While the terms “coral reef” and “high seas” are rarely combined in the same sentence, reef-building corals are found in Areas Beyond National Jurisdiction (ABNJ), the high seas. A study that has been published in the Frontiers in Marine Science identified 116 coral reefs in the Atlantic and Pacific Ocean, most of them located outside Marine Protected Areas (MPAs).

There is currently no comprehensive legal framework for the establishment of MPAs in ABNJ. Rather, initiatives to protect critical habitats on the high seas remain scattered throughout the legal mandates of organizations with different management purposes…. Yet, high seas MPAs are possible…. For example, the member countries of the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR) and the Convention on the Conservation of Antarctic Marine Life (CCAMLR) have established MPAs in ABNJ of the North Atlantic and Southern Ocean, respectively While these MPAs provide important advances in protecting biodiversity on the high seas, they still only cover a very small portion of the international ocean. 

David Wagner et al., Coral Reefs of the High Seas: Hidden Biodiversity Hotspots in Need of Protection, Frontiers in Marine Science, Sept. 14, 2020

See also Coral Reefs on the High Seas Coalition