On Nature column: How rising temperatures threaten coral reefs

For The Herald Bulletin

Sheryl Myers

The Florida Keys Reef Tract is the largest barrier reef in the United States and the third largest in the world. It is home to many species of both stony and soft coral, sponges, lobster, grouper, urchins, sharks, whales, dolphins, conch (pronounced conk), sea turtles, squid, octopuses, and colorful tropical fish.

The Florida Keys are a string of limestone islands that were once a part of extensive coral reefs and sandbars that flourished 125,000 years ago, before successive ice ages caused sea levels to drop.

The Keys (also spelled Cays) together form a barrier reef that runs parallel to land with a lagoon between the reef and the shoreline. The reefs buffer the shore from storms, help prevent beach erosion, and are home to a rich diversity of marine life unparalleled in complexity by anything on land except the tropical rain forest.

Boat operators need depth maps to navigate areas with coral reefs because the calcium carbonate skeletons of unseen coral can rip gaping holes in the bottom of a boat.

Coral reefs are majestic jewels of biodiversity that support an estimated 25% of all known marine species. They are found almost exclusively in the tropical latitudes, a belt running from 23½ degrees north to 23½ degrees south.

Coral is made up of many hundreds or thousands of individuals living side by side in a colony, each cemented to a skeletal structure of calcium carbonate (limestone). They all live on the skeletons of previous residents.

Like their close relatives the jellyfish and sea anemones, coral are mostly clear and colorless yet appear to be yellowish-brownish-green. Why? Living within their bodies are microscopic algae-like organisms called zooxanthellae.

These guest algae make enough food for themselves and their coral host. They also give coral their color. However, if the water temperature gets much higher than 80 degrees Fahrenheit, zooxanthellae produce toxic molecules that accumulate inside the coral’s tissue and the coral expels them. The coral returns to its colorless state, a condition called bleaching. This is bad news for coral because their guest algae produce over three-quarters of the food that they consume. Prolonged water-warming events can kill entire coral reefs. We are experiencing a bleaching event that started in July of this year.

Marinelab is a marine science educational facility on Key Largo. On Aug. 4, I spoke with Rachel Carrier at Marinelab about the current condition of the reefs.

She said, “A good portion of our reefs are bleached; some have just died. The reefs in deeper water are healthier.”

She reportedalso that some small reefs are completely dead, but they might also be affected by a disease called stony coral tissue loss that was first identified in 2014 and has been spreading rapidly.

All things considered, the coral reefs of the Florida Keys are in trouble.

Sheryl Myers taught biology and environmental science for 34 years and has worked as a naturalist for area parks. She is a founding director of Heart of the River Coalition.

Sheryl Myers

Meet your Best of Madison County 2023.

Graduations, games or events, order prints of your favorites photos from The Herald Bulletin.