devoted to doing that then I think we could get it. But its hard to justify when you are only going to use it every other year.”
Although it is difficult at Evergreen to carry out a publishable paper on ocean acidification, Yu hopes that once she gets her lab set up this summer, she could incorporate some local projects into future marine science curricula.
There are still many unanswered questions on ocean acidification. A big challenge is designing realistic experiments that combine other factors, like warming temperatures of the oceans, along with the acidification component. There are also studies of plants that could help coastal oceans by taking the CO2 out of the water with photosynthesis, like seagrass and seaweed. But the most effective solution, of course, is to cut down on human-caused CO2 emissions.
