UW makes waves in ocean acidification

Photo credit: E. Carrington

Photo credit: E. Carrington

The San Juan archipelago, perhaps most famous for its pod of southern resident killer whales, is also home to the UW’s world-renowned biological field station, the Friday Harbor Laboratory (FHL).

Built in 1910 on the former Point Caution military reserve, FHL has grown from a single building to a sprawling campus with over a dozen specialized laboratories.

A waterfront trail, which meanders past the stand-alone research buildings, serves as a timeline of the facility’s growth. The farther along the trail you go, the newer the labs become. Eventually, the trail dead ends at the newest addition: the Ocean Acidification Environmental Laboratory (OAEL).

Interest in ocean acidification at the UW began with professor of oceanography Richard Feely. Through his work with the National Oceanic Atmospheric Administration’s (NOAA) Carbon Program, Feely highlighted worrisome trends in ocean chemistry and inspired scores of scientists to take a closer look.

“Ocean acidification was really off the radar for everyone 20 years ago,” said Emily Carrington, a professor of biology at the UW and the OAEL’s first director. “Largely because of [Feely’s] efforts and many others, the University of Washington and Washington State [University] are at the forefront of ocean acidification research, regionally and globally.”

Before the OAEL was built in 2011, a postdoctoral fellow named Moose O’Donnell built the first experimental acidification system with Terrie Klinger, the director of UW’s School of Marine and Environmental Affairs. Though the setup was limited in its experimental capacity, researchers all across campus realized its potential and quickly moved to expand upon their work.

“Everything just started to fall into place,” Carrington said.

Among a small forest of spent CO2 tanks, lab manager Becca Guenther directs the end-of-summer rush as researchers collect their final data points. Between the 90 degree weather and constant heat of the lab’s machinery, it’s hard for anyone to forget about climate change.

The only relief from the heat comes from cold seawater running through the lab’s experimental chambers called mesocosms. These customized tanks are essentially large coolers where researchers can manipulate parameters such as pH and salinity to observe how organisms respond.

“The beauty of the mesocosms is that we can precisely control the conditions, but that’s also their limitation,” Carrington said. “We’re essentially doing experiments in a tiny bucket and it isn’t the ocean. The ocean is much bigger and more dynamic, so we have to be careful about the context in which we’re doing our experiments.”

According to studies by Christopher Sabine, a UW professor of oceanography and director of NOAA’s Pacific Marine Environmental Laboratory, the ocean absorbs around half of all man-made CO2. The ocean’s ability to sequester carbon dioxide has dramatically slowed the rate of atmospheric warming, but at a price.

CO2 dissolves in seawater to form an acid. The ocean absorbs an estimated 2.5 billion tons of CO2 every year. When those dissolved gases react with seawater, they produce highly reactive hydrogen ions, or protons, which accumulate and drive the pH down.

“We are incredibly lucky the ocean absorbs as much CO2 as it does,” FHL director Billie Swalla said. “The fact that we already have so much CO2 stored in the ocean is scary, and it looks like it’s only going to get worse. It’s very hard to change people’s behavior.”

According to a 2014 report by the Intergovernmental Panel on Climate Change (IPCC), the ocean is already 0.1 unit more acidic than pre-industrial values, with models predicting average pH to be 0.3 – 0.4 units more acidic by the end of the century.

These changes may sound insignificant, but they represent an unprecedented shift in ocean chemistry. A 0.1 drop in pH means the ocean is 30% more acidic than it was in 1800.

If the IPCC models are accurate, the oceans of 2100 will be more than twice as acidic as they are today.

“There’s anthropogenic ocean acidification from us putting CO2 into the atmosphere and burning fossil fuels, but there’s also these natural processes that affect pH,” Guether said. “It’s kind of both at once, so teasing apart how much of this is from us versus natural variability can be hard to do.”

The Salish Sea is naturally more acidic than the open ocean. The same factors that make it relatively acidic, such as freshwater input from rivers, contribute to its high levels of variability.

One important natural input of low pH water comes from a process called upwelling. When the strong currents collide with the Washington coast, they force cold, nutrient-dense water to the surface. The deep ocean acts as a reservoir for dissolved CO2, which takes years to reach the surface again.

“There’s a delay time,” Guenther said. “So even if we stopped using all fossil fuels today, we would still be seeing the effects of what we did the last 50 years for the next 50 years.”

Due to high levels of variability, most researchers refer to the trend in acidification as a shifting baseline. The fluctuations in pH remain the same, but the extremes get progressively more acidic.

As that baseline gets lower and lower, the frequency, duration, and severity of these low pH events all increase.

Disappearing skeletons

The Washington Ocean Acidification Center (WOAC), created in 2013 to bolster research efforts statewide, sends Guenther a near constant stream of water samples from the Salish Sea and Pacific Ocean to be analyzed at the OAEL’s analytical chemistry lab. This gives researchers a better idea of what conditions organisms face in the ocean.

This approach reveals current conditions, but to understand what the ocean was like millions of years ago, scientists turn to fossils.

While working on her doctoral dissertation at Princeton University, Anne Gothmann studied fossilized coral skeletons. By analyzing the chemical makeup of the skeletons, she could infer the conditions in which they lived.

“[Corals] make their skeletons from the metals and ions in the seawater, so a lot of what the ocean chemistry looks like is actually recorded in coral skeletons as they build them,” Gothmann said.

Now a postdoctoral fellow in UW chemical oceanographer Alex Gagnon’s lab, Gothmann has turned her attention to living corals. Balanophyllia elegans, or the orange cup coral, lives in the cold water of the Salish Sea. Unlike tropical corals, these live in the deep ocean where pH is relatively low.

Corals, like many marine invertebrates, make their skeletons out of a molecule called calcium carbonate. In order to grow, or calcify, an organism must combine one calcium ion and one carbonate ion. Calcium is widely abundant in the ocean, but carbonate ions are not, which limits an organism’s ability to grow.

Low pH conditions challenge calcifying organisms from two angles. The hydrogen ions in relatively acidic water dissolve an organism’s existing calcium carbonate skeleton and also react with free carbonate ions in the water, making them unavailable for growth.

Organisms must build as much skeleton as they lose just to maintain their size and strength. As pH drops, calcium carbonate dissolves progressively faster and becomes harder to replace.

This begs the question: does living in a naturally low pH environment make organisms better adapted to a shifting baseline or are they even more vulnerable to falling below some fatal threshold?

“That’s the million-dollar question right there,” Carrington said.

Cracks in the foundation

Similar to the fundamental role coral reefs play in the tropics, shellfish in the Salish Sea support a vast network of species up and down the food chain.

Mussels and oysters are foundational species, meaning they play a huge role in regulating the flow of nutrients through the ecosystem and providing habitat for many other species.

“To a certain extent, every species matters in an ecosystem, but some do matter a bit more because they have stronger effects on other species that they interact with,” Carrington said.

Like coral, bay mussels build their shell out of calcium carbonate. By exposing groups of adult mussels to different pH treatments, Carrington quantified the effect increased acidity has on biomaterials. This involves measuring the physical makeup of an organism’s body parts, such as how strong, sticky, or stretchy it is.

As expected, mussels exposed to low pH seawater for five weeks had consistently weaker shells than those in high pH treatments. The results also showed that byssal threads, protein fibers that mussels use to cement themselves to the substrate, don’t stick as well in relatively acidic water.

“So that was a bit of a surprise because it’s a non-calcified material,” Carrington said.

This change in byssal threads makes mussels more vulnerable to being dislodged by strong waves or predators. Mussels and oysters get their nutrients by filtering seawater, so they must be cemented to some solid object in order to properly feed. If low pH conditions prevent them from adhering to the substrate, they will starve to death.

“Often, organisms are living very near their limits,” Carrington said. “By pushing them a little bit farther to their physiological limits, it’s often a very steep drop in performance. That’s the concern: A little shift in the baseline is going to cause catastrophic problems.”

Due to their foundational role in the Salish Sea, a decline in mussel and oyster populations due to ocean acidification could spell disaster, and changing ocean chemistry is just one of many threats marine organisms face, a fact not lost on FHL director Billie Swalla.

“We’re in the middle of a mass extinction event right now, unfortunately,” Swalla said. “The question is: How far will it go?”

Timothy Kenney, UW The Daily, 26 September 2016. Article.


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