Sea level rise driven by human-caused climate change may have wiped out an entire species in the U.S. for the first time.

Why it matters: The loss of the only known stand of Key Largo tree cactus in the U.S. shows how rising seas can alter the coastal environment.

  • It may be the first sea level rise-related loss of a species in the U.S., although globally, other species have been lost to this and other climate-related factors.
  • It could also be an indicator of extinctions to come for other plants and animals in similarly vulnerable environments.

Zoom in: Most people think “local extinctions due to climate change and sea level rise are something that will be affecting our grandchildren, but it’s happening today,” says Jennifer Possley, the director of regional conservation at Fairchild Tropical Botanic Garden in Miami.

Possley is a co-author of a study about the Key Largo tree cacti published on Tuesday.

  • Possley and her colleagues report a constellation of factors destroyed the cacti stand in the Florida Keys: rising sea levels and storm surges that bring saltwater and wash away the soil, along with destruction from animals that may also be linked to flooding.

The Key Largo tree cacti in John Pennekamp Coral Reef State Park were the only population of the species documented in North America.

  • The coastal cactus — which can stand as high as 20 feet and has hair around its top and flowers — is also found in a few places across the Caribbean, including northern Cuba and the Bahamas.
  • “It kind of looked like a disorganized pipe organ,” Possley told Axios, regarding the tallest examples of the species.

In Florida, it lived in a unique and rare habitat called a coastal rock barren — a limestone outcropping surrounded by mangroves — that is disappearing as sea levels rise in response to melting polar ice sheets and mountain glaciers.

The stand of 150 cacti was first spotted in 1992, and in 2007 researchers began to monitor the population about every year.

What they found: The Key Largo tree cactus decline began in 2015 when researchers found only 60 live individuals — a 50% drop from two years earlier.

  • They observed roughly half the stems were gnawed by animals, likely trying to tap water stored in the plant, they write in the Journal of the Botanical Research Institute of Texas.

Between the lines: It’s possible that behavior could also be driven by climate change-induced saltwater flooding that made freshwater scarce for the animals.

  • One year later, there were just 28 living plants (and not nearly as much evidence of animals eating the plants). The researchers decided to begin to take fragments of their stems to cultivate in a nursery.

The die-off accelerated in 2017 after a 5-foot storm surge of salt water from Hurricane Irma struck the region, and by 2019 the colony collapsed, the researchers report.

  • Salt tolerant plants began to encroach on the area.
  • “King tides” that are becoming more damaging as background sea levels increase, pushed tidal water to within inches of the tree cacti, prompting the researchers to plan a rescue of the six remaining cacti.
  • They were divided between two nurseries so they weren’t “putting all the eggs in one basket,” Possley says. Staff at the nurseries hand-pollinate the flowers.

Zoom out: The fate of the only known U.S. stand of this cactus illustrates the non-linear effects of sea level rise, in which plants, animals and human-built infrastructure can adapt at first to increased flooding.

  • But ultimately, adaptation can prove too costly or even impossible.

What’s next: The cultivated plants may be introduced to an artificial habitat — a clearing of land that, for now, is safe from sea-level rise.