Pulley Ridge coral reef
Pulley Ridge is an exceptional coral reef ecosystem located approximately 150 miles west of southern Florida in the Gulf of Mexico. This reef is built atop a submerged chain of barrier islands and is recognized as one of the deepest coral reef systems in the United States, with depths ranging from 180 to 250 feet. The area is characterized by a diverse community of reef-building corals, primarily lettuce corals (Agaricia species), which thrive in the limited light conditions, receiving less than 1 percent of surface sunlight. Pulley Ridge also supports a variety of marine life, including at least 60 species of fish that encompass both shallow and deepwater species, contributing to its ecological significance.
This unique ecosystem benefits from its geological formation, which provides a sturdy substrate for corals, and its position along the Loop Current, which enhances nutrient availability. In recognition of its ecological importance, NOAA Fisheries designated Pulley Ridge as a Habitat Area of Particular Concern in 2019, aiming to protect it from certain harmful fishing practices. However, challenges such as climate change and ocean acidification pose ongoing threats to the health of this reef. Conservation efforts are underway to safeguard the biodiversity of Pulley Ridge, reflecting the need for continued awareness and action to protect such vital marine ecosystems.
Subject Terms
Pulley Ridge coral reef
- Category: Marine and Oceanic Biomes.
- Geographic Location: North America.
- Summary: An unusually deep coral reef ecosystem built atop a drowned barrier island chain, Pulley Ridge supports a mix of marine species drawn from both deepwater and shallow-reef communities.
The Pulley Ridge Coral Reef biome is a ridge of drowned barrier islands more than 60 miles (97 kilometers) long, located approximately 150 miles (241 kilometers) west of the southern coast of Florida in the Gulf of Mexico. The ridge system is important because of its abundance of reef-building corals (particularly lettuce corals of the genus Agaricia) and reef-associated fish. It is generally thought to be one of the deepest such coral reefs in the United States, with depths ranging to 180 to 250 feet (55 to 76 meters).
During past glacial periods, when the sea level was much lower, this area formed a north–south chain of barrier islands protecting the Gulf Coast of what is now Florida, from about Cape Coral to Cape Sable. This formation was not unlike the islands of the Outer Banks, which now protect the shoreline of the Carolinas. As glaciation retreated and the sea level rose, the island chain became submerged; it is now considered a drowned chain.
Coral Community
While drowned barrier island formations are not exceptionally rare, the Pulley Ridge system is somewhat unique because much of the southern region of this feature is covered with hermatypic stony corals. Hermatypic corals rely on a symbiotic relationship with photosynthetic cyanobacteria called zooxanthellae that live within the coral polyp and provide energy to the coral for growth. Thus, they are dependent on sunlight to survive.
While many slow-growing coral species, known as ahermatypic corals or octocorals, exist in deeper water, those types are not dependent on light and generally do not build reefs. Pulley Ridge, on the other hand, is the deepest known occurrence of reef-building corals in waters of the United States.
Lettuce corals (genera Agaricia and Leptoseris) are most abundant in the Pulley Ridge system, accounting for up to 60 percent of live-coral cover at some localities. Less common species include star corals (genus Montastraea) and finger corals (genera Madracis and Porites). Along with these key coral types, a variety of slow-growing octocorals are present here. The community also supports both calcareous and fleshy algae; a wide variety of green, red, and brown macroalgae species thrive here, despite receiving less than 1 percent of the sunlight available at the surface—or about 5 percent of the light observed on most shallow-water coral-reef systems. Sponges, too, have found a niche here to grow in substantial numbers.
Marine Life
Pulley Ridge is home to a wide array of fish, at least 60 species in all, with a mix of typical shallow-water reef fish and some deepwater species sharing this ecosystem. Among those more typically seen in shallower waters but represented here are bluehead, bicolor damselfish, rock beauty, coney, French angelfish, and hogfish. Deepwater denizens present here include wrasse bass, bank butterflyfish, spotfin hogfish, deepwater squirrelfish, and roughtongue bass. Red grouper (Epinephelus morio), scamp (Mycteroperca phenax), and snapper here are of particular importance to commercial fisheries in the Gulf of Mexico.
Several factors help account for the existence of this unique community. The underlying drowned barrier islands provided elevated hard substrate, which is ideal for the formation of reefs. Also, the region is located along the western edge of the Loop Current that brings relatively warm water to the southern ridge, but located along a front that upwells nutrients from deeper water to fuel the relatively high productivity observed here.
Conservation Efforts
The Pulley Ridge system was classified by NOAA Fisheries as a Habitat Area of Particular Concern in 2019, granting it protection from certain damaging kinds of fishing, specifically bottom longlines. The biome is considered a deepwater refuge, a source of larval recruits, and a recruitment corridor, providing continuity for many shallower reef habitats. In July 2022, the Florida Keys National Marine Sanctuary sought to add 1,000 square miles (2,590 square kilometers) to its sanctuary to further protect the region's biodiversity. However, many organizations opposed these efforts, and the plan remained unimplemented.
The exposure of the corals of Pulley Ridge to climate change impacts will be mitigated in part by its depth. Rising surface temperatures will not be likely to penetrate here; indeed, there is no evidence of recent bleaching events on Pulley Ridge. Heavier storm action, too, will be unlikely to affect an ecosystem at this depth. However, the changing acidity of the seawater—which can be a side effect of greater oceanic absorption of excess atmospheric greenhouse gasses—could affect the reproductive and coral-building capacities of some species. This factor will have to be monitored.
Bibliography
Farrington, Stephanie, and John Reed. "About Pulley Ridge." National Oceanic and Atmospheric Administration, oceanexplorer.noaa.gov/explorations/13pulleyridge/background/aboutpr/aboutpr.html. Accessed 10 Dec. 2024.
Halley, R., et al. "Pulley Ridge—The United States’ Deepest Coral Reef?" United States Geological Survey, 2005, pubs.usgs.gov/of/2005/1213/PDF‗Files/Poster‗Session‗1/Halley-Pulley‗Ridge.pdf. Accessed 10 Dec. 2024.
Jarrett, B. D., et al. “Strange Bedfellows—a Deep-Water Hermatypic Coral Reef Superimposed on a Drowned Barrier Island; Southern Pulley Ridge, SW Florida Platform Margin.” Marine Geology, vol. 214, no. 4, pp. 295–307, doi.org/10.1016/j.margeo.2004.11.012. Accessed 10 Dec. 2024.
Klingener, Nancy. "Keys Marine Sanctuary Looks to Add Almost a Thousand Square Miles." WUSF Public Media, 13 July 2022, wusfnews.wusf.usf.edu/environment/2022-07-13/keys-marine-sanctuary-looks-add-almost-thousand-square-miles. Accessed 10 Dec. 2024.
"Pulley Ridge." Cooperative Institute for Ocean Exploration, 5 Aug. 2021, www.cioert.org/expeditions/pulleyridge. Accessed 10 Dec. 2024.
"Pulley Ridge Habitat Area of Particular Concern." NOAA Fisheries, 30 Dec. 2019, www.fisheries.noaa.gov/southeast/pulley-ridge-habitat-area-particular-concern. Accessed 10 Dec. 2024.
Reed, John K., et al. “Pulley Ridge, Gulf of Mexico, USA.” Mesophotic Coral Ecosystems, vol. 12, 2019, doi.org/10.1007/978-3-319-92735-0‗4. Accessed 10 Dec. 2024.