Jeff Cordell and Erin Morgan survey sea wrack on a Puget Sound beach. Credit: Megan Dethier
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.
“Ultimately we need to bring this research around to what people care about,” says Dethier. “They usually don’t care, or they feel negatively, about stinking seaweed.” The fish findings speak to more common concerns. Heerhartz’s snorkel surveys didn’t find notable differences in the numbers of young salmon swimming along armored and unarmored beaches — only in the ways they swam. The little coho, chums and Chinooks tended to power past the bulkheads but linger and meander along unarmored beaches, indicating that they were feeding and hence that those beaches had more little critters to feed on.
An amphipod. Aka lunch for a young salmon. UW
A third paper, which the researchers are still working on, may provide some illumination on that score. It will analyze the populations of insects and amphipods on the two types of beaches.
Amidst all the challenges of documenting so many phenomena at so many sites, Dethier and Heerhartz faced a special hurdle: getting landowners’ permission to study their beaches. “People with armoring are very beleaguered,” she says. “I was regarded as the enemy. I can’t blame them. If I had a million-dollar house and people kept telling me I should take out my armoring, I would be wary.”
Nevertheless, she recalls “ the exceptions—people who came down and brought us coffee and cookies when we were working in front of their seawalls. Other people threatened to call the sheriff.”
What impressed Dethier most, however, was the number of beach walkers who stopped to ask about the processes she was studying — and how much they had to share on the subject. “It was neat to hear them tell stories about how things were 20 years ago —‘The beach used to come down to here…’ Somebody should be collecting this sort of mental baseline. It would be very appropriate for studying large areas of Puget Sound. It’s anecdotal, but if you get enough anecdotal evidence it can be useful.”
Indeed, it might provide the sort of history gained from accumulated studies elsewhere. “But it needs a sociologist,” Dethier sighs. “That’s not me.”
Photo of Sarah Hearhartz by Jesse Colangelo-Lillis.
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