The diversity of life on an oyster reef calls to mind the great coral reef of the Carribean. Photo courtesy Dave Harp.
Oysters: The Jewels and the Workhorse of the Chesapeake
By Kimbra Cutlip
Published in the Winter 2014 issue of Save The Bay magazine
Perhaps no other creature of the Bay can claim such a storied history as the Eastern Oyster. For centuries it was the bedrock that underpinned both the environment and the economy of the Chesapeake Bay.
When I moved to Maryland 20 years ago, oysters were just something I'd seen on a menu. But I landed in Galesville, a town that had thrived on the bounty of the Chesapeake. Signs of the oyster were everywhere, from the chalky, crushed shell driveways to the rusty gallon-sized cans bearing the label of Woodfield's oyster packing plant. I quickly learned that Crassostrea virginica, the stony jewel of the Chesapeake, defines the cultural heritage of this region. Until the 1980s, it was the most valuable fishery in the Bay.
Rising from the bottom, sometimes 30 feet to the surface, mounds of oysters once formed great reefs throughout the Chesapeake Bay and its tributaries. Currents passed over and around these reefs like wind around mountains, churning oxygen from the surface down into deeper waters.
Oysters at a Glance
ALSO KNOWN AS: The American or Eastern oyster.
RANGE: Bay oysters are found along the East Coast from the Gulf of St. Lawrence to the Gulf of Mexico.
REPRODUCTION: Females can produce upwards of 100 million eggs each year.
INTERESTING FACT: Oysters can change gender. In their early life, they are males, but by age two or three they become female and produce eggs. A single female can spawn 100 million eggs annually. Also, if a reef has very few males, or young oysters, female oysters can switch to become male-a characteristic called simultaneous hermaphroditism-and a sign of an unhealthy reef.
For 10 Things You Didn't Know About Oysters, visit cbf.org/oysterfacts.
Oysters become habitats serving as homes for sedentary critters such as mussels, sponges, and barnacles. The crevices between offer refuge to crabs and small fish. Larger fish gather to forage among the aquatic buffet.
It was this buffet that helped sustain the animals living within the Chesapeake for thousands of years. People, too, have depended on the oyster for survival. As they grow, oysters build layers of calcium that form a record of the conditions in which they lived. They tell us about temperature, salinity, and oxygen levels. For instance, we know from written accounts that oysters nourished the settlers of Jamestown during "The Starving Time." But it's the record written in shells that tells us the colony had been suffering under the worst drought in 800 years.
Today, the oysters that grew in abundance when the early colonists arrived are recovering from near obliteration. Over harvesting during the late 1800s and early 1900s nearly scoured the bottom clean. By the 1920s two-thirds of the reefs were decimated. Near the end of the century, disease and pollution depleted oyster populations even further. The number of these crucial shellfish plummeted to a scant few percent of what it was when Captain John Smith first explored the Bay.
In the last two decades, there has been a growing movement to restore oysters in the Bay. CBF has planted more than 200 million oysters in Maryland and Virginia waters. Our volunteer oyster gardeners play a big role in keeping up supply. We give them baby oysters, which they grow in cages hanging from piers. A year later, the gardeners bring us their full-grown oysters for planting on sanctuary reefs. For the most part, those reefs are the same flat bars and beds people have come to associate with oyster habitat. But that's not the natural topography of the Bay.
We now know that in order to thrive, oysters need more than a hard surface on which to attach. They need vertical scaffolding that allows them to grow up above the muddy bottom. They need a world of three dimensional structures where currents swirl around obstacles, mixing oxygen into the water and carrying away silt. Natural reefs once furnished all of that.
Efforts to restore the jewels of the Chesapeake face a unique challenge. "The fewer oysters you have, the fewer places you have for oysters to grow," said Karl Willey, Manager of CBF's Maryland Oyster Restoration Center. Without reefs, it's a desert down there."
What's more, the vital habitat reefs provide is just part of their contribution to the Bay. Each adult spends its life filtering pollution from the water at a rate of up to 50 gallons per day. On the half-shell, the bivalve may look like a creamy grey lump of meat, but it's actually an anatomical marvel built of pumps and filters. As currents flow past four rows of gills, tiny hairs filter bits of mud and sand from the water. The hairs wave lighter particles such as microscopic algae (phytoplankton), bacteria, and bits of decayed material up toward the oyster's mouth. Yes, they have mouths. They also have sensory nerves that taste everything before it enters the mouth. Anything that doesn't pass muster gets wrapped in mucous and spit out. Through this remarkable process of eating, bivalves clean the water.
When oysters were plentiful, they could filter the entire volume of the Bay in four days. With so few remaining today, the job takes about a year. In addition, the diverse community of filter feeders that live on a healthy reef have their own role in cleaning up the water.
For all of these reasons, oysters are essential for a healthy Bay.
It would take thousands of years to regrow the reefs that have been destroyed. But another solution offers literal relief for the beleaguered oyster population. Reef balls, concrete structures resembling large whiffle balls sliced in half, introduce instant three-dimensional structure on the bottom of the Bay. Like the nooks and crannies of a natural reef, holes in reef balls make the perfect home for fish and other critters that live naturally among the oysters.
CBF has planted thousands of reef balls throughout the Bay, each covered with thousands of juvenile oysters. In the Choptank River, the three-dimensional habitat created by reef balls and other reconstructed reefs has attracted black sea bass, spade fish, and other species that haven't been seen in Maryland waters for many generations.
Some groups have expressed concerns, however, that artificial reefs pose a hazard for navigation and crabbing. But the benefits of healthy reefs and a thriving underwater community will pay off for everyone.
Still, reef restoration is only part of the solution. Water quality poses another challenge. Rain washes pollution from the land into the Bay. Mud and dirt can bury oysters living on the bottom. At the same time, runoff from fertilizer and waste causes blooms of algae that eventually die and decay. The process removes oxygen from the water, suffocating oysters.
Oysters are a complex and integral part of a healthy Chesapeake Bay. Their demise has come at a great cost to the environment and the economy of the region. But we know how to restore them. Reducing pollution and rebuilding reefs will help oysters survive in significant enough numbers to become self-sustaining. The oysters in turn will help clean the water and return a dynamic three-dimensional landscape to the bottom of the Bay. It took a few centuries to get us where we are today. It will take a long time to return to days of plenty. But it can be done. The story of the oyster's recovery will be the story of a cleaner Chesapeake teeming with underwater life.