NSU rescuing heat-damaged corals in S. Fla

South Florida’s coral reefs are really struggling.

We’ve all seen the stories about how coral reefs, thanks to extremely high water temperatures, are experiencing a bleaching event like never before.

Less talked about is how these high temps have accelerated a deadly disease that has threatened corals for years.

Stony coral tissue loss disease, called SCTLD, causes lesions that move quickly across affected coral colonies, often killing them within weeks.

The number of diseased corals has skyrocketed due to recent extreme temps. Since May, researchers treated 331 corals belonging to 12 species in Broward and Miami-Dade counties. In just three months this was more than the total yearly treatments in any prior year.

“We had the most diseased large corals last summer than any previous year, and this year looks to be much worse,” said Brian Walker, who holds a doctorate and is research program director of Nova Southeastern University’s GIS & Spatial Ecology Laboratory in the Halmos College of Arts and Sciences.

This summer Walker’s team treated more lesions than any previous June. The number of treatments and amount of corals treated in July was the third highest since monitoring began. And August was the highest yet.

The recent heat wave has increased local Florida water temperatures, causing a massive bleaching event throughout the Florida Keys.

In extremely warm waters, corals lose their symbiotic algae that provide them with essential nutrition, a condition that causes death in prolonged heat. Even worse, SCTLD is thought to be related to the symbiotic algae and its spread is exacerbated by high temperatures.

Walker’s research team recently found that four years of temperature, rainfall, and inlet flow data explained 66 percent of the variation in the number of corals with lesions. Similar models of reef water quality sites found that inlet flow, rainfall and wind predictors explained 79 percent of the variation in orthophosphates and 55 percent of nitrates.

This suggests that SCTLD is exacerbated seasonally by excessive nutrients during increased rainfall and inlet flow rates during high temperature periods.

So far, 2023 has proven to be exceptional by both having an early rainy season and an extreme unprecedented heatwave.

According to the South Florida Water Management District, rainfall in Broward was over 300 percent above average in April, followed by reports from the National Oceanographic and Atmospheric Administration showing the highest ocean temperatures ever recorded in the Florida Keys.

“We typically see increases in coral disease every year that coincide with the onset of the rainy, summer season between May and October where the number of lesions and diseased corals increases, but never like this year,” said Walker. “This year’s combination of high rainfall and extreme temperatures is proving to be disastrous for corals in South Florida.”

Since 2018 the GIS and Spatial Ecology Lab monitors and treats disease each month on over 100 of the largest, oldest, most resilient colonies in southeast Florida.

Saving these reef-building corals is a priority because they have a higher reproductive potential, increasing the natural ability to replenish the reef that provides reef structure and habitats for many organisms.

An antibiotic paste called CoralCure is helping to smother disease lesions, and in some cases create a disease-break. Researchers cut a small trench about 5 centimeters from the visibly diseased margin using an underwater grinder to isolate the visually diseased portion from the rest of the colony.

Funding for the project is provided by Florida’s Department of Environmental Protection, the National Fish and Wildlife Foundation and US Environmental Protection Agency.

Researchers have collected pieces of corals, broken off by activities like anchoring and storm damage, to use in restoring the large corals they came from. Fragments were brought to NSU’s onshore coral nursery, where they remain until they can be “outplanted’ back on the reef. That restoration is now on hold as the team ramps up efforts to find and treat as many diseased corals as possible.

“It’s really a two-pronged effort to help,” Walker said. “First, when possible, fragments are saved and cared for, with the goal of returning them to the reef.

“Second, we’re working tirelessly to treat diseased corals to help stop the spread of the disease and provide help so the reef can recover.”

South Florida residents can play a part in saving corals too.

Divers who come across diseased coral, can go online and report the location to the Southeast Florida Action Network (SEAFAN) or call the SEAFAN hotline at 866-770-SEFL (7335).

Story courtesy of Nova Southeastern University.