Using underwater medicine to prevent disease-related mortality on corals in Dry Tortugas National Park

By: Dr. Karen Neely, Nova Southeastern University

Takeaway: As corals in Dry Tortugas National Park were being ravaged by an unprecedented disease, the NOAA-NFWF Coral Emergency Response Fund was used to quickly and efficiently implement intervention cruises that treated over 12,500 actively diseased corals, potentially saving up to 331,000 coral outplants.

Stony coral tissue loss disease (SCTLD) has been a catastrophic source of coral mortality in Florida and the Caribbean. First appearing off Miami in 2014, it has since spread through Florida’s Coral Reef and to most other regions of the Caribbean. It appeared in Dry Tortugas National Park, at the far western end of Florida’s Coral Reef, in late spring of 2021. A rapid collaborative response was mounted by nearby research institutions and Dry Tortugas park staff. Using liveaboard research vessels, a total of three intervention-specific missions targeted three high-priority reef areas within the Park which were experiencing extremely high levels of SCTLD infection and mortality. Divers spent over 546 hours underwater, covering a reef area equivalent to 91 soccer fields. Each buddy team conducted four dives a day, swimming search patterns up and down the reef line looking for any diseased corals and applying treatments.

A series of maps with increasingly zoomed in focus to coral reefs in the Dry Tortugas.
Top: Location of Dry Tortugas National Park noted by the yellow star (left) and location of coral reefs within park boundaries (right). Targeted reefs outlined in boxes. Bottom: Reefs targeted by intervention cruises. Colored lines on maps represent daily tracks of intervention dives.

Disease-affected corals were treated with a specially formulated underwater medicine consisting of amoxicillin mixed into a paste designed to release the medicine directly into coral tissues over three days. The paste is applied directly to disease lesions, and is around 90% effective in stopping lesion progression. A total of 12,521 corals, representing 28 different coral species, were treated. The coral tissue saved from immediate loss to SCTLD is estimated to be equivalent to over 331,000 coral outplants.

A scene of multi-colored corals, most with white areas of mortality, and white coral skeletons  in the top left. A diver hovers over a large coral, applying a white line from a tube onto the coral on the right. Several tan coral heads with living tissue, dead tissue, and a white line outlining the live tissue on the bottom left.
Dry Tortugas reef with high SCTLD prevalence before (top) and after treatments (bottom). Diver treating a coral with active SCTLD lesions (right).

These efforts represent an extremely efficient method of avoiding rapid loss of coral cover and species diversity on reefs. On average, a diver could treat a coral every 1.5–2 minutes. Though reefs in Dry Tortugas and throughout the Caribbean represent too vast an area for treatment to occur everywhere, the priority reefs addressed through these efforts may help provide the reproductive potential and ecosystem services required to help replenish others in the region.

Treatment of diseased corals is still occurring and will continue into the future throughout Florida and many regions of the Caribbean. Within Florida, National Park Service staff continue to work in Dry Tortugas and Biscayne National Parks, and Nova Southeastern University staff continue intervention efforts within the Florida Keys National Marine Sanctuary and the southeast Florida region. In total, over 24,000 corals have been treated for SCTLD in Florida. Unfortunately, the capacity of this small number of divers and limited funding has meant that many millions of diseased corals could not be treated, and perished. SCTLD continues to be the primary source of mortality to regional reefs, and ongoing efforts are essential to preserve remaining corals.

Side-by-side photos showing a close up of numerous corals covering a substrate. On the left, white arrows point to areas of recent mortality that are a lighter color than the adjacent live tissue. On the right, the corals have been treated, as shown by white paste around the lighter color spots.
Dry Tortugas reef showing location of active SCTLD lesions on corals before treatment (left) and after the application of a topical medical paste (right).

This project was led by Nova Southeastern University coral biologists, with assistance from science divers from Harbor Branch Oceanographic Institute and the University of the Virgin Islands, and in collaboration with the National Park Service. The work was funded by the Coral Emergency Response Fund, a partnership between National Fish and Wildlife Foundation and NOAA’s Coral Reef Conservation Program.

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