Acidification of coastal waters
Creatures from mussels to fish affected by more acidic waters
Research in Washington state finds marine life struggling under the double whammy of warming water and increasing acidification of the oceans — both caused by global warming.
FRIDAY HARBOR, Wash. — To understand the bizarre ways changes in ocean chemistry may affect Northwest sea life, there may be no simpler creature to start with than mussels.
When scientists in a Friday Harbor laboratory exposed mussels to slightly acidic marine water, they found the tiny fibres the shellfish use to cling to rocks stayed as strong as ever.
But when the water warmed, those fibres, called byssal threads, became less adhesive — and that could prove deadly.
“Crabs, fish and sea stars love to eat mussels, but it’s hard for predators to pull them off rocks,” said Emily Carrington, a University of Washington professor who has studied mussels for 20 years. “But when waves crash and they’re not firmly attached, mussels get knocked off. Then they fall to the bottom. And that’s crab city.”
It’s the kind of subtle but important change that has become the focus of new marine research trying to grasp how humancaused increases in carbon- dioxide emissions may change Puget Sound and the oceans.
It’s also a sign of a new sophistication in ocean acidification research.
Scientists long have predicted climate change eventually would make waters more corrosive as oceans take up carbon dioxide. The oceans typically measure a slightly alkaline 8.1 on the ph scale that separates an acid from a base.
But in 2007 and 2008, researchers from the National Oceanic and Atmospheric Administration discovered surfacechemistry changes off the West Coast were already happening. In 2010, they found the ph of some Puget Sound waters was an astonishingly low 7.7.
For most of the past few years, those studying how the changes may harm marine life have made astounding discoveries.
As the ph of sea water drops, for example, sea urchin larvae change shape, squid metabolisms slow, some brittle stars and barnacles begin to die, and the shells of oyster larvae start dissolving while they form.
Scientists are now asking more complicated questions as they try to analyze how those changes may alter the way creatures function. They’re no longer looking at simple questions of life or death. Nor are they studying chemistry in isolation, but in combination with other factors — such as shifts in water temperature or changes in wave action in tide pools.
“To do an experiment in a lab to say, ‘ How much CO2 does it take for something to die?’ isn’t the only important question,” Carrington said. “So often, it’s not just acidification that may put animals over the limit, but that in combination with something else.”
That combination can prove significant. Mussels are as important to many rocky sea environments as topsoil is to the agricultural breadbasket of the Midwest: They are a key to the ecological health of nearshore waters. But Northwest commercial growers are already seeing problems with mussel attachment.
Or, take fish. Researchers had long believed that warming seas would drive more fish into colder waters, so commercial fishermen in places such as the North Atlantic could see increases in their catch. But University of British Columbia scientists recently discovered the catch declined when ocean acidification is factored in.
“The field is so young that we’ve really only answered the first stage of questions,” said biologist Michael ( Moose) O’donnell, who works with Carrington. “But the paint is still wet on this picture. We’re still trying to see what it all really means.”
At the Friday Harbor marine lab one recent morning, Emma Timmins- Schiffman, a University of Washington graduate student, plucked a handful of oysters from a tank where she was controlling temperature and water chemistry.
In Willapa Bay, where acidic water regularly wells up from the deep, oyster larvae have been dying for years. Scientists suspect acidification is at least one factor. But is it the driving one?
Oysters, like many creatures in the nearshore, are exposed to a range of temperatures throughout a given day, as the sun rises and sets and as tides move in and out. In fact, organisms living close to shore deal with some of the most variable conditions of any creatures on Earth.
“Some seaweed gets so dry you can crumble it with your hand, then they rehydrate within minutes,” O’donnell said. “Then they’re back up and humming as if nothing happened.”
So Timmins- Schiffman not only is exposing these shellfish to lower- ph water. She’s also changing water temperature and triggering the oysters’ stress response. In some cases, she’s checking for changes in respiration and feeding efficiency. Her results are expected this year.
Meanwhile, at a related lab in Seattle, researchers with the Northwest Fisheries Science Center lab in Montlake are trying to look at effects across the food web. Because the marine food chain is complex and confounding, they’ve determined that, while some species may crash as acidification takes a toll, others may thrive. For example, when one type of plankton declines, so do the herring that eat it. But when populations of a different herring food collapse, the herring population increases.
“There can be this dampening effect as impacts on predators and prey counterbalance each other,” said Paul Mcelhany, of the Montlake lab. “In some cases, it’s more than you would have expected. In a lot of cases it’s less.”
Until recently, researchers presumed that fish — unlike shellfish and some important plankton species — largely would escape direct effects from carbon- dioxide emissions.
But an Australian scientist working with clown fish found the exposure to more acidic water affected their ability to flee predators. So Mcelhany’s lab has been looking at the effects of ph changes on China rockfish and surf smelt — important Northwest species. Results are expected this spring or summer.