By Scott Atwell
At 18 feet above sea level, Solares Hill is the highest point of land in Key West, yet the lofty elevation would have been no match for waves produced offshore by Hurricane Helene last September, had the wall of water reached shore.
It didn’t, thanks to a coral reef structure seven miles away at Eastern Dry Rocks, where more than 90% of wave energy was dissipated. Helene was one of three storms that affected the Florida Keys in consecutive months last fall, each of which was monitored by sensors at Eastern Dry Rocks, one of seven reefs being restored as part of NOAA’s Mission: Iconic Reefs.
“Without the barrier reef system, much of the Keys would be exposed to the full brunt of ocean swell,” says Jim Hench, an associate professor of oceanography at Duke University who led the monitoring program. “But the reefs, through their complex structure and frictional properties, interact with the waves, convert wave energy into turbulent energy, and then heat. That’s the dissipation mechanism.”
As Hurricane Helene passed the Keys on Sept. 26, 2024, as a Category 1 storm, a buoy at Satan Shoal measured 19-foot waves, with one peak reaching nearly 30 feet. Eight miles away, an array of 26 sensors at Eastern Dry Rocks recorded wave energy over a one-kilometer area across the reef, from front to back.
“The pressure difference is measured by how much water is over the sensor,” said Andy Bruckner, chief scientist at Florida Keys National Marine Sanctuary. “The wave rises as it comes through, creating more downward pressure. As it passes, there’s less.”
In 2022, Hurricane Ian produced 26-foot waves at Satan Shoal, and sensors at Eastern Dry Rocks recorded more than 90% mitigation. The data will serve as a baseline to calculate how reefs can dissipate wave energy as Mission: Iconic Reefs restores coral over 20 years.
More than 11,000 corals were outplanted at Eastern Dry Rocks over the first five years of the program, but the summer heat wave of 2023 slowed progress. The current outplanting season is scheduled to include thousands of corals that have shown heat tolerance.
“Restoration moving forward will be more targeted,” said Katey Lesneski, research and monitoring coordinator for Mission: Iconic Reefs. “We will be focused on areas where corals have survived past heat stress, and with the goal of expanding those resilient populations. Practitioners will also be incorporating more resilient species and genotypes at other sites. Coral reefs don’t recover overnight — but informed, adaptive restoration gives them a fighting chance for the future.”
The National Marine Sanctuary Foundation funded the start of the wave monitoring program, but the grant expired. The sanctuary will now partner with the College of the Florida Keys, which is providing sensors that measure wave direction, as well as student divers to maintain the system.
Mission: Iconic Reefs would like to expand the monitoring program to other reefs, adding control sites that are not being restored, as well as inshore stations. “The longer-term goal is to get sensors set up from the shore to the reef,” said Bruckner. “Right now, we’re only looking at that first buffer, and waves may build up again because the wind is still there. We don’t know how that changes all the way to the shoreline.”
