Sea urchin die-off threatens reefs from Florida to Caribbean. Scientists hope to revive them

MIAMI — These days, long-spined sea urchins are known as the gardeners of the sea. They tend the algae on the coral reefs they call home, making sure it never overwhelms their hosts. Spotting one on the Florida reef tract is a good sign that nearby corals are doing OK. Decades ago, their reputation was a little different. They were viewed as damaging nuisances — to divers and to reefs. The first time marine scientist Don Levitan saw the reefs near the U.S. Virgin Islands, they were blanketed in black — the coral covered by thousands of urchins spiked with sharp, poisonous spines. “It was so de...