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Florida oysters are a lot smaller than they used to be. Climate change may be the reason

A new study of ancient oyster shells in Crystal River finds some as big as 7 inches.

Florida’s oysters used to get a lot bigger than they do now.

In prehistoric times the oysters found in the Crystal River area would grow up to 7 inches long, according to a new study published today. Now their maximum size is more like 4½ inches, the study found.

“There has been a dramatic change in their size and structure,” said Gregory Herbert, a paleobiologist at the University of South Florida who was a co-author on the study.

While the scientists can document that the shrinkage occurred, what they don’t know is why. One suspect: the warming Gulf of Mexico water thanks to climate change. As the temperature of the water increases, the amount of oxygen declines, which would affect the size of the oysters, they said.

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But other factors could play a role, too, they said. For instance, in the late 1800s the watershed around Crystal River changed as new farms, new mines, new railroads and new houses, stores and hotels were built, prompting lumber companies to hew down the forests. That, too, could alter the water chemistry in the region.

The bottom line, though, is that Florida’s prehistoric inhabitants enjoyed “a range of oyster size that no longer exists today,” said Stephen Hesterberg, another USF scientist who worked on the study.

The study, published Wednesday in the publication Biology Letters, originated when one of the USF professors was chatting with some graduate students and found out that his ongoing research project involving the ancient oyster shells at Crystal River paralleled research being done by other scientists. They decided to join forces.

Florida’s shoreline tends to grow Eastern oysters (Crassostrea virginica), which are found from the Yucatan Peninsula in the Gulf of Mexico to the St. Lawrence River in Canada. They are among Florida’s top commercial seafood products.

Oysters are more than just a great appetizer served with a slice of lemon and some cocktail sauce, though. They clean the water, too. A single oyster can pump and filter 25 gallons of water in 24 hours.. Oyster reefs also help stabilize the coastline and provide habitat for fish, shrimp, crabs and other animals.

Although the scientists have explored the chemical composition of the shells and how the ancient ones contrast with the modern ones, they do not know whether the change in size is a permanent genetic adaptation or if it can be altered.

They hope that further research will help them figure that out. If the shrinking of the shells is reversible, they hope to provide a guide for how to bring back the big oysters of prehistoric days.

This story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative founded by the Miami Herald, the South Florida Sun Sentinel, The Palm Beach Post, the Orlando Sentinel, WLRN Public Media and the Tampa Bay Times.