What can you do when breakwaters break?

Waterfront property owners have long been common practice to build offshore reefs or seawalls out of stone, concrete, or wood to keep wind-driven waves from eroding their shorelines. But storms have worn down many of those breakwaters over the years, and the rising sea level is gradually compromising even the sturdiest of them.

Amanda Poskaitis of the National Wildlife Federation and Matthew Gray of the University of Maryland put “oyster castles” together on an old breakwater in Maryland’s Choptank River. Credit: Dave Harp / Bay Journal Media

Repairing or replacing failing breakwaters can be costly and temporarily disrupts submerged grasses and bottom-dwelling marine creatures.

Now, researchers with the University of Maryland Center for Environmental Science, working with the National Wildlife Federation, are trying out a greener, potentially less pricey alternative. They’re topping those eroding structures with “oyster castles,” interlocking concrete blocks seeded with bivalves that can be put together to mimic natural oyster reefs.

“[There are] hundreds of breakwaters throughout the Chesapeake Bay,” said Matthew Gray, an oyster researcher at UMCES’ Horn Point Laboratory in Cambridge, leading the effort.

An oyster-encrusted castle placed atop an old breakwater nearly breaks the water’s surface in an inlet off Maryland’s Choptank River. Credit: Dave Harp / Bay Journal Media

He said some of those wave barriers have already been battered down and submerged beneath the water’s surface. And with some studies projecting 2 feet of sea level rise by 2080, many more are likely to be drowned and rendered ineffective in coming years.

“So if this works,” he added, “that’s a way we could green the gray infrastructure and prolong its effectiveness.”

Oyster castles are being tried in several places as part of “living shorelines,” more plant– and wildlife-friendly alternatives to the bulkheads or stone revetments often used to armor the waterfront against erosion. Using them to rehabilitate failing breakwaters presents new opportunities — and challenges.

Standing waist-deep in water, Iacopo Vona, a graduate research assistant at Horn Point, struggled to keep his footing as he hefted an oyster-encrusted block from an idling motorboat. With a splash, he plunked it atop a submerged pile of rocks that years ago had been installed as a breakwater at the inlet to a shallow cove off the Choptank River.

“No guts, no glory!” called Richie Long, the laboratory staffer piloting the boat, as Vona lost his battle for balance at one point and went down in the water.

Soaked but undeterred, Vona and others on the research team labored the next two days until they had placed about 60 oyster castles on the uneven bottom, layering them high enough to break the surface of the water.

The project is underwritten with a pair of $50,000 grants — one for design and development via the National Fish and Wildlife Foundation and the other for the actual work, from the Palmer Foundation, a private nonprofit named for the first president of Snap-on Tools.

“It took a lot of effort for just a small little patch,” Gray said, “but this is kind of a brand-new project, and we were figuring it out as we [went].”

University of Maryland researcher Matthew Gray works on an “oyster castle” in Maryland’s Choptank River. Credit: Dave Harp / Bay Journal Media

The first challenge they faced was to level the uneven ridge of the deteriorating breakwater. The blocklike castles must be set on a flat surface to fit together properly. So the researchers tried filling the gaps by emptying pails of crushed stone water over them. It worked, after a fashion, though the team is still mulling whether they need to anchor the castles to secure them against storms better.

“Almost miraculously, it fit together on that particular breakwater system,” said Amanda Poskaitis, Mid-Atlantic coastal resilience program manager for the National Wildlife Federation. The Virginia-based conservation organization has partnered with UMCES on the project because they hope it will be useful not only throughout the Bay but in coastal areas elsewhere.

Researchers will study the rebuilt breakwater’s effectiveness at dampening wave energy. But they’re also anxious to see if the oysters clinging to the castles survive and multiply, so they can do at least a bit to help clean up nutrient pollution in the Chesapeake Bay.

Lab tests have shown that when the concrete castles are covered with bivalves or other filtering organisms like barnacles, they pull nitrogen from the water at “exceptionally high rates,” said Jeffrey Cornwell, a research professor at Horn Point who’s studied the nutrient removal capabilities of oysters.

The overall nutrient removal of these castled breakwaters will be relatively limited, Cornwell cautioned, because they’re not likely to occupy a large portion of the Bay and its tributaries. But if significant filtration rates can be verified in the field, he added, that could make it worth offering financial incentives to waterfront property owners or others needing pollution removal credits for enhancing breakwaters this way.

Matthew Gray and Richie Long, both of the University of Maryland Center for Environmental Science, look on as Iacopo Vona, a graduate research assistant, grapples with an oyster-encrusted concrete block on an old breakwater in Maryland’s Choptank River. Credit: Dave Harp / Bay Journal Media

Another limitation for such projects in Maryland may be the state’s cold winters. Oysters die if exposed to freezing air temperatures, so bivalves on castles that project above the water at low tide are at risk. But Gray pointed out that the castles used to build the pilot project had large oysters that had survived because the past few winters had been relatively mild.

That vulnerability won’t be an issue farther south, Poskaitis noted, where freezing temperatures are rarer. For that reason, she said, she expected these breakwater enhancements to work even better along the Carolinas coast.

“Of course, [with] some breakwater systems, it’s not going to work,” she added. “But we think that using different types of oyster structures could be a way to increase habitat and resiliency in offshore breakwaters.”

Tim Wheeler is the Bay Journal's associate editor and senior writer, based in Maryland. You can reach him at 410-409-3469 or twheeler@bayjournal.com.

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