Rage against the dying of the reefs.

• Author: Helvarg, David

I first saw coral reefs and the abundance of life they generate as a teenager on a trip to Key West in 1967. Tropical reefs cover less than 1 percent of the ocean, but are home and nursery to 25 percent of all marine species; billions of fish, mollusks, and other creatures rely on reefs for food and shelter. Their vast beauty is generated by tiny living coral polyps, whose calcium carbonate skeletons build up bedrock structures over millennia.

Today, reefs generate huge tourism revenues for warm water nations and regions fringed by them. Their unique productivity also assures food security for hundreds of millions of people. Plus they act as storm barriers providing protection to coastal populations from South Florida to Indonesia at a time of rising sea levels and intensified hurricanes.

The Great Barrier Reef is the largest living thing visible from space. Stretching 1,400 miles along Australia's northeast coast, it covers only one-tenth of 1 percent of the world's ocean surface yet supports 8 percent of the worlds known fish species, about 1,500, plus more than 500 species of living coral: hard, soft, branching, and leafy.

I first dove Australia's Great Barrier Reef in 1990, having dreamed about it since childhood. It was all I'd hoped for: warm, gin-clear waters vibrant with life, including giant potato cod (grouper), blue-green Napoleon wrasse, sharks, and multihued parrotfish crunching coral and excreting sand. There were canyons and bommies and walls with branching elkhorn, staghorn, plate, and fan corals. There were coral gardens in brown, green, red, pink, and purple, crevices full of moray eels and queen angelfish, and shelves of multiquill geisha-like lionfish along with red and blue spotted coral trout amidst a rainbow confetti of smaller fish, including clowns, damsels, sweetlips, chromis, and Moorish idols. The boulder-sized giant clams with their beautiful soft mantels of purple, green, and red algae-covered mollusk skin that opened like fat lips to the sea seemed to have calmed down considerably since my early TV viewing, when they trapped Sea Hunt's Lloyd Bridges by the leg and tried to drown him.

I shared that first boat trip on the Great Barrier Reef with my late love and dive buddy Nancy Ledansky. She died of breast cancer at the age of forty-two in 2002. More than a fifth of the Great Barrier Reef that is 6,000 to 8,000 years old died in 2016. Not coincidentally, that was the planet's hottest year since modern recordkeeping began in the nineteenth century.

Sixty-seven percent of the reef segment north of Port Douglas is now dead rock. This latest coral die-off is the result of the third and most persistent global bleaching event since 1998; all are linked to fossil-fuel-fired climate disruption.

A new study that recently made the cover of the science journal Nature documents vast coral death along a 500-mile section of the reef. Where we took our dives, some patches are more than 80 percent gone. Other parts of the northern reef have seen less extreme die-offs, averaging 17 to 35...