MIAMI — If sea rise weren’t scary enough, scientists have now found another phenomenon threatening the Florida Keys and other coasts protected by reefs: a vanishing ocean floor.

In a study published Thursday in the journal Biogeosciences, a team from the U.S. Geological Survey documented a dramatic erosion of the sea floor around coral reefs, ranging from a few inches to nearly 3 feet since the 1930s. Combined with sea rise, the disappearing bottom means the hazards facing coasts – storm surge from hurricanes and even erosion from everyday waves – will likely be worse than now projected, especially for the low-lying Keys.

“We worked very hard to try to prove ourselves wrong because the change was so striking,” said lead author Kimberly Yates. “And we just could not do that.”

The study, which focused on the Upper and Lower Keys, the Virgin Islands and Maui, found water now at depths that had not been predicted to occur for another eight decades. That’s because with sea floor loss factored in, sea rise occurred at a far faster rate than previously thought. Other reefs are likely experiencing the same losses, Yates said, meaning many more coastal communities armored by reefs may face higher threats.

The study focused on the changes – comparing historic water measurements to modern ones – and did not address causes or re-calculate future sea rise.