by A mass die-off of oysters is occurring along the U.S. coast, leaving farmers desperate and scientists struggling to find answers to the cause.
For more than a decade on the East Coast and Gulf of Mexico, millions of farmed oysters grown in cages or bags in tidal areas have fallen victim to Sudden Unusual Mortality Syndrome (SUMS), which causes the flesh in the shell to be destroyed tear down.
It was devastating to the seasonal oyster industry, causing some farms to close completely and others to relocate further north. And scientists believe they are just beginning to understand the scale of the problem.
“I have grown adults almost in tears when they call about this. Because it’s a punch in the gut that you don’t know what to do to make it right,” said Bill Walton, a professor at the Virginia Institute of Marine Science The Independent this week.
He added that oyster losses were a “significant problem” in the Southeast and Northeast this year. “I promise you, it’s not the producers’ fault,” he said. SUMS has been reported as far south as Texas and as far north as Maine.
In the Chesapeake Bay region of Virginia, where more than 50 million oysters are farmed, sudden mortality syndrome has been on the rise for a decade, Walton said.
In January 2021, millions of pounds of oysters were found dead along the banks of Louisiana’s Plaquemines Parish, with some farmers suffering a total loss.
“So we respond to the burning houses [and] try to help them. “But, ‘Why don’t other houses catch fire?’ is an important question that will help us figure out the ‘why,’” Walton said.
Professor Ryan Carnegie, who works with Walton in the Shellfish Aquaculture Program, said the disease had been devastating for many of the farmers he spoke to.
Carnegie examines thin slices of oyster tissue on microscope slides, which help him detect stress and disease. But if you look under the shell, many oysters seem to be doing well. “They’re dying from something, and it’s not parasitic diseases,” he said.
A recent report by marine experts at eight schools, including the Virginia Institute, found that mortality rates at oyster farms on both coasts exceed 70 percent year after year.
Although these die-offs generally occur during peak reproductive seasons, early spring and summer, oysters can also be affected at other times, and environmental conditions could be a factor.
“We know that our marine environment becomes even more stressful under the stressful conditions of intensive aquaculture… Peak temperatures can be very high. We are struggling with low oxygen levels,” Carnegie said.
The North Atlantic has seen record sea surface temperatures over the past 18 months, with the heat wave putting great strain on ecosystems. The same was true this year in the Gulf of Mexico.
Genetics could also play a role. Some oysters are bred sterile so they can grow faster, meaning they carry an extra set of chromosomes. Carnegie wondered whether this genetic burden could weaken their chances of survival when water temperatures are high and food sources are scarce.
“So is this burden just too great in a challenging time of year to drive these Thoroughbreds, who are really built for market size, into the ground?” he asked.
Walton said scientists still can’t really get a handle on the scale of the problem because they only respond to oyster farmers’ individual problems. The scientists now plan to work with 20 commercial farms from Virginia to Texas to test oysters while monitoring environmental variables such as ocean temperature and salinity.
For now, the best they can offer is help testing oysters under stressful conditions. But that is not a solution.
“There are farms that have moved their entire property for this reason, and it’s not easy and it’s not cheap,” Walton said. “So on an individual level it’s a question you have to ask whether it makes sense to continue with this.”
