Dungeness crabs are Shallin Busch’s lab rats in her research of ocean acidification.
Scientists have been studying the effects of carbon dioxide on climate for decades.
More recently, however, it was discovered that the oceans have absorbed about a third of the CO2 emitted into the atmosphere. Carbon dioxide alters ocean chemistry, making seawater more acidic. The scientific term for this phenomenon is “ocean acidification.”
Acidification threatens not only the ecological health of the oceans, but also the economic well-being of the communities and industries that depend on a productive marine environment.
It’s a powerful motivation for scientists, including Shallin Busch.
Dungeness crabs are her lab rats.
Shallin Busch is a Mukilteo-based ecologist whose research is linking ocean acidification to the deteriorating health of the Puget Sound ecosystem.
Busch, 40, has been a fisheries biologist and researcher for the National Oceanic & Atmospheric Administration’s Northwest Fisheries Science Center at Mukilteo for nearly 10 years. She is at the forefront of NOAA’s efforts to understand the effects of ocean acidification.
“I have just been driven by this question. How does our physiology change with our environment? I stumbled on that in college and I’ve been following it ever since,” she said. “Climate change and ocean acidification is really a huge threat to the Earth as we know it.”
After earning a doctorate in zoology at the University of Washington, Busch was hired to do fisheries research for NOAA.
Though she was stationed in Maryland for a year, the Mukilteo field station is her research home. Since 2014 she has worked for the Ocean Acidification Program, dedicating herself to understanding and predicting the threat acidification has on the West Coast’s food web and fishery management. She co-leads experiments at the research lab, which are carried out by a team of scientists.
“Ocean acidification is not part of climate change,” Busch said, but both problems are caused by carbon dioxide. “As we burn fossil fuels, more carbon dioxide is released into the atmosphere and dissolves into the ocean. It’s a chemical change that results in a drop in pH and an increase in acidity.”
The Mukilteo team has looked at or is looking at ocean acidification effects on krill, salmon, Dungeness crab, black cod and pteropod (marine snails). So far it has found that lower pH levels lead to lower survival and slower development rates, as well as changes in behavior. Now it’s back to studying Dungeness crab.
“I’m not aware of anyone else looking at potential effects to Dungeness crab,” said Paul McElhany, chief of the Mukilteo station. “It’s interesting, because it’s such a valuable species. It is one of Puget Sound’s top three fisheries. It’s economically very important, and it’s also ecologically very important.”
Two experiments on ocean acidification and Dungeness crab are running at the station.
One experiment looks at the crab’s response to different pH levels throughout the life cycle. Dungeness crab have five life stages: egg, zoea, megalopae, juvenile and adult. Scientists are studying how acidity effects them between each stage.
A system nicknamed the Ocean Time Machine controls CO2, oxygen and temperature to mimic oceans of the past, present and future. The lab has 13 Mobile Ocean Acidification Treatment Systems, each with their own seawater treatment conditions. Each system maintains up to 28 jars. Each jar keeps a crab larva. Computers track pH, oxygen and temperature conditions because all three are linked to the effects of carbon dioxide.
“Oceans aren’t turning acidic. They are acidifying or they are becoming more acidic, but they will never be acidic,” Busch said. “The pH levels are decreasing, and we expect that maybe they’ll get to 7.8 or 7.6, but they’re never going to cross that threshold into the acidic realm.
“An analogy is the North Pole. It is fundamentally a cold place, but we still say it’s warming. But we don’t call it warm.”
A pH less than 7 is acidic and a pH greater than 7 is basic. Right now the mean pH of the ocean is 8.1 on a scale of 0 to 14.
A 0.3 drop in pH may not seem like a lot, but it’s actually huge. That’s because the pH scale is logarithmic: A difference of one pH unit is equivalent to a tenfold difference in hydrogen concentration. A three-tenths decrease in pH is about a 150 percent increase in acidity.
On a recent day, researchers were examining crab metabolism as they morphed from megalopae into juveniles.
“We’re looking at a broader range of response metrics this time, including respiration and molecular changes,” Busch said. “It’s a window into what’s going on with the physiology, meaning how hard is it for you to maintain your body’s functions like breathing and digesting under changing environments?”
It’s a tricky thing to do because it’s essentially an experiment on a gas.
“You need to build the system, have the system working properly, measure the system to make sure it’s working properly, get the animals, keep the animals alive and take the data on them,” she said. “It’s very much a team approach.”
In addition to raising crabs in the MOATS, the scientists also raise them in well plates stored in an incubator. That’s preparation for experiment No. 2.
The second experiment — still very new to the lab — takes a multi-generational look at acidification impacts. Researchers will expose a family of crabs to different pH levels throughout their life cycles. It will take three years to examine one generation.
“We’ll be working on those for a while,” said McElhany, 54, also a research ecologist. “It’s risky to do these long generational studies, but the species is so important that it seemed like a good idea.”
The team recently mated about 50 males and females. It will be a year before the eggs hatch. It will take another two years before the first generation of lab-raised crabs are able to reproduce themselves.
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Sara Bruestle, Herald Net, 8 October 2017. Full article.
