Forbidden Sexual Development Suspected in Unexplained Oyster Die-off
It’s an abnormal sight, really.
Crowded around a makeshift table in the shallows of the Rappahannock River, four Virginia Institute of Marine Science (VIMS) researchers toss around oysters like they’re dealing cards. In waders and life vests, they trudge through calf-high water, bringing up submerged mesh bags, dumping out oysters, and counting them on the table.
Among them is Joey Matt, Virginia Sea Grant graduate research fellow at VIMS. He’s growing these oysters to unravel the mystery of a mass oyster mortality event that happened in the summer of 2014, in which some commercial farms lost up to 85% of their oyster crop.
“We still don’t have an answer to why that happened,” Matt says. “And that’s scary because these farmers—a lot of them¬ can’t afford for this to happen again.”
Matt’s trying to figure out what caused so many oysters to die at once, and he’s got a hunch. Despite being supposedly sterile—meaning they don’t produce eggs or sperm—an unusually high proportion of commercial oysters collected in 2014 were producing sex cells. And Matt thinks this forbidden sexual development may be what led the oysters to their demise.
“Sometimes when an unusual event happens the only way to make sense of it is to connect it to another unusual event,” Matt says.
During the 2014 mortality event, VIMS researchers collected surviving oysters from affected farms. When they popped them open, they expected to see signs of infection indicating that a disease caused the die-off. Instead, they found something much more surprising: some of the oysters were loaded with eggs—as though they were getting ready to spawn.
That’s not how it’s supposed to be. Growers in Virginia prefer to plant sterile oysters; an estimated 91% of oysters planted are sterile, according the 2014 Virginia Shellfish Aquaculture Situation and Outlook Report.
