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Disease Outbreak Affects the Brain Coral Colpophyllia natans on Bird Key Reef in the Dry Tortugas.

Something is killing the brain coral Colpophyllia natans on Bird Key Reef in the Dry Tortugas. The apparent cause is a disease outbreak. Colonies hundreds of years old and 6 feet across have died since last year.

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by M. Lybolt¹, J. Wheaton¹, W. Jaap¹, and K. Hackett¹.

¹Florida Fish and Wildlife Conservation Commission-Fish and Wildlife Research Institute

Something is killing the brain coral Colpophyllia natans on Bird Key Reef in the Dry Tortugas. The apparent cause is an unidentified disease. Several very old (100 years +) colonies have died since last year.

Credit: Florida Fish and Wildlife Conservation Commission (FWC)

Colpophyllia natans (Houttuyn, 1772) Common Name: Boulder Brain Coral or Giant Brain Coral

Credit: Florida Fish and Wildlife Conservation Commission (FWC)

Colpophyllia natans, colonies are usually found as large round domes or large encrusting plates. The colony surface is covered with a convoluted system of ridges and valleys, as seen in other species of brain coral. Colpophyllia natans has a distinct groove that runs along the ridge tops. Typically the ridges are brown and the valleys green, tan, or whitish. The colonies range in size from 1.5 to 7 feet and are found at depths of 2 to 175 feet. Colpophyllia species can be found throughout the Caribbean, the Bahamas, and south Florida. According to Keith Hackett, data manager for FMRI’s Coral Reef Monitoring Project (CRMP), Colpophyllia natans, one of the top five coral species in the Florida Keys in terms of percent cover, is present at 71 of the 160 CRMP stations.

Credit: Florida Fish and Wildlife Conservation Commission (FWC)

Bird Key reef runs along the southeastern margin of the islands around Fort Jefferson in the Dry Tortugas. The reef starts at the reef crest at a depth of about 1 meter and extends to a depth of 28 m (90 feet). Like many other reefs in the Keys, Bird Key reef has been the site of long-term studies. FWRI research at Bird Key began in the mid-1970s with monitoring of a 13-square-meter (13 m²) area. This monitoring site is still visited for sampling about once every three years. Also in the mid-1970s, FWRI collaborated on the establishment of a kilometer-long cross-reef transect line named TRACTS. The TRACTS line served as a baseline for cross-reef studies and a reference point for other Bird Key studies. In 1999, FWRI’s CRMP established another set of coral-monitoring sites covering 160 m² and nearly overlapping the older project locations. The CRMP monitoring sites are visited once each year.

Credit: Florida Fish and Wildlife Conservation Commission (FWC)

Annual monitoring for 2002 was conducted by the CRMP in the second week of May. From their initial observations, the research team estimated that roughly 50% of the Colpophyllia natans colonies on Bird Key reef had died since the monitoring visit in 2001. Active disease was apparent on several of the remaining live colonies. Close-up photographs were taken of the disease margin (see above), and mucous samples were collected for DNA analysis by Dr. Dale Griffin at the United States Geological Survey, Center of Coastal & Regional Marine Studies in St. Petersburg.

The data collected in May were analyzed in the lab, and the results are shown on the graph above. Two facts are obvious. First, from 1999 through 2001 the percent cover of Colpophyllia natans on Bird Key reef was relatively stable. Second, from 2001 to 2002, percent cover at all four stations decreased, with three of the four showing a decline of more than 50%. In the span of only one year, the average percent cover of Colpophyllia natans at Bird Key declined by 70%!

Some of the underwater video taken in May was converted into mosaics using RavenView software. These mosaics depict changes at the site from 1999 through 2002, showing clearly that large colonies of Colpophyllia natans alive in June 2001 were dead by May 2002. 

Credit: Florida Fish and Wildlife Conservation Commission (FWC)

Image of two neighbor colonies, one alive and healthy, one completely dead.

Prior to July 1, 2004, the Fish and Wildlife Research Institute (FWRI) was known as the Florida Marine Research Institute.