Rapture of the Deep

The coral-reef formations are eerily vivid through transparent panels in the glass-bottom boat. Rainbow parrotfish—their brilliant markings doing justice to their name—glide above the reef, flanked by black-and-white-striped sergeant majors, bluehead wrasses, black groupers, yellowtail damselfish. A spotted eagle ray sweeps into view as translucent moon jellyfish waft by.

A coral reef is a complex world unto itself, an elaborate ecosystem whose denizens range from microscopic zooxanthellae (organisms that give coral its color) to 3,000-pound Atlantic manta rays. Parrotfish ingest coral and rock as they graze on algae, and excrete the sediment as fine sand. Shrimp scavenge decayed food morsels from the teeth of moray eels. Blowfish consume crustaceans. The millions of tiny polyps that compose the coral ensnare and devour tiny organisms.

At John Pennekamp Coral Reef State Park in Key Largo, the first undersea preserve in the country and the most-visited state park in Florida, more than a million people each year discover an underwater reality light-years removed from the endless sprawl of T-shirt and sandal shops, restaurants and discount stores crowding the route south from Miami into the Upper Keys.

Pennekamp was named after a 1950s Miami newspaperman who, along with University of Miami marine biologist Gil Voss, fought to set aside the area as a park. Along with the adjacent Florida Keys National Marine Sanctuary, the preserve covers approximately 3,066 nautical square miles and protects the largest living coral reef system in the continental United States. Some 25 miles long, the reef extends east into the Atlantic for three miles, at which point one enters federal sanctuary waters.

Visitors can explore the reef from a glass-bottom boat, on snorkeling tours or on scuba-diving expeditions (a one-day "resort course" is available, enabling even a neophyte to take the plunge). Powerboats, canoes and kayaks also are available for rent. A water trail for paddlers winds among tangled roots of mangroves, trees that live in saltwater. The roots provide a haven for birds and a "nursery," as park biologist Chris Rader describes it, for fish as well as shrimp and other crustaceans. Fine snorkeling can be had right off the beach, and a boardwalk wends its way through the mangrove swamps.

The primary attraction, however, remains the coral reef, an organism between 5,000 and 7,000 years old. "These are probably the oldest living animals you'll ever see," says Rader. A coral, he explains, is a type of soft invertebrate called a polyp; as corals grow, they excrete a calcium-carbonate (limestone) exoskeleton, which builds up under the polyps to form the reef. This particular reef—crisscrossed by sandy channels and sea-grass beds—contains one of the most diverse populations of marine plants and animals in North America.

While the glass-bottom boat tours provide a good introduction to the reef, snorkeling or scuba diving is far more rewarding. As a myopic glasses-wearer, I was delighted to find I could rent a corrective mask for a mere $5. Half an hour later, with fins, snorkel and mask, I explored the waters above Grecian Rocks, one of the most popular snorkeling sites in the Upper Keys. As I had no "snorkel buddy," a group of Ukrainian women from New York City—convulsing with laughter as they taught me to yell help in Russian (Pomogitiye!)—invited me on their outing. My sharp-eyed companions pointed out barracuda and a nurse shark, lying quietly in the shallows.

Outdoors enthusiasts practice the adage "Take only pictures; leave only footprints." The staff and volunteers at Pennekamp amend that admonition: "Take only pictures; leave only bubbles."