Coral Reefs

queen angelfish
Queen angelfish (NPS image)
"No sea-lover could look unmoved on the blue rollers of the Gulf Stream and the crystal-clear waters of the reef, of every delicate shade of blue and green, and tinged with every color of the spectrum . . . a sort of liquid light, rather than water, so limpid and brilliant is it." - Commodore Ralph Munroe in 1877

Park visitors may experience a kaleidoscope of colors and frenetic movements. Blue neon gobies and yellow striped porkfish punctuate a background of golden-brown elkhorn corals and swaying purple sea fans. A loggerhead sea turtle takes a breath at the surface as a young nurse shark settles to the bottom.
feeding polyps
Corals extend tentacles to trap food particles. (NPS image by A. Bourque)
Tiny coral animals, called polyps, obtain calcium from seawater and use it to build cup-like external skeletons around themselves. Generations of polyps create fantastic colonies that appear in the shapes of flowers, mountains or elk antlers. Colonies of different coral species create the living fortresses we call reefs.

Other reef dwellers include sea whips, sea fans and other soft corals that sway in the current and give the whole reef the appearance of movement. Bright sponges filter small plants and animals from the water. Christmas tree worms burrow into stony coral skeletons, adding tufts of red, orange and purple to the grooved surfaces of brain corals. Algae and other plants are important food sources for fish, shrimp, crabs and a myriad of other animals.
nurse shark
Nurse shark glides through a coral reef. (NPS image by A. Bourque)
Like a bustling city, the reef is active day and night. Polyps on the soft corals withdraw as hard coral polyps emerge for a night of feeding. Parrotfish and wrasses wrap up in mucous sleeping bags, as octopi and squirrelfish become active. This "shift change" ensures that the reef's plentiful food supply is utilized around the clock.
queen angelfish
Queen angelfish (NPS image by A. Bourque).

For many, it is the fish that give reefs their magical qualities. The park is home to an incredible array of over 500 species of reef fish. The diversity of colors, shapes, sizes and behaviors is amazing. Inch long damselfish nip at diver facemasks, attempting to chase them away from carefully tended algae gardens. A green moray hovers nearby, mouth agape, at the entrance to its lair. A variety of fish wait at a "cleaning station" where tiny gobies scour their bodies for parasites. A stoplight parrotfish chomps on coral, devouring algae, polyps and stone in bites. A 500 pound goliath grouper peers out from under a ledge. A pair of spotfin butterfly fish float effortlessly through the water.

Reef organisms
There are many unique sponges on coral reefs (NPS image by A. Bourque).

Coral reefs are among the most biologically diverse ecosystems on earth. Every crack and crevice seems to be occupied. Knowledge of reefs is constantly growing. This knowledge will be increasingly valuable as reefs around the world experience problems from pollution, overfishing, boat groundings, climate change, marine debris and disease.

The reefs of South Florida are accessible to millions of people who visit and live in the greater Miami area. For this reason, the reefs are also very vulnerable. When diving, snorkeling or boating, please remember the following tips:

  • Tiny coral polyps are fragile and easily damaged by the slightest touch.
  • Be aware of where your feet are placed and be careful not to cause damage with fins.
  • Use proper nautical charts to avoid running aground.
  • Use mooring buoys where available and ensure that anchors are not set in corals.

Simple things you can do to make a difference for the health of the reefs include avoiding anchoring on hardbottom, never tossing debris overboard and retrieving fishing gear and line that gets away from you.

Image shows a cluster of white, knobby corals that are bleached nearly white
Coral bleaching on a reef in Biscayne National Park

NPS photo by Peter Wintersteen

Corals often respond to stress, such as increased water temperatures, by expelling the colorful algae called zooxanthellae that live within their clear tissues. When this happens, the coral appears 'bleached' as its white skeleton is visible through its tissues. As zooxanthellae provide most of the coral polyp's food, prolonged bleaching can cause the polyp to starve. Additionally, bleaching weakens corals making them more susceptible to disease and injury. If stressors subside in a timely fashion, corals can take in new zooxanthellae and survive bleaching events.

Coral bleaching is a major contributor to the decline of reefs worldwide. With the loss of coral, comes the loss of habitat for a tremendous variety of marine life. Healthy reefs provide shoreline protection for coastal communities by absorbing wave energy and reducing flood risk. Coral decline through bleaching and other stressors reduces that protection.


The Effects of Coral Bleaching

Well-named staghorn coral grows in a dense tangle. Bright orange tines of coral stick out in every direction. Well-named staghorn coral grows in a dense tangle. Bright orange tines of coral stick out in every direction.

Left image
Credit: NPS Photo by Morgan Wagner

Right image
Credit: NPS Photo by Vanessa McDonough

The two images seen here were taken at the same thicket of staghorn coral on the coral reef. The bright orange coral colonies are vibrant, and healthy; white tips indicated new growth. Bright white coral indicates bleaching; its symbiotic algae has been expelled and the coral may soon die.


The Effects of Coral Bleaching, Continued

Staghorn coral colonies that have bleached. The white mass of spikey coral colonies resemble piles of bones strewn across the seafloor. Staghorn coral colonies that have bleached. The white mass of spikey coral colonies resemble piles of bones strewn across the seafloor.

Left image
Credit: NPS Photo by Vanessa McDonough

Right image
Credit: NPS Photo by Vanessa McDonough

Due to an extended period of extremely warm water during the summer months of 2023, the thicket of staghorn coral bleached, but was unable to recover. After the coral polyps died, algae grew over the coral skeletons left behind. Although similar in color, the algae is not to be mistaken with the once-healthy coral colonies. This event happened throughout the park, to many species of coral, and throughout the Florida Reef Tract.


Last updated: December 10, 2023

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