Oyster habitats are rapidly disappearing around the world. That doesn’t just mean losing a delicacy. Oysters also play a major role in coastal environments. A team of scientists on Mobile Bay is working to turn that loss around. That effort may have national impact.
Bayou La Batre has been a fishing port on Mobile Bay since the 18th century. On a recent morning, scientists, graduate students set out from the port to put seafood back into the bay. They filled hundreds of mesh bags with shells that will become a home for millions of oysters. They’re hoping that this could be one way to reverse a trend in which the world oyster population has been cut by 85 percent.
“It's the most degraded habitat in the world,” said Lee Smee, senior marine scientist at the Dauphin Island Sea Lab.
“Most of that is due to overharvesting, but when you then couple that with either too dry and too salty in some parts of the Gulf or too wet and too fresh in Alabama and Mississippi, predators, continued harvesting. They face a lot of challenges,” he said.
One way that sea lab scientists are helping oysters face those challenges is to give them a better start to life. Baby oysters, in this case 12 million to 20 million, are grown in the lab until they’re about one month old. When they start growing their own shells, they’re known as spats. At that stage, Smee says they’ll be put out on the reef.
“And, the reason we started doing that, the population of oysters have gotten so low. There's just not enough naturally occurring spawning going on and so, when you just put shells out, that's no longer enough to just rebuild a reef and so we're doing the spat on shell to compensate for that,” Smee said.
But the real key to survival might be a form of tough love. The babies are deliberately frightened by a spat’s worst nightmare. Lee Smee explains how these scare tactics work
“The experimental side of that is part of that spat on shell gets exposed to a predator cue, in this case a blue crab that's caged that we've been feeding oysters to,” he observed. “That makes some of the oysters toughen up their shells because oysters are known to toughen up, harden their shells when predators are around and then we're experimentally building the reef so half the reef's built with toughened up oysters and half of them are controls that didn't get the predator cue.”
The fear factor seems to work. Oysters in the first reef were three times more likely to survive if they’d been exposed to predators.
“Last year, we found that mortality in the ones that were not exposed to predators, after about six months, was 90%, which isn't terribly unexpected for oysters. They spawn a lot and a lot of them die, but that rate was like 70 % in the ones that had predator cues. So, we saw a really easy big way to make the process more effective,” said Smee.
Making the process more effective means finding a process that works on a large scale for oyster farmers, not just in a lab.
“Our goal was to find some way to toughen them up,” said Ben Belgrade, a research scientist at the Dauphin Island Sea Lab.
“We started working on Auburn University Shellfish Laboratory to see if we could toughen oysters at a commercial-industrial scale where before we were doing this in little containers, toughening up maybe a couple of hundred oysters at a time. That's not going to work for reef restoration. We need to be able to do this to millions of individuals simultaneously,” he insisted.
One key is what exactly makes scared oysters grow thicker shells.
“Our next goal with this is to actually be able to identify the molecules that the predators are releasing and be able to just synthesize those in the lab and fertilize our oysters with them like we fertilize our crops with nitrogen to make them grow bigger, we want to fertilize our oysters with predator cues so that they grow tougher,” said Belgrade.
Belgrade says this research isn’t just useful in Mobile Bay or on the Gulf.
“This technique can be used nationwide,” he insists. “It's not just us that can use it. This is a technique that would probably be able to be used in California West-Coast oysters. This is a technique that can be used in the New England region.”
Matthew Ogburn is a research ecologist with the Smithsonian Environmental Research Center. He says projects like the one in Mobile Bay could help reverse the decline of oyster populations. Ogburn says projects like the work on Mobile Bay could be one way to reverse that trend and increase oyster populations.
“The idea of testing whether oysters will do better if they're exposed to predators or the water that predators have been in, the scent of predators before those oysters are planted out on the reef is a really interesting one that potentially has a lot of value,” he said.
“Oysters are really important, not just as food, but as a cultural resource for this part of the coast,” said researcher Christa Russell with the Dauphin Island Sea Lab. She says producing oysters isn’t just about preparing something to be served on the half shell.
“But, yes, they're incredibly important for this part of the ecosystem. These guys can filter a tremendous amount of water,” said Russell. “They're what's called an ecosystem engineer. So, they change their ecosystem by building these reef structures, by building these shells that they create habitat from nothing.”
Russell is already seeing results from the first experimental reef set out last year.
“Lots and lots of organisms use that habitat, everything from tiny little invertebrates and worms, which don't seem important, but fish need food too, to little baby fish that you'll find,” she said. “I've seen oyster skimmers out here feeding on my reef. I've seen larger fish. I saw some dolphins come in and feed on schools of fish hanging out by the reefs. So, they're really, really important for maintaining this complex ecosystem just because they build a structure that wouldn't be here otherwise and they're food for lots of things other than people too.”
The project is also inspiring a new generation. On shore, Mobile Boy Scouts worked to fill bags with shells. Fifteen year old Ethan Gates helped direct the effort as part of his Eagle Scout project.
“I was looking for my project,” said Gates. “I wanted to do something like this, make an artificial reef and he told me about it and I thought it was an open opportunity. I thought it was something I'd like to do. I think it's a good project. Hopefully, it'll bring back some of the oyster life around here. We like oysters around here. They have more than we can just eat them. They help filter out the water. They can make whole new waterways. They can change the way the water goes, change erosion. They've been restoring the shoreline and the locals seem to like it.
Scientists and others have a long way to go to restore the oyster population, but Lee Smee at the Dauphin Island Sea Lab says that things are off to a good start.
“I am pleased and baring a hurricane or some other catastrophic thing like that, the reef is doing well and it's healthy,” said Smee.
