fish swim in a coral fish
Coral reefs provide habitat for fish and many other species of marine life.

NPS photo by John Dengler

The coral reefs of Dry Tortugas National Park harbor a rich and colorful variety of marine life such as fish, lobsters, sponges, sea stars, and anemones. Clear waters with excellent visibility attract snorkelers and SCUBA divers to the park, which offers some of the best underwater viewing opportunities in the United States.

The park is home to about 30 species of coral. Corals are marine organisms that typically live in colonies consisting of many individual soft-bodied organisms called polyps, each only a few millimeters in diameter. After a polyp attaches itself to a hard substrate on the sea floor, it divides itself into thousands of clones. The polyps cement themselves to each other by secreting a skeleton of calcium carbonate, thereby creating a colony that acts as a single organism. Over the course of hundreds to thousands of years, the colonies join together to form reefs.

white splotches on a diseased coral
Stony Coral Tissue Loss Disease lesions were found on a Dichocenia stokeseii (Elliptical Star Coral) colony in May 2021. Park staff immediately applied an antibiotic paste, the best treatment available for the disease, around the diseased part of the coral.

NPS photo by Rachel Johns

By themselves, coral polyps are translucent and colorless. But they host billions of colorful zooxanthellae, a type of algae that gives corals their vivid colors. These zooxanthellae also provide corals additional nutrients. Physical stress, such as temperature change or pollution, causes the zooxanthellae to die and the corals to lose their color, thereby exposing the white of the coral’s calcium carbonate skeleton. Dying zooxanthellae result in coral bleaching, a process that can kill entire colonies of coral if environmental conditions do not improve. Although corals grow in tropical waters throughout the world, the reefs in southern Florida grow at the northernmost extent of their limit. Like other corals, they are susceptible to impacts from other adverse conditions, such high sea water temperatures and pollution.

In May 2021,
Stony Coral Tissue Loss Disease, an infectious, water-borne disease that impacts hard coral species and damages entire reefs, was identified on corals in the park. The disease now spans all of Florida's Coral Reef and the Caribbean.

scientist underwater taking notes about coral
Park biologists routinely monitor the health and size of coral colonies and correlate the findings with constantly changing environmental conditions.

NPS photo (Submerged Resource Center)

Dry Tortugas National Park biologists monitor the health and size of coral colonies and correlate the data with environmental conditions, which are constantly changing. The park is home to nine species of threatened coral:

  • Elkhorn coral (Acropora palmata) is structurally complex with many large branches that that grow in a structure reminiscent of elk antlers. The branches range in color from brown to yellow brown and create habitat for many reef-dwelling species of marine wildlife.
  • Staghorn coral (Acropora cervicornis) is the fastest growing species of all corals growing in western Atlantic waters. Both species of coral are subject to disease outbreaks, hurricanes, bleaching, algae overgrowth, human impacts, sedimentation, and variations in temperature and salinity.
  • Elkhorn coral (Acropora palmata)
  • Staghorn coral (Acropora cervicornis)
  • Pillar coral (Dendrogyra cylindrus)
  • Rough cactus coral (Mycetophyllia ferox)
  • Lobed star coral (Orbicella annularis)
  • Mountainous star coral (Orbicella faveolata)
  • Boulder star coral (Orbicella franksi)

Last updated: April 29, 2024

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