For months, they tried to perfect the treats — molding, mixing, baking, again and again.
Taste-testing wasn’t a good idea — their dough was made with ground-up seashells. But the four Northwestern students who worked on them for a class project, with help from the Shedd Aquarium, hope certain sea creatures will find them irresistible.
The treats, dubbed GastroPops, have a hard outer casing and a soft seafood filling — kind of like cream puffs for sea creatures, said Hannah Levin, a Northwestern senior. They’ll be used to study predators in marine environments.
That outer casing is shaped like the shell of a marine snail, also known as a conch. The seafood filling, which is water soluble, serves as the bait, drawing in predators by releasing a strong odor.
GastroPops is a play on the word “gastropod,” which means snail — except in this case, “the snail stays in place and doesn’t move away,” said Andy Kough, a Shedd research biologist.
Scientists will use GastroPops to measure how often those predators, including lobsters and stingrays, eat shelled creatures, like clams and shrimps. This information helps scientists measure ecosystem health and the effects of conservation efforts.
Some conch species are listed as threatened, so the aquarium wanted to find a way to measure how often conches are preyed upon — without putting real ones in harm’s way, according to Kough.
“Instead, we came up with an artificial method to replicate that experience, so we can do it many, many different times and in many, many different places,” Kough said. “That would be our GastroPop.”
Predators who try to eat the GastroPops will leave evidence, Levin said..
“Once we put [the bait] in water, it swells up and can’t come back out unless the shell is broken or manipulated by an animal,” Levin said.
The team also had to make sure GastroPops wouldn’t harm the ocean, because “we didn’t know if any pieces were going to get left behind, or ingested by animals.”
The four students started working on the GastroPops last fall, finding inspiration in the restaurant where one of them worked.
That restaurant’s Happy Hour deal for oysters meant lots of leftover shells. The student brought some to the team, and they learned they could pound them into a powder.
“We boiled them. We smashed them with hammers,” sifting the result to get the powder, Levin said — until they found out they also could just order the powder in bulk. Turns out, oyster shell powder is often used in construction work, as a filler for concrete.
The students mixed the powdered oyster shells with sodium alginate — an adhesive binder also used to make boba pearls.
They molded that cement-like result into the shape of a shell.
“We started calling it ‘conch-crete,’” Levin said.
“We tested a bunch of different temperatures to bake it at,” she added. “We did it at someone’s apartment. It did not smell good.”
After plenty of “trial and error,” the team had their GastroPop. Then, they visited the aquarium to see how species responded to it — and the Caribbean Spiny Lobster “absolutely loved” it, Kough said.
“She was a little hesitant at first, smelling it,” Kough said. “Then she walked over, grabbed it and took it to her den, where she proceeded to shred the shell to eat the tasty treat within.”
Scientists have struggled to measure how often predators eat shelled creatures, because they don’t have the tools, Kough said.
But the team hopes GastroPops can change that. Later this month, the students will travel to Miami to try out them out in the field, setting up 60 shells at different sites around the Caribbean.
Animals respond to GastroPops differently. A spiny lobster will chip and peel it, while a stingray will crush it with its jaws, Levin said.
“A pattern of cracks around the spire could show that it’s probably a spiny lobster, as opposed to a sea turtle,” Levin said. “Different types of interactions also give clues as to which predators are in the area even if it wasn’t caught on camera.”
By studying the results, Kough said, the project could “provide a tool to future scientific studies that are looking to see ‘who’s eating who.’”