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Swimming pattern of tiny marine mollusk holds promise for researchers

The climate change debate has many looking skyward to gage the effects of greenhouse gases, but an interdisciplinary team of scientists from Georgia Tech and Johns Hopkins University is taking another view: the ocean.

Supported by $720,000 National Science Foundation (NSF) grant, the team will be learning more about ocean acidification (OA) by studying the swimming patterns of a tiny but plentiful marine mollusk, the pteropod (“tarro-pod”).

“It’s similar to the way we’ll send a canary into a coal mine to check the air,” says Professor Jeannette Yen, who heads up Georgia Tech’s Center for Biologically Inspired Design. “We can find out a lot about how sick the ocean is by studying how these organisms move.”

The three-year study will take Yen and CEE’s Dr. Don Webster past the tip of Patagonia to Antarctica where they will collect specimens of the creatures, study their swimming behavior, morphology, and induced-flow patterns to gain a fuller understanding of the actual and projected effects of OA.

The team will also travel to Svalbard (in 2015) off the northern part of Norway to study pteropods at high northern latitudes. The results of their field and lab experiments will be shared with Johns Hopkins’ Dr. Rajat Mittal, who will employ computational fluid dynamics (CFD) modeling to better predict the effects that different conditions will have upon the pteropods propulsion and, ultimately, their survival.

The group chose pteropods because they perform many functions in marine ecosysteDr. Don Websterms and because they are sensitive to changes in the ocean’s pH. Their outer shells are formed from aragonite, a material which is easily degraded by the lowered pH levels of water that has absorbed excess atmospheric CO2.

The researchers predict that, as their shells become thinner, the pteropods’ method of locomotion will change to account for their increased buoyancy and altered center of gravity.

“So, in the future, if we see them behaving differently, we can see it as an early warning, as evidence that the pH is changing in the ocean,” said Webster.

Webster and Yen both pointed out that the pteropod is a primary food source for the upper trophic levels of the ocean, making fluctuations in its survival rates a primary concern for other animals in the food web as well as the fishing industry. Pteropods are also responsible for more than 50 percent of the ocean’s carbonate flux, another important component of the ecosystem.

“But at this point, we need to know more about how pteropods move and how they behave in different conditions,” says Webster.

Biomechanically speaking, pteropods are truly “odd ducks.” They move through the ocean using a “clap and fling” motion that is more like flying than swimming. With each upward propulsion of their wing-like parapodia, their trajectory through the water is wobbly and jagged, but well-adapted to their survival. Further, they resist backward motion by spinning a light mucous web.

“We know that ocean acidification will likely affect their motion because it causes their shells to thin,” said Webster. “Will that make them wobble more? Will they rise higher and sink more slowly because they weigh less? Will increased motion make them more noticeable to predators?”

The answers to those questions will come from extensive field work and computer modeling that will begin in the spring of 2014, when Yen, Webster, and a team of students will travel to Palmer Station, Antarctica to begin collecting and observing (southern) high latitude pteropods.

Webster and Yen will employ high-resolution videography and 3D tomographic Particle image velocimetry (PIV) combined with fluid dynamic modeling to better understand how the pteropods’ wings propel themselves. The team will also evaluate the efficiency of their propulsion and identify the factors that influence their swimming trajectory.

Yen anticipates some significant findings but she hesitates predicting. Right now, it’s all about the questions.

“If their lighter shells make them better able to propel upwards, will they swim through a primary source of food and find themselves facing new predators? We don’t know.”

What she and Webster do know is that the multidisciplinary focus of this project will provide a wealth of data that will advance several areas of research, from biomechanics to ecology to modeling.

“When we study the way pteropods move, we think it will inspire a new designs for underwater vehicles,” she said. “There are a lot of possibilities in this research.”

cross section of pteropods