The research behind restoring scallops to NC waters

Researchers tether baby scallops in an experiment to understand how best to restore them.

Amy Yarnall popped out of the shallow waters of Oscar Shoal, pulled the snorkel out of her and pushed her dive mask onto the top of her head. Clearly excited, she then held the mollusk up in the air, as if it was a trophy.

“I found a live adult wild bay scallop,” exclaimed Yarnall, a Ph.D. candidate at the University of North Carolina Institute of Marine Sciences. “They get to be a bit larger than this, so I would call this a teenager or juvenile.”

But it’s sad to say, this is a pretty lonely teenage bay scallop. To find out why, drive down to the sandy sea grass beds at the bottom of North Carolina’s bays and estuaries. Swim over the sea grass meadows.

The little creatures have a neat life history. Bay scallops float through the water as a larvae, inside a little shell that looks just like an adult. It’s not clear how the tiny bay scallops know this, but they find clues that indicate sea grass in the area. They float down, or swim down, and using bissel threads they attach to the sea grass. Bissel threads are tiny lines that emerge from the shell. The scallops grow while tied to the grass, until they are big enough to drop to the bottom and they live laying on the bottom.

Those sea grass beds were filled with bay scallops in the 1920’s. North Carolina topped the nation with 1.4 million pounds harvested. But a red tide in the 1980’s decimated the population. Overfishing, natural predation, and a decline in sea grass caused by rising water temperatures and lower water quality all combined to put the species at risk. The bay scallop population never recovered and the fishery was closed in 2006. It hasn’t been reopened.

So, the scallop Yarnall found is a pretty lonely teenage bay scallop. It’s also appears to be mad, opening and closing its shell about every 30 seconds.

“They can flap their shells together in order to propel themselves through the water and that’s how they swim,” says Yarnall, putting the scallop back in the water. “It’s upset and I don’t want it to dry out so it’s time to say goodbye.”

But now the bay scallop is getting some love thanks to a research project Yarnall is leading. “All species are important to the biodiversity of our ecosystem and while it sounds bad, the most important function bay scallops serve is as prey for other species,“ Yarnall adds, watching that teenage scallop swim away. “But they also perform a filtering function similar to oysters, and estuaries are becoming more filled with nutrients, sediments, and these guys are one of the critters that can filter out things that are detrimental to our ecosystem.”

The unique research project requires a lot of patience, along with a drop of glue, fishing line, metal frame and living juvenile bay scallops. Scientists are tethering more than 1600 living juvenile bay scallops to marked steel frames and planting them underwater. “This project is to discern why bay scallops have not recovered, and what would be the best way, artificial grass beds or natural grass beds, to focus our restoration efforts,” says Yarnall.

The living scallops are tethered because they can swim through the water. The frames and tiny tethered scallops are then placed in nine artificial sea grass beds on Oscar shoal, just off Beaufort. The beds vary in size and thickness. Bay scallops were once abundant in the area Researchers will return to the tethered scallops day after day to follow the fate of the scallop through time.

The surveys will reveal not only if the scallop is still alive, but after a week the growth rate can be checked. Survival and growth are important for restoration. Researchers expect to find survival and growth rates will differ between seagrass landscapes. Once researchers determine which bed has the best survival rate, more than ten thousand scallops will be scattered throughout the natural and artificial sea grass beds to see where they prefer to locate themselves without human intervention. Those scallops will also be monitored to see how well they survive and grow.

“We can build big continuous sea grasses or small patchy sea grasses but first we need to see what works best,” said Joel Fodrie, Ph.D., associate professor of Marine Sciences at the UNC-IMS. “The scallop is a great model for understanding how these systems work because it’s a nice fairly sedentary species that we can tag and tether to determine the fate of the individuals we put in the landscape."

Fodrie said the bay scallop is also valuable because it is part of North Carolina’s history. “It’s a species that we want to know what makes it tick so we could tweak the system if possible in a way that could help scallops” said Fodrie. “It’s also possible that if we understand the system, we could plant baby scallops in the best system for their survival to try and restore them.”