Rise of ‘shoreline hardening’ threatens coastal ecosystems

The United States is covering its coasts in armor. “Shoreline hardening,” which refers to the process of adding structures such as seawalls or jetties, has become increasingly popular over the past century. In a new study, researchers estimate that more than 14,000 miles of US coastline have been transformed in this way — and the changes could spell trouble for ecosystems. These structures offer a less friendly environment for species, and they can increase erosion and cause habitats such as intertidal zones and wetlands to shrink.

The team consulted the US National Oceanic and Atmospheric Administration’s databases, which categorize shorelines across the country. The researchers calculated the amount of coastline with man-made structures along the Pacific, Atlantic, and Gulf of Mexico, including open shorelines that face the ocean and sheltered shorelines along bodies of water such as bays and lagoons. The team also tried to figure out which factors might drive shoreline hardening.

About 9 percent of open shorelines and 14 percent of sheltered shorelines on the Atlantic and Pacific coasts are hardened, the team reports in Frontiers in Ecology and the Environment. Along the Gulf of Mexico, 16 percent of all shorelines are armored.

The researchers tallied up a total distance of 14,193 miles of shoreline hardening, or about 14 percent of the country’s coasts. “Thus, shoreline hardening is likely a substantial yet largely understudied means by which humans modify and degrade coastal ecosystems in the US,” the authors write. Construction was linked to housing density, GDP, storm frequency, and wave height.

Most structures were built after 1900, the team says, and roughly 125 miles of shorelines have been hardened per year. Assuming that the trend continues and more people continue to move to the coasts, close to one-third of the country’s shores will be armored by 2100, the researchers predict. If we don’t change the way we’re managing our coasts, they conclude, “the US coastlines will likely lose their natural defenses.” Roberta Kwok | 6 August 2015

Source: Gittman, R.K. et al. 2015. Engineering away our natural defenses: an analysis of shoreline hardening in the US. Frontiers in Ecology and the Environment doi: 10.1890/150065.

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