After spring rains, a reign of oysters

Last spring's Mother's Day deluge may have turned parts of the Bay State into federal disaster areas, but it may also have been the force behind some good news coming out of New Hampshire's Great Bay this fall.

Baby oysters, millions of them, are fixed to the bay bottom in numbers not seen since scientists started tracking them almost 30 years ago. The discovery was made during underwater surveys in the fall. Scientists will be spending the winter trying to find out what caused this bounty of the bivalves in the pristine wetlands that border Newmarket, Greenland, and the Pease International Tradeport.

"This is not a trivial event; there are more oysters out there than there have been for a long time," said Ray Grizzle, leader of a state effort at the University of New Hampshire to restore oysters to Great Bay.

"We've got as many as 2,000 young oysters per square meter out there," Grizzle said. "That's over 10 times what we get in a good year. This is unprecedented in our record books."

Those books go back to the early 1980s, when the once-expansive Great Bay oyster beds started to die off in huge numbers -- due, scientists believe, to diseases caused by water-borne bacteria. To counter this trend, Grizzle has been raising disease-resistant oysters and seeding them throughout the bay for the past few years.

But disease resistance is not the first explanation experts are offering for the oyster explosion, according to Doug Grout, a supervisor of marine programs with New Hampshire's Fish and Game Department. The search for explanations has instead turned toward a more natural cause: rain, and lots of it.

About 12 inches of rain fell over the May 14 weekend, followed by another 2.5 inches on June 7. All that fresh water washing into Great Bay may have given the baby oysters naturally spawned last year an important edge in a critical period of their development, Grout said.

Great Bay oysters produce millions of larval offspring each year, but almost all die in the first few months of life. Those that survive into the following winter are called a set, and this year's set is phenomenal, both men said.

All that rain water may have killed off predators, like green crabs, that eat baby oysters. It's also possible the fresh water kept the oysters from opening up and feeding for a few weeks last spring, thus making them less vulnerable at a critical time in their early lives, Grout said.

"We had tremendous amounts of fresh water come into this estuary," he said. "The salinity in the bay was very low for prolonged periods of time. So, maybe this set has something to do with these oysters not opening up then. Right now, it's all speculation, but we intend to look into it."

Keeping track of the set produced from the larval oysters each year has been an important part of the restoration efforts. Each year divers count the oysters found in 1-square-meter "quadrants" marked off in select areas of the bay's known oyster beds.

In 2002, divers counted an average of about 300 baby oysters -- also called spat -- in each quadrant, in what was then one of the best years to date, Grizzle said. This fall, the numbers averaged 1,500 to 2,000 spat per quadrant.

"The bottom line is, this year was about ten times higher than anything we have seen so far," Grout said.

This would not be the first time natural disaster has produced a bumper crop for salt marsh shell fish, according to Grizzle. There have been huge set s of hard clams in Florida following big storms there, and this could be a similar sort of dynamic, Grizzle said.

Oysters were once the keystone of Great Bay's estuarine environment. The oysters have historically helped clean the bay water, by filtering out microscopic plants and animals called plankton.

They also filter out a lot of the sediment that muddies the water. And clear water is crucial to growing a form of seaweed called eelgrass, a building block of East Coast estuarine ecosystems. Fear that the eelgrass could disappear from Great Bay has made restoration of the oysters a top priority for environmentalists at UNH and the Fish and Game Department.

Right now the oysters are about the size of an average thumbnail. If they succumb to disease, it's usually in the first few years, said John Nelson, marine fisheries division chief for the state agency. If this set does survive to adulthood, it could bode well for the future of the Great Bay oysters.

"There's always that possibility that we have a strain that is resistant to disease out there now," Nelson said. "We won't know until three or four years from now."