Restoring Oyster Reefs

“He was a brave man that first ate an oyster.” - satirist Jonathan Swift (1667–1745)

No one knows who that brave soul was who first shucked an oyster, but we do know that by the late 1800s millions of pounds of salty, slimy oyster meat were being harvested from places like North Carolina’s Outer Banks and shipped across the country. The secret was out: raw, steamed, grilled, or fried, oysters were on the menu from coast to coast.

As the demand for oysters increased, fishermen began using more sophisticated tools -- like mechanical dredge boats -- to boost their catch. And boy, were they successful! Marine scientists generally place the current oyster population at around 50 percent of what it was a century ago. And some estimates claim areas like North Carolina’s Pamlico Sound are at 10 percent of the levels that existed in the early 20th century.

One of the reasons that populations have been so decimated and haven’t been able to come back has to do with the habitat needs of the oyster. Baby oysters, or spat, literally grow on the backs of their ancestors. Spat swim in the water column until they can latch on to a suitable surface. More often than not, that surface is an established oyster reef made up of generations of older oysters. As wild oyster harvesting increased, the reefs diminished and baby oysters had no place to anchor. The oyster population plummeted.

But this isn’t just another “species of special concern” story.

It turns out that oysters are indispensable to the marine ecosystem. Aside from their role as a viable fishery, oyster reefs provide three main ecosystem services. They stabilize shorelines by breaking up wave energy, they provide habitat for hundreds of marine organisms such as crabs and barnacles and, perhaps most importantly, they help filter the water.

Adult oysters can filter up to 50 gallons of water a day. In this one hour timelapse video, you can see a decrease in the levels of turbidity, or murk, in the water.

Filter-feeding oysters transfer nutrients (including nitrogen) from the water to the bottom. That’s a good thing, not only for the marine ecosystem but also for humans. Studies estimate that oyster-reef sediments remove 25 percent more nitrogen than areas without oysters. An excess of nitrogen in the water promotes algal blooms that shade underwater vegetation and can lower the dissolved oxygen levels. Loss of underwater vegetation and low oxygen are increasingly common in coastal ecosystems. They can result in undesirable impacts ranging from reduced water clarity to fewer fish.

In North Carolina, and around the country, initiatives to restore oyster reefs can become a political, cultural, environmental, and economic quagmire. There are many competing interests at stake, from the livelihood of fishermen to government oversight to downstream water-quality issues. Scientists have long studied the many ecosystem services provided by oysters and are now stepping into the fray armed with data to prove where, why, and how to restore oyster reefs.

These days, the brave ones aren’t those eating the oysters. Rather, they are the men and women charged with keeping oysters in our waters and on our plates, now and into the future.