NOAA research links human-caused CO2 emissions to dissolving sea snail shells off U.S. West Coast

November 22, 2016 – For the first time, NOAA and partner scientists have connected the concentration of human-caused carbon dioxide in waters off the U.S. Pacific coast to the dissolving of shells of microscopic marine sea snails called pteropods.

Commercially valuable fish such as salmon, sablefish and rock sole make the pteropod a major part of their diet.

“This is the first time we’ve been able to tease out the percentage of human-caused carbon dioxide from natural carbon dioxide along a large portion of the West Coast and link it directly to pteropod shell dissolution,” said Richard Feely, a NOAA senior scientist who led the research appearing in Estuarine, Coastal and Shelf Science. “Our research shows that humans are increasing the acidification of U.S. West Coast coastal waters, making it more difficult for marine species to build strong shells.”

The global ocean has soaked up one-third of human-caused CO2 emissions since the start of the Industrial Era. While this reduces the amount of this greenhouse gas in the atmosphere, it comes at a cost to the ocean. CO2 absorbed by seawater increases its acidity, reducing carbonate ions, which are building blocks used by shellfish to grow their shells.

 (NOAA)

The pteropod, a sea snail the size of the head of a pin, is found in the Pacific Ocean. It has been the focus of research in recent years because its shell is affected by how much CO2 is in seawater and it may be an indicator of ocean acidification affecting the larger marine ecosystem.

A key piece of the new research was determining how much human CO2  emissions have added to naturally occurring CO2 in seawater off the U.S. West Coast. Using several decades of measurements from the Pacific Ocean taken through the U.S. Global Ocean Carbon and Repeat Hydrography Programoffsite link and new data from four NOAA West Coast research cruises conducted between 2007 and 2013, the research team developed a method to estimate additional CO2 from human-caused emissions since the start of the Industrial Era as compared to CO2 from natural sources.

The analysis shows that concentrations of human-caused CO2 are greatest in shallow waters where the atmosphere gives up large amounts of its CO2 to the sea. The researchers also estimated that CO2 concentrations from fossil fuel emissions make up as much as 60 percent of the CO2 that enriches most West Coast nearshore surface waters. But the concentrations dropped as they measured deeper. It drops to 21 percent in deeper waters of 328 feet or 100 meters, and falls even lower to about 18 percent in waters below 656 feet or 200 meters. Concentrations vary depending on location and seasons as well.

Once researchers created a detailed map of the human-generated CO2 concentrations, they  looked at how pteropod shells fared in areas with varying seawater CO2 concentrations. They found more than 50 percent of pteropod shells collected from coastal waters with the high CO2 concentrations were severely dissolved. An estimated 10 to 35 percent of pteropods taken from offshore waters showed shell damage when examined under a scanning electron microscope.

“We estimate that since pre-industrial times, pteropod shell dissolution has increased 20 to 25 percent on average in waters along the U.S. West Coast,” said Nina Bednaršek of the University of Washington. Earlier research by Bednaršek and others has shown that shell dissolution affects pteropod swimming ability and may hamper their ability to protect themselves from predators.

“This new research suggests we need a better understanding of how changes in pteropods may be affecting other species in the food chain, especially commercially valuable species such as salmon, sablefish, and rock sole that feed on pteropods,” Bednaršek added.

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Sea Snails on Acid

Twice a day the rocky Pacific coast traps seawater in pools as the tide rolls in and out. Compared to the ocean, the puddles are so small and innocuous that it seems nothing momentous could possibly be happening there, but there is. It turns out tiny black turban snails may be getting a buzz from the changing levels of acidity caused by ocean acidification. The scientists at Bodega Marine Lab looked closely at sea stars and snails to find out.

The underside of the purple sea star is covered in tiny delicate suction cups that make one wonder how it moves fast enough to be a voracious hunter, but it is. It’s the bully on the playground, a merciless predator. It can pry open mussel shells, turn its stomach inside out and wrap it around large prey, and digest its meal before even swallowing. It’s no wonder that when black turban snails sense the purple star’s arrival, they all flee to safety, crawling quickly up the side of a tide pool until the enemy leaves the water. Quickly for snails, that is.

Snails have always been good at running away from their primary predator – the purple sea star – until now. Brittany Jellison, a graduate student at University of California Davis, has found in a recent study that the snail’s dramatic response might be slowing down because of ocean acidification. Jellison modified tide pools to mimic ocean acidification conditions. Then she observed the snail’s response by measuring the path they took to safety. What she found when watching the snail was a trippy set of behaviors.

“Elevated carbon dioxide is a foreign substance in seawater, and snails are taking that foreign substance into their body, so yes, they in essence are on drugs,” said Brian Gaylord, a professor at UC Davis Bodega Marine Lab, where Jellison discovered that under ocean acidification conditions, snails didn’t immediately flee the pool to safety.

Ocean acidification occurs when the ocean absorbs excess carbon dioxide from the atmosphere.  While most scientists studying the phenomenon are trying to understand how it effects a single species in a lab, Jellison’s work explores how ocean acidification effects multiple species interactions.

“I think what’s really important here is that she is moving beyond thinking about an individual species, and instead thinking about how the direct effects on individuals scale up when they are in nature and interacting with other species. That is the important part of it,” said Kristy Kroeker, Assistant Professor at the Department of Ecology and Evolutionary Biology at University of California Santa Cruz.

Professor Philip Munday of James Cook University agrees. He studies how ocean acidification effects reef fish and their ability to adapt to a changing environment.

“Ecosystems are a whole combination of interactive species,” said Munday. “If we want to understand how ocean acidification is going to impact marine ecosystems we need to understand how it will impact with the really critical ecological interactions, such as predatory-prey interactions. That’s one of the really exciting things about Jellison’s work.”

Tide pools on the Pacific coast have natural fluctuations in acidity, and the black turban snail and other animals that live there have adapted to that. Jellison wondered if the snails would be tolerant to ocean acidification conditions as well, or if they would reach their tipping point, and no longer able to tolerate the changes.

To find out, Jellison made model tide pools in aquariums. So that the snails would feel most at home, she simulated the conditions of natural tide pools, with one exception. Jellison changed the levels of acidification in some of the pools to mimic the levels that are expected for rock pools under ocean acidification by the year 2100. Having some tide pools with normal conditions and some with future acidic conditions allowed her to compare the behavior of sober snails with snails on acid.

With the arena built, let the show begin. Clutching her camera, Jellison carefully lowered black turban snails into the tank. One by one the snails reacted to a chemical cue produced by the predator sea star. Jellison took photos every two minutes for a half hour, then analyzed them for the distance the snails traveled, where they moved, and most importantly, if they left the water and escaped to safety. In total, Jellison did two 5-day trials, created 32 aquariums, tested 32 snails, and took photos every two minutes for 28 minutes per snail.

Under normal conditions, the snails will run away and exit the water, a flight response that keeps them safe. Jellison found that in water with higher acidity the snails started to run away, but instead of moving to dry ground, they seemed to get confused, haphazardly meandering around the pool.

Ocean acidification’s ability to change the interactions between predators and prey can have far reaching consequences. Jellison and her team aren’t yet sure exactly why the snails act confused. They think it’s related to changes in the brain as the animal tries to maintain balanced brain chemistry, which is something they would like to understand further.

“I really love research and I especially love working with marine animals,” said Jellison, “but when I think about what my work is saying about the future it can be a little bit hard to take in. Most of the things we are finding is that the world is going to look very different form what we see today.”

In the meantime, Jellison continues this research out in the field, in a creative study that has her waking up at all hours to hike to the tide pools and observe snails – all to understand the cascading effects of ocean acidification on the ecosystem. “I have a lot of hope that we will move forward as a society and try to come up with solutions and actually make changes. It is having hope that is important,” said Jellison.

Ocean acidification may cross national boundaries, and reach all corners of the earth, but a glimpse into a puddle of seawater reveals an elaborate community, a tiny snail, and a big message.

Read the original post: https://blogs.scientificamerican.com/guest-blog/sea-snails-on-acid/