Flower Garden Banks National Marine Sanctuary: Surveys Study Coral Bleaching

A Stetson Bank resident hawksbill sea turtle. Hawksbill eat sponges, and Stetson Bank is loaded with them! (Photo: Joyce and Frank Burek)

Widespread Coral Bleaching First Observed in Mid-October 2005

In mid-October 2005 researchers surveyed coral colonies at the East and West Flower Garden Banks National Marine Sanctuary in the Northwestern Gulf of Mexico. The cruise took place after Hurricane Rita swept through the area in September 2005. In addition to the impacts from the Hurricane, significant coral bleaching was documented. During the cruise, observations indicated that between 35 and 40 percent of the coral colonies were bleached to some extent, either partially or fully. Coral bleaching is the whitening of coral colonies that results when the original host coral organism releases the symbiotic zooxanthellae (single-celled algae) due to stress. If the stress-causing bleaching event is not too severe, the affected corals usually regain their symbiotic zooxanthellae within a few months; however, if the zooxanthellae loss is prolonged, the coral host can eventually die.

Little Recovery Observed in Late-October 2005

The painted elysia - one of three nudibranchs photographed during the May cruise. (Photo: Joyce and Frank Burek)

In Early-March 2006 there was some Improvement, but "White Plague" Becomes a Concern

Scientists again returned to the East and West Flower Garden Banks NMS during the first week of March 2006 to observe the status of the coral bleaching.  Coral bleaching continued to be present, but to a lesser extent as compared to the surveys conducted in October 2005. A number of belt transects were conducted. Within these transects that were 15 meters long by 1 meter wide, every coral colony was counted and scored as to its bleaching condition (totally bleached, partially bleached, or unbleached).

One of three species of nudibranch photographed during the cruise. (Photo: Joyce and Frank Burek)

The average number of coral colonies affected by bleaching ranged from 4 percent in the West Flower Garden to 5.7 percent in the East Flower Garden. Of the species affected, only fire coral and great star coral still had colonies that were considered “totally bleached” with most species scored as “partially bleached”. Only fire coral displayed mortality related to bleaching, but over 50 percent of the surveyed colonies of that species contained areas of dead tissue.

An observation of serious concern that surfaced during the early-March 2006 cruise was an increased occurrence of coral colonies displaying symptoms consistent with that of “white plague” type of coral disease.  White plague refers to motile marine bacteria (Aurantimonas coralicida) that progressively destroy coral tissue leaving an expanded area that appears bleached. Slightly over 2 percent of the coral colonies within the transect displayed white plague symptoms as did additional colonies in the vicinity.  White plague symptoms were noted on boulder brain coral, symmetrical brain coral, lobed star coral (M. annularis), mountainous star coral, and boulder star coral. This was the first indication of the disease this year. The first widespread disease event on record at the Flower Garden Banks NMS was reported by Sanctuary staff in the winter of 2005.

May 2006 Cruise Shows Considerable Improvement

A threespot damselfish guards eggs that have been laid on a star coral. (Photo: Joyce and Frank Burek)

Researchers were back out at the Flower Garden Banks National Marine Sanctuary for the Spring Research Cruise on May 17-19, 2006, on board the Gulf Diving vessel, M/V Fling. Participants on the cruise included researchers from the University of Houston, George Mason University, Flower Garden Banks, and Florida Keys NMS. Photographers from Azure Photography also participated in the cruise.

The cruise served as an opportunity to conduct additional follow-up surveys of the widespread bleaching and coral disease outbreak that occurred as a result of Hurricane Rita.

A new record of sand dollar at the FGBNMS - Clypeaster subdepressus. (Photo: Joyce and Frank Burek)

The surveys indicate that the bleaching event has subsided with very few heads of great star coral remaining that show signs of bleaching.  Anecdotal observations indicate a loss of fire coral, which will be quantitatively documented during the upcoming long term monitoring data collection cruise scheduled for June 2006.  The “white plague” type of coral disease event reported and documented in March 2006 appears to have slowed down with very few colonies still displaying active lesions.  Again, anecdotal observations suggest some overall cover loss in locally affected areas, and this may be quantified through the annual long term monitoring effort.

An interesting observation during the cruise was the sighting of a sand dollar (Clypeaster subdepressus) at the West Flower Garden Bank – this is the first report of this species in the Sanctuary!  A corkscrew anemone (Bartholomea annulata) was also observed at the Flower Gardens for the first time.