How anti-erosion measures hurt fish—and living shorelines may help.
by Amorina Kingdon - Hakai Magazine
Photo by Jimmy Jacobs
The land beneath Chesapeake Bay, the largest estuary in the United States, is sinking. Couple that with climate change, and the sea level is rising twice as fast as the global average, chewing away at shorelines and drowning islands. Private landowners, who occupy about 85 percent of the shoreline, have responded with walls, rocks, and barriers, which have helped slow the losses. But evidence is growing that this coastal hardening may be insufficient at holding back future seas, and is doing serious damage to more than a dozen fish and crustacean species. Now, planners and landowners are hoping engineered living shorelines can solve both problems at once.
A hardened shore makes life more difficult for trout, perch, crab, and other species that need a natural shoreline to thrive, says Matthew Kornis, who recently published a paper evaluating the effect of shoreline hardening on these species.
Kornis, a fish biologist with the US Fish and Wildlife Service, studied hundreds of sites in and around Chesapeake Bay, from natural beaches and marshlands, to shores lined with riprap (cages of loose rock) and bulkheads (walls, often wooden). The harder the shoreline, he found, the harder hit the species. This was true even for riprap, which is often considered more environmentally friendly than sheer walls.
Kornis says natural shorelines offer things hardened shorelines don't: juvenile fish live in the nooks and crannies of rocky shorelines, for instance, and these environments serve as nurseries. Fish also feed within beds of seaweed and seagrass. Hardening decimates these complex habitats, leaving nothing to eat and nowhere to hide.
Hardening isn't unique to Chesapeake Bay. Estimates suggest that about 14 percent of the United States' coast had been hardened, and the shorelines of Europe and China are also heavily armored. While the motivations for reinforcement vary (development, industry, sea level rise), most Chesapeake Bay residents are trying to protect their property from rampant erosion. Sea level rise is a relatively new problem for many coasts, but land subsidence means it's been the norm in the Chesapeake for a long time.
"Erosion has been happening for centuries," says Zoe Johnson, climate change coordinator with the US National Oceanic and Atmospheric Administration in Chesapeake Bay. Tide gauge data shows the water rose nearly a third of a meter in the past century. Similarly, the sea moved inland by roughly half a meter a year on average. But these rates are accelerating as climate change adds a rising sea to sinking land. "The influence of global factors will outpace the land subsidence," she says.
In the early 2000s, Maryland convened a climate change task force, including Johnson, to study how to better adapt to these future seas. They identified one promising method that seemed to stand up to the sea: living shorelines.