Lophelia pertusa landscapes and megafaunal biotopes on the Blake Plateau off the southeastern U.S. and in the northeastern Gulf of Mexico

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Off eastern North America, Lophelia pertusa reefs are known from one locality off Sable Island, Nova Scotia, one locality on the west wall of Oceanographer Submarine Canyon, and along the Blake Plateau from Cape Hatteras to South Florida. Earlier indications of Lophelia coral at two localities in the northeastern Gulf of Mexico have recently been confirmed, as well, by submersible observations. Along the Blake Plateau from North Carolina to Florida; nearly all Lophelia reefs documented by underwater exploration align closely with the high velocity core of the Gulf Stream. The relative ubiquity of Lophelia reefs in this area contrasts markedly with the apparent near absence of this deep-water coral in the province of major submarine canyons, from Virginia to New England, a region of the continental slope that has been extensively explored by submersible, camera sled and ROV, and extensively sampled by bottom trawl. Off the U.S. southeastern coast, Lophelia biotopes and associated megafaunal taxa have been explored and sampled by our research team in a series of six subsea missions using the DSRV Johnson-Sea-Link and the U.S. Navy NR-1 submersibles, supplemented by remotely deployed sampling from surface vessels. Direct visual, video, and digital still camera documentation of Lophelia biotopes has revealed three distinct Lophelia landscapes. What we term “prime high reef landscape' occurs on the narrow northern tail of the Blake Plateau in the vicinity of Cape Lookout, NC, between depths of 350-500 m, where bottom currents are generally 0.25-0.50 m/sec, but are often accelerated to 0.75-1.2 m/sec over the living reef and the underlying mounds (presumed fossil coral bioherms). This prime high reef landscape comprises nearly pure stands of tall (up to 4 m), robust, densely-branched Lophelia bushes, with few other megafaunal invertebrates attached to the substrate. Prime reefs form on complex series of closely-set ridges and mounds, separated by deep (5-10m) narrow swales. Lophelia preferentially populates the up-current flanks and crests of the mounds. The uppermost coral bushes, probably the fastest growing colonies, display an upright growth form (to 3 m), with long thin branches, widely spaced calices, and limited anastomosing of branches. Much of the coral forming prime reef is alive, based on its white coloration, and close-up imaging documenting live feeding polyps. Live coral at the base of the colonies grows into a much denser matrix of thick coral, interconnected branches, abundantly populated by small secondary Lophelia polyps budding off from mother polyps. Prime reef is surrounded by dense accumulations of mostly dead Lophelia rubble, extending up to several hundred meters from the living colonies.