Even prior to the oil spill, decades of over-harvesting, disease, pollution and declining habitat have decimated the massive oyster reefs that once dominated the country’s coastal estuaries. Globally, 85 percent of reefs have been lost, making oyster reefs the most severely impacted marine habitat on Earth.
Because oyster reefs are essential to a healthy marine system, The Nature Conservancy has been experimenting — from North Carolina to Texas — with techniques that may provide hope for the oyster’s future.
“While some of these projects are on hold due to the oil spill, our work is now undoubtedly even more important to help the Gulf of Mexico heal,” said Rob Brumbaugh, coastal restoration director for the Conservancy.
“Meanwhile, there may be a temptation to increase harvest pressure on reefs not affected by the spill – in the Gulf and beyond – to make up for decreased oyster production,” Brumbaugh continued.
“Given the magnitude of oyster reef loss globally, however, and the importance of the impacted reefs, we need to be increasingly thoughtful about how to balance these near-term pressures with longer-term goals.”
An Ancient Ritual of Survival
When coastal water temperatures rise each spring, an ancient spawning ritual begins. Mature female oysters release millions of eggs; the males release an even greater number of sperm. Nature takes its course as fertilization occurs in the open water. The result? Microscopic oyster larvae that look like specks of black pepper.
These larvae soon develop a shell and feed on algae, drifting on currents and riding the tide. If they are lucky enough not to become fish food by the third week, they attach themselves to a hard surface — usually other oysters — where they transform into a tiny oyster called spat and bond with others to form a reef.
As oyster reefs decline, though, larvae have a slim chance of finding a suitable surface.
The Humble Oyster as Ecosystem Engineer
Just as coral reefs are critical to tropical marine habitats, oyster reefs are the ecosystem engineers of bays and estuaries. They provide important services to people and nature by:
- cleaning water – a single oyster can filter as much as 50 gallons per day;
- providing food and habitat for a diversity of plants and animals, including fish, crabs and birds; and
- serving as natural coastal buffers from boat wakes, sea-level rise and storms.
A System Out of Balance
Southern coastal communities feel the impact of oyster reef loss. In North Carolina’s Albemarle-Pamlico Sound, oyster habitat is down by 50 percent while the rate of coastal erosion can be as much as 45 feet per year. Along the Gulf Coast, devastating hurricanes have severely degraded estuarine and beach habitat, making an already fragile coastal system even more vulnerable to future storm activity.
Attempts to protect coastal areas from storms, increased wave activity and rising waters have usually involved the construction of hard structures like rock jetties, bulkheads and seawalls. But scientists have learned that these artificial barriers do more harm than good.
Not only do they reflect wave energy back into the water, causing additional loss of habitat, the structures also disrupt the ecological balance of the ecosystem.
“Hardened structures cut off the marine habitat from the rest of the ecosystem, disconnecting marine life from marshes along the margins of our estuaries and bays,” said Brumbaugh. “It’s similar to putting a dam in the middle of a river that prevents salmon from swimming upstream.”
Growing a Natural Solution
Oyster reefs, a natural component of the marine environment, are an alternative solution to the concrete and steel bulkheads that line some coastlines. Conservancy scientists throughout the South have been working with partners and experimenting with ways to create new reefs. The following are some highlights.
In Alabama's Mobile Bay, where 30 percent of the shoreline is now armored with bulkheads, scientists are testing three techniques to create 3 acres of oyster reefs and protect 10,000 feet of shoreline. One method — interlocking rectangular cages made of welded steel with space for mesh bags of oyster shells — is being used along Alabama and Louisiana shores after proving highly successful at Clive Runnells Family Mad Island Marsh in Texas.
Along Jeremy Island in South Carolina, scientists are constructing “oyster castles” made from interlocking blocks of concrete, limestone, crushed shell and silica. Meanwhile, Georgia researchers are testing the effectiveness of bagged oyster shells and chain link baskets made of welded steel and filled with rock and shells.
“One reason the techniques vary from place to place is that the threats vary,” Brumbaugh offered. “In Florida’s Indian River Lagoon, for instance, we lay oyster mats in the water that are specifically designed to work in the face of boat wakes.”
Rising sea levels — 2 inches per decade along the Albemarle Peninsula in North Carolina — spurred an effort to create four oyster reefs using 600 tons of limestone marl in Pamlico Sound.
In Mississippi and Texas, high pressure hoses were used to blow several tons of loose shell off barges to create oyster reefs in the Gulf of Mexico to enhance fish habitat and absorb the impact of hurricanes and tropical storms.
In South Carolina, scientists are testing the efficacy of "oyster castles" — concrete, shell, and limestone blocks — assembled on the shoreline to grow new oyster reef. They've also launched a pilot project to use loose fossilized oyster shell deposited in a managed wetland to see whether it is successful in growing reef.
“Conservancy scientists are trying a wide variety of new restoration methods,” Brumbaugh continued. “These will create better solutions — workable solutions — to problems like erosion, sea-level rise and today’s intense storms. We always strive to ensure that our solutions preserve the natural functions of the habitat.”