Climate

The Best Defense Against Sea Level Rise Leaves Little Room for Birds

The seawalls that fortify our coasts against rising seas also degrade bird habitat. But there are few good solutions unless people retreat inland.

Karl Nordstrom has grown used to seeing a world invisible to everyone else. When he goes to the Jersey Shore and gazes upon an endless stretch of white sand, he doesn’t see the pinnacle of natural beauty like most beachgoers. Rather, he sees a human invention—“a recreation platform,” as he calls the raked white beaches at coastal resorts and summertime shore towns.

“If you’re looking at the beach every summer—if you go out there, and it’s practically graded flat, and there’s no vegetation on it—you begin to think that’s what the beach is supposed to look like,” he says. “If the beach always looks the same, you lose sight of the fact that it’s dynamic. The whole thing is dynamic.”

A coastal geologist at the Rutgers School of Environmental and Biological Sciences, for 40 years Nordstrom’s studied the natural evolution of beaches—how waves erode and reform beaches on daily and seasonal cycles, and how those natural cycles create hill-like dunes that support wildlife and protect inland areas from storms and flooding.

For decades coastal towns have called upon his expertise as they prepare for sea level rise and the stronger storms that come with it. Rising seas related to climate change are eroding beaches and pushing inland, endangering homes and property that were once considered safe. But people rarely take Nordstrom’s advice, which is to abandon their homes and retreat from the coast. “If you can see the sea, the sea can see you, and you’re at great risk,” he says.

Instead of moving, homeowners and communities are resorting to coastal protection plans that offer an appearance of safety but no guarantee. Some towns are trucking in sand to replenish eroded beaches and build artificial dunes. But more often than not, people are building seawalls in front of their homes and behind beaches. Often 20 feet tall or higher, these concrete behemoths are constructed to withstand the sustained assault of incoming waves and storm surges. Seawalls currently line 14 percent, or nearly 15,000 miles, of the United States coastline—a number that’s expected to grow in the coming decades as the sea level rises.

As construction intensifies, a growing chorus of scientists and environmentalists are raising concerns over an unintended consequence: Seawalls eliminate habitat for birds and other wildlife. Their footprints take up space on the beach the day they're built. Then, over the course of decades, beaches in front of seawalls often narrow when natural cycles of erosion and sand deposition are disrupted.

Even before seawalls fully erode beaches, they drive wildlife from the area, according to a study published last month in Bioscience. The analysis pooled data from 25 studies about seawalls, and found that half as many organisms and a quarter fewer species live on beaches and marshes in front of seawalls compared to seawall-free areas.

No group of animals reacted more strongly than birds. In one stand-out study, Jenny Dugan, a coastal ecologist with the University of California’s Santa Barbara Coastal Long Term Ecological Research Project, counted more than 6,800 birds along three miles of Santa Barbara’s beaches over the course of a year. The beaches were identical except that some had seawalls and others didn’t.

Scientists counted four-times as many Double-crested Cormorants on unarmored beaches than seawalled ones. Photo: Eric Stogner/Audubon Photography Awards

On the beaches in front of seawalls, she saw one-third as many shorebirds and one-quarter as many gulls and cormorants—an undeniable trend. “It was completely different for the birds between armored and unarmored [beaches],” Dugan says. “It was a very clear signal for us.”

Birds avoid seawalls for a simple reason: They need dry sand, which is often lacking on the eroded beaches in front of seawalls. In her study, nearly every beach in front of the 80-year-old seawalls lacked dry sand. Without that dry sand zone, birds don’t have refuge from the waves as they forage in the surf. They also lose an important food source. Dugan found 15 times as many tiny invertebrates—shorebird food—on beaches without seawalls.

“Once you lose that [dry sand zone], you lose all that biodiversity,” Dugan says. “That’s the food that’s available to birds during high tides. It’s a big part of the food web." 

What makes this loss of habitat even more unsettling for researchers is that it might not be necessary. The effectiveness and practicality of seawalls is often debated. In some cases, they have saved towns from crushing floodwaters, but in others, they have failed catastrophically. Seawalls also require constant upkeep; with each wave, the concrete slowly weakens and crumbles. And as sea level rises, what was once a tall-enough wall may not provide enough protection.

“Seawalls will not last forever," Nordstrom says. "They’re considered a permanent solution, but they’re not. They are the last-ditch defense if there’s nothing else you can do.”

In Nordstrom’s ideal world, people would retreat from the coasts, leaving the beach to serve as a buffer zone to protect inland areas and as habitat for birds and other wildlife. “That’s definitely better than a seawall,” he says. After decades of pleading, though, he’s had to accept that coastal retreat isn’t going to happen any time soon. 

To make the best of a bad situation, Nordstrom now advises coastal homeowners to combine defensive seawalls with habitat restoration. “If you must have a wall, put that wall as close to human infrastructure as you can and let nature be in front of it,” he says. And piling sand on top of a seawall can create a reinforced dune while providing habitat for wildlife. Nordstrom also encourages people to plant native dunegrasses and shrubs on their lawns as well as on beachfront sand. If they take his advice, before long those raked white beaches may well look more like the dynamic natural habitats they are meant to be. 

“Appreciate the coast for more than just sand and sun and blue water; appreciate it for the way it evolves and grows, and is eliminated and comes back,” Nordstrom says. “That’s part of the cycle of nature. Texture, typographic diversity, change—embrace it.”

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