Environment

Our Bay: 10 things you didn't know about oysters

By PAMELA WOOD, Staff Writerr
The Capital, Published 02/13/10

Oysters are at the center of an intense debate over how to boost their population, how to manage the harvest and more.

Once the king of the Chesapeake Bay's seafood hierarchy, oysters have long since been dethroned by blue crabs. Past overharvesting, pollution and disease have taken their toll on this beloved shellfish.

But how much do you really know about the bay's native Eastern oyster, Crassostrea virginica? We tapped some of our experts to share little-known trivia about the oyster.

1. Oysters often change gender.

That's right, we've got gender-bending oysters.

"Young oysters tend to be male," said Chris Judy, an oyster scientist with the Maryland Department of Natural Resources. "Then, around 2 years old, most have switched to female. That's just the way the animal is."

The difference in genders is one reason why it's important to have oysters of a variety of ages on an oyster reef. If they're all young (or all old), reproduction will not work out very well.

In some cases, those older female oysters have switched back to the male gender to boost reproduction, said Stephanie Reynolds Westby, a scientist and "oyster wrangler" with the nonprofit Chesapeake Bay Foundation.

You can't tell the gender of an oyster just by looking at it, but scientists can tell in the lab.

2. To reproduce, oysters send their sperm and eggs out into the water.

Kids often ask how oysters can produce future generations, considering they can't move, Westby said.

Since oysters can't move, they do what's called "external fertilization," which basically involves expelling eggs and sperm and hoping they meet up and fertilize.

"They both have to get lucky," Judy said. "They have to find each other, fertilization has to occur in the wide expanse of the Chesapeake Bay."

Once fertilized, they turn into larvae that float and swim for about two weeks before attempting to attach to a new home permanently.

"If they're lucky, they land on something hard like an old oyster shell," Westby said. "If they're not lucky, they land in the mud and die."

3. Oysters are vegetarians.

And this is what everyone likes most about oysters. Oysters eat plants - and more specifically, they eat algae.

A single 3- to 4-inch oyster sucks in water at a rate of 2 gallons per hour. They use cilia on their gills to separate out the algae for nutrition.

This is a good thing, as it helps clear the bay and its rivers from algae, which can suck life-sustaining oxygen from the water.

Oysters aren't super-picky about which algae they eat. Judy from the DNR said he's put oysters in buckets with all kinds of algae, and without fail, the oysters gobble it up.

"I've seen them eat all kinds of algae in the bay ... I've never seen an oyster fail to clear the water," he said.

4. There's a history behind the closed harvest in the summer.

Watermen are banned from harvesting oysters in the warm months of the year, although oyster farmers can pull their oysters and sell them year-round.

The current reason for the summer no-harvest rule is that's the time when oysters are spawning and trying to create baby oysters.

It's best not to interrupt that process.

Before harvest managers knew about oyster biology, they knew oysters spoiled when they were shipped without refrigeration in the 1900s and 1800s.

"It just wasn't practical or safe from a public health standpoint," Judy said.

And before that, there was even another reason.

European settlers were familiar with their own oysters, which tasted gritty in the summer, so they weren't eaten.

Why were they gritty? European oysters reproduce differently - the egg stays in the female and is fertilized.

As the larvae developed into baby oysters, or "spat," in the summertime, that left a sandy, gross taste to the oyster.

And no one wanted to eat that.

5. Oysters can survive bouts of low oxygen.

A lack of dissolved oxygen in the water dooms many critters in the bay.

Oysters need oxygen, too, but they can survive short spells of low-oxygen conditions.

"Oysters can close up and they can live off of some of their stored energy," Judy said.

Out of the water, in cool temperatures, oyster can live for a week.

This also comes in handy when the water suddenly becomes too fresh or too polluted for oysters.

They'll occasionally open up to test the water to figure out when it's safe to get back to their normal business, Judy said.

"They can hunker down and stay closed up," Judy said. "We've seen this happen for a week or two. They can't endure this forever."

6. A raw oyster is likely still alive when you eat it.

Maybe you didn't want to know this.

But if your raw bar oyster is cool, it's technically still alive when you put a dollop of cocktail sauce or a squeeze of lemon on it and send it sliding down your throat.

"A raw oyster is a live oyster," Judy said.

If you touch the edge of the "meat" of the oyster with a fork, you might actually see it move a bit.

Oysters and other shellfish are perhaps the only type of food we eat while it's still alive.

7. Oysters were once a major part of the economy and the seafood industry.

In fact, oysters were such a big deal that watermen would literally have battles, known as the "oyster wars."

Maryland officials created the State Oyster Police in 1868 to enforce oyster harvesting restrictions.

Today's Natural Resources Police force is descended from those first oyster policemen.

Back then, the bay's oysters were known far and wide as "Chesapeake gold," said Westby of the bay foundation.

"They were shipped out to the nation through railroad cars," she said.

Until just a few generations ago, oystering was the prime moneymaker for watermen.

"Oysters were king," said Judy of the DNR. "Watermen made their real living off of oystering."

8. A typical oyster lives three to four years and reaches 3 or 4 inches in size.

The minimum size to harvest an oyster is 3 inches, and oysters grow an inch per year.

The bay and its rivers currently do not have ideal conditions for oysters, Judy said.

In salty areas to the south where oysters grow more quickly and reproduce well, the oyster-killing parasites MSX and Dermo are strong.

And farther north, there is less disease, but oysters don't survive and reproduce as well because of lower salinity.

In some places in between, oysters can live six to eight years and reach 6, 7 or 8 inches.

Famous Jamestown explorer Capt. John Smith boasted of oysters the size of dinner plates in the bay in the early 1600s.

The bay was in pristine condition back then, so that might not be too much of an exaggeration, Judy said - depending on the size of your dinner plate.

Oysters might have lived 15 to 20 years back then.

9. Oysters have complex organs.

An oyster doesn't look like much, basically a beige-colored blob inside two shells.

But oysters have a bunch of complex organs. They have gills, a mouth, a pre-stomach structure called a "palps," a stomach, a heart and more.

Oyster blood is virtually colorless.

"At first glance, you have a simple, almost rock-like animal and yet ... you just have an incredible amount of complexity," Judy said.

10. The City of Crisfield is built on a foundation of oyster shells.

Crisfield is a small city on the lower Eastern Shore best known for its annual J. Millard Tawes Crab and Clam Bake (a favorite of politicians) and for being the "crab capital of the world."

But much of the city was built on a foundation of oyster shells, including the municipal wharf.

(Revised February 2010)