Illustration by Chad Lewis

Fish Below Your Feet and Other Solutions for a Living Harbor

In Seattle, Singapore, and other waterfront cities around the world, engineers are creating life-enhancing designs to encourage marine biodiversity.

I’m swimming under a sidewalk. The cantilevered slab of concrete is a couple of meters over my head, part of Seattle’s Central Waterfront area that is famous for Pike Place Market and the tourist stroll of chowder houses and souvenir shops. It’s not your average sidewalk: it’s been embedded with translucent glass bricks that allow light to hit the seawater. Like many of the other enhancements to the recently rebuilt sea wall, it’s an act of eco-engineering intended to improve marine habitat in the waters of Elliott Bay, in Washington State.

Thanks to the glass bricks, I can see some of the other subsurface innovations. Most obvious is what’s right in front of me: the concrete face of the sea wall itself, which has a cobbled, river stone texture and angled shelves that encourage the growth of algae and invertebrates. Below me, the seafloor has been built up with mesh bags stuffed with rocks, known as marine mattresses; these reduce the water depth and make the sea wall area more hospitable to juvenile salmon, which are evolutionarily programmed to prefer shallow, nearshore waters. As for the light-delivering sidewalk, it’s intended to boost seaweed growth and create a more inviting passage to shade-avoidant salmon smolts.

It’s mid-September, still technically summer. Bobbing in a drysuit and snorkel in the polluted waters of Elliott Bay would not usually be my first choice for ocean recreation, but I’m tagging along with two University of Washington (UW) habitat biologists who are counting fish and other marine creatures near the sea wall to see these enhancements close-up. They’re all elements of the US $688-million Central Waterfront redesign and, together, they help create habitat that more closely mimics a natural shoreline. This includes niches, hidden surfaces, shadow, sunlight, and micro-currents that promote the growth of the tiny organisms young salmon feed on—and shallower waters that provide juvenile fish greater safety from predators.

While the improvements may sound humble, they’ve made Seattle a pioneer in a growing trend: cities that want to have their sea walls and their sea life too.

Sea walls have been around for as long as there have been cities built near the ocean. Some of the earliest-known sea walls were built in Byzantium (later Constantinople, now Istanbul) in the second century CE. There might not be a need for sea walls if humans built their homes 10 kilometers or so from the sea. But we don’t. Besides a love of waterfront views, one of the more obvious factors in our need to congregate on the coast is our use of ships for trade and transportation, and the need for infrastructure to receive them and their cargo.

Researcher Jason Toft snorkels at Seattle waterfront
In Seattle, Washington, researcher Jason Toft snorkels under a new engineering solution to create salmon-friendly harbor front—a transparent sidewalk. Photo by Grant Callegari

Whatever the motive, humans continue to build close to the ocean, and sometimes—as with most of Seattle’s waterfront tourist attractions—right over top of it. Constructing barriers, like sea walls and breakwaters, is essential to protect architecture from extreme tides, waves, and storm surge (where winds drive seawater onto land at levels far above normal high tide). Left alone, coasts constantly change shape. Cities build barriers to control the shoreline—to keep erosion at bay and their infrastructure intact. Recent extreme weather events, like hurricanes Katrina and Sandy that hit New Orleans and New York City, have shown the devastation very large storm surges can wreak upon coastal towns and cities. In some areas, Hurricane Katrina’s surge was over eight meters high and reached inland over 19 kilometers.

The trouble is that coastal armoring almost always comes at a cost for marine species, juveniles and otherwise, that depend on natural shorelines.

Jason Toft, 47, is a senior researcher at UW’s School of Aquatic and Fishery Sciences (SAFS). He has conducted creature counts on Seattle’s waterfront for over 15 years. Sparked by the city’s recognition in the early 2000s that its downtown shoreline needed habitat improvements—resulting in a small beach near Olympic Sculpture Park created in 2006, and construction of the new sea wall that began in 2013—SAFS has embarked on a long-term effort to track the effects of the new sea wall on marine organisms. Gripping plastic clipboards and pencils in their neoprene-gloved hands, Toft and his colleague have spent the past hour snorkeling along the sea wall, scrawling observations—fish and crab numbers, notes about feeding behavior—on waterproof paper.

Among other species, today’s tally turns up 468 shiner perch, 57 striped sea perch, 16 red rock crabs, four kelp crabs, and two juvenile chinook. The low number of salmon seems alarming, but Toft says it’s typical for this time of year: their numbers spike in June and then decline as the majority of smolts migrate to the ocean. The number of shiners is also typical. “Down here, perch are like wallpaper,” he says.

A transparent sidewalk allows pedestrians a glimpse of life under their feet, and salmon a better chance of finding food. Video by Grant Callegari

About two kilometers south of the Central Waterfront lies the mouth of the Duwamish River. For millennia, the salmonid species that spawn here—including chinook, chum, and coho—used the Elliott Bay shallows as rearing habitat. Much of this was destroyed by the shoreline armoring that began when settlers arrived in the mid-1800s. Since then, development has transformed roughly 68 percent of Seattle’s foreshore. The increasingly artificial shoreline was part of a long series of blows—along with overfishing, pollution, and spawning ground degradation—for Seattle’s salmon population, and for the Duwamish people who depended on them.

Puget Sound chinook migrate into Canadian waters and range as far north as Alaska, and like other populations, are the primary food source for southern resident killer whales. The impacts noted above have reduced the historical populations of Puget Sound chinook by at least 90 percent, landing them on the endangered species list in the United States. Seattle’s willingness to invest in translucent sidewalks, cobbled surfaces, and marine mattresses has largely been a response to the desperate situation facing Puget Sound chinook.

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