Puget Sound has more armor than the Tower of London — 600-plus miles of concrete, rock and timbers enclosing about 26 percent of its total shoreline. And it’s still spreading: According to data collected by the Washington Department of Fish and Wildlife, a little over a mile of concrete and riprap gets laid along the Sound each year, 76 percent of it on residential property. This trend may accelerate as climate change proceeds and sea levels rise, spurring waterfront owners to seek more protection.
Bulkheads and beach berms disrupt shore currents and block natural beach replenishment, which starves intertidal zones of sand, gravel and sea wrack. These zones are essential incubators for forage fish such as sand lance and surf smelt, and feeding grounds for young salmon, and armoring is widely thought to be dreadful for them. “It’s really death by a thousand cuts,” says Randy Carman, who manages DFW’s near-shore section and monitors the spread of bulkheads.
Nevertheless, good, hard local data on armoring’s habitat effects have until now been lacking. In that absence, often contentious debates have flared for years between environmentalists and scientists eager to restore, or at least preserve, natural beaches, and affluent landowners who fear their waterfront villas will wash away.
Megan Dethier, a biologist at the University of Washington’s Friday Harbor Marine Labs, would like to change that. (Disclosure: Dethier gets funding from Washington Sea Grant, a marine research and education program that I work for.) She’s undertaken the elusive task of documenting the ecosystem effects of shoreline armoring on Puget Sound. Elusive, she explains, because “it’s trying to look at a process that takes decades. Funding organizations don’t tend to provide money for a study taking longer than two or three years.”
Those impacts have been studied and confirmed in Europe, New England and Hawaii, where studies conducted over many years, taken together, provide the long view needed. “As naysayers are quick to point out, conditions are very different here,” says Dethier. And there have been “surprisingly few” studies documenting impacts in this region.
Dethier decided to beat the clock and compress that process by comparing conditions at 31 pairs of neighboring beaches, 25 in West Seattle and elsewhere on Central Puget Sound and six on the South Sound. One beach each pair was armored, the other not; together they reveal effects accruing over decades.
For three years, Dethier and her colleagues have surveyed the beaches’ topography and overhanging vegetation, measured their sediment grains and deployed wave gauges. They’ve tallied washed-up logs and wrack, the insects, crustaceans and worms dwelling amid them, and the abundance and types of juvenile clams in the low shore. To unravel what this means for the food web, graduate student Sarah Heerhartz (at left) snorkeled the Central Sound sites counting juvenile salmon and recording their behavior. She’s also developed studies (still underway) to quantify beach use by land birds. Spoiler alert: Fewer birds appear to congregate on armored beaches, and they use them differently.
Dethier and Heerhartz have submitted two papers for publication, on the relative abundance of the organic debris called “wrack” on armored and natural beaches and on how young salmon behave along those beaches. They’re still working on a third paper, which will look at insects and other invertebrates there.
They haven’t found differences in grain size or clam abundance at mid-shore levels, though Dethier cautions that impacts may yet occur in the longer term. Further up, they found slightly steeper foreshores on armored beaches and coarser sediments — a concern for surf smelt and other forage fish that spawn there. The armored beaches also had less riparian vegetarian and substantially fewer logs (important as wave buffers and habitat), as well as less of the sea and terrestrial wrack — seaweed and leaves, respectively — that shelters the invertebrates on which fish and birds feed.
Like what you just read? Support high quality local journalism. Become a member of Crosscut today!