Stony Brook student tests scallop die-off theories

With the local population of Peconic Estuary Bay Scallops apparently impacted by what appears to be another massive summer die-off, marine biologists across the region are scrambling to figure out why and test their various theories with rigorous scientific principles. before resigning to a singular cause.

While some scientists are working on a selective breeding program that hopes to exploit what may be genetic inclinations in the few scallops that have survived the devastation of previous years, others are testing theories about the extent to which predators can play a role in death. -off not understood before.

A young Stony Brook University graduate student definitely hopes to show whether a voracious ray species that arrived in local waters the same year scallops suffered the first summer kill might play a bigger role in the scallops’ demise. than previously believed. .

Jessica MacGregor joined the lab of Professor Brad Peterson Ph.D. at the Stony Brook School of Marine and Atmospheric Sciences in 2019, just after the discovery of the first scallop kill in the bays and just when the abundance of cownose rays that were invading the bay which year was considered a possible culprit.

Conventional wisdom was that cownose rays — which can weigh up to 50 pounds each and swim in shoals of several dozen — were probably not a major player in the scallop die-offs of previous years, largely because ‘They don’t tend to appear in local waters until August and the bulk of deaths are thought to occur in mid-July. Additionally, scientists said in the first year of mass kills that they saw the shells of dead scallops resting on the bottom of the bay where they died, rather than being pulverized by the jaws of the rays.

But Peterson said the number of “cluckers,” as the researchers call the shells of dead scallops, observed following the fatalities isn’t enough to rule out that predators aren’t to blame for at least a significant portion of the deaths. scallop deaths.

“We worked with Steve [Tettelbach] and [Cornell Marine Program] to answer two questions: whether subsequent spawning that might occur at a time when the physiological compromise of warm water for animals after spawning might be enough to push them overboard,” Peterson said, “or whether we have a new predatory potential that causes high losses.

To put competing theories to the test, MacGregor devised a system to protect certain bottom-of-the-bay scallops from the crushing jaws of cownose rays, while leaving others nearby vulnerable and monitoring whether the protected individuals survive at high rates. higher.

The system she devised is quite simple: a sort of corral, made of iron rebar welded into a square with the iron bars protruding about a foot from the bottom.

The idea is that the iron spikes will prevent stingrays, which are not particularly agile like finfish species, from reaching the scallops laying in the protective corral. Other native predators, such as spider crabs and whelks, that feed on scallops could still reach them the same way they would scallops outside the corral. So if a substantial difference is seen in scallop mortality near one of its corrals, cownose rays could be presumed to be the deciding factor.

“It’s a bit tricky because the rays come into the bay in large groups and we want something that would allow small predators in but exclude large predators,” MacGregor said. “Whelks and crabs should be able to crawl between the spikes, but rays not.”

To keep the scallops in the protection zone – unlike clams and oysters, scallops are quite mobile and can glide along the bottom of the bay pushing water through their shells – she ties them with small lengths of fishing line stuck to their shells.

As cownose rays are just beginning to burst into the Peconics — another Stony Brook research team is starting to tag dark brown rays with acoustic tabs so their movements can be tracked — MacGregor said she’s been watching the four sites where she installed the excluder device, experienced high mortality due to predation from other more common sources.

Spider crabs and whelks, which each leave telltale signature marks on the shells of scallops they attack, kill and consume, have proven to be aggressive and fast scallop hunters.

“It’s pretty crazy: we’ll put the scallops in and put them out and we’ll actually see the whelks start moving towards where we put them,” marvels MacGregor. “By the time we finish they are already moving to attack.”

She said that in as little as 24 hours, mortality rates for scallops placed for the experiment were as high as 50%.

Along with the predator experiment, MacGregor and his lab partners are also testing the other main theory for the ill fate of scallops: that they are overworked by environmental conditions, climate change and their own life cycle.

Since shortly after the first mass kill in 2019, the consensus mortality theory has been that scallops are stressed by water temperatures in the Peconic Estuary that now far exceed historical norms essentially every summer, for a new parasite that has been found in almost all bay scallops and, finally, the death knell, when they spawn and deplete their already depleted energy reserves.

“We look at everything, temperatures, salinity, dissolved oxygen, pH levels, which we can use to make inferences about mortality throughout the year,” said the New Jersey native and graduate. from the University of Maryland.

Just like a human being, a scallop under varying levels of stress, for lack of a better word, will breathe harder. The Stony Brook researchers therefore measure their breathing rate to determine how stressed they are by each change in conditions in the estuary during the summer. Testing a scallop’s breathing rate isn’t easy in the field, requiring contraption worthy of the praise of Rube Goldberg himself, complete with wires and cables, pumps and dials.

“We have some fun looks going across the canal in our little boat with all these wires and computers and a generator inside,” MacGregor said. “But we can take a scallop out of the bay and put it in a chamber and pump water through it and measure the oxygen uptake and make inferences about their stress levels. And we can do that throughout the year as the temperatures change and they breed in. We really see how they fare at any given time.

MacGregor, who expects to complete her master’s work here this year, says she hopes the work she began while at SOMAS will carry over into the work of the next class of researchers passing through the labs of Peterson and other SOMAS teachers. With local waters steadily warming in recent decades and little hope of that trend reversing, she hopes today’s research can guide tomorrow’s thinking.

“We are all under the influence of climate change and there is no stopping it now,” she said. “But hopefully we can inform policy, which will help curb climate change and perhaps restore our coastal systems.”

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