Part 10 of 20
Pulley Ridge: America’s deepest light-dependent coral reef
Some 60 to 80 metres down in the Gulf of Mexico, Pulley Ridge is the deepest known coral reef that still lives on sunlight. You can’t dive it, but it may help other reefs survive.
Pulley Ridge is unlike every other reef on this list: no one can snorkel it, and almost no one has dived it. It lies between 60 and 80 metres down in the Gulf of Mexico, on a chain of barrier islands drowned by rising seas at the end of the last ice age. Yet corals there still grow using the faint sunlight that reaches the seabed, making it the deepest known light-dependent coral reef in continental US waters.
Why it’s special
Fishermen knew the area, and a research dredge brought up corals in 1950, but scientists only recognised the reef in 1999, when the US Geological Survey and the University of South Florida mapped it. Reefs like this, in the dim “twilight” zone, are called mesophotic reefs. Their corals spread out into flat plates to catch as much light as possible.
Scientists are especially interested in Pulley Ridge because it may act as a “lifeboat”. Its deeper water stays cooler and more stable than shallow reefs, and currents may carry fish and coral larvae from it to the Florida Keys, helping damaged reefs there to recover.
What lives there
- Plate-like corals adapted to low light, and abundant green algae.
- Red grouper, which spawn on the ridge, and other important fish species.
- Deep-reef specialists: fish and invertebrates found only at these depths, alongside species familiar from shallow reefs.
How scientists explore it
At 60–80 metres, Pulley Ridge is beyond the limits of recreational scuba, which normally stops at 40 metres. Scientists study it with remotely operated vehicles, submersibles and specialist technical divers breathing mixed gases. Expeditions led by US universities and NOAA have mapped the reef, tracked its fish and corals, and measured how larvae drift from it towards the Florida Keys and the Dry Tortugas. Their findings have helped make the case for protecting deep reefs as part of the wider reef system.
Why deep reefs matter
For a long time, coral reefs were thought of as shallow places. Mesophotic reefs like Pulley Ridge have changed that view. They cover large areas worldwide, many are poorly mapped, and they may be less exposed to some of the pressures that damage shallow reefs, such as storms and heat spikes near the surface. They are not a guaranteed refuge, but they show that reef ecosystems are larger and more connected than we once thought.
Protecting the reef
Pulley Ridge is designated a Habitat Area of Particular Concern, which bans damaging bottom-fishing gear across its core. Research continues with submersibles and remotely operated vehicles.
Where to see Florida’s reefs instead
You can’t visit Pulley Ridge, but the reefs it may help supply are easy to reach. Dry Tortugas National Park, 70 miles west of Key West by ferry or seaplane, has shallow coral and some of the clearest water in Florida, and the Florida Keys reefs are only a short boat ride from shore. See our guide to Florida’s coral reefs.
Book a trip
Compare snorkel trips, dive days and tours for this area on our partner GetYourGuide, with reviews from other travellers and free cancellation on many trips. For the full list, see the world’s top 20 coral reefs, or read about coral bleaching and the future of reefs.
Questions people ask
Can you dive Pulley Ridge?
No. At 60–80 metres it is far beyond recreational diving limits, and it is studied mainly with submersibles and underwater robots.
What is a mesophotic reef?
A coral reef in the “middle light” zone, roughly 30–150 metres deep, where corals still use sunlight but much less of it reaches them.
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