The clear waters surrounding Saint John support a diverse and complex system of coral reefs.

The health of these reefs is closely tied to its component plants and animals as well as adjacent non-coral marine environments such as sandy bottoms, seagrass beds, and mangrove forests.

The monument includes 12,708 acres (51 km2) of federal submerged lands within the 3 mile (5 km) belt off Saint John, including Hurricane Hole and areas north and south of Saint John.

The USGS began extensive research in the area and scientists discovered previously unknown coral ecosystems at the submerged stems of mangrove trees in the Hurricane Hole area of the National Monument.

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