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We ask the question, what are the patterns of genetic affinity in these coral populations. We sampled coral tissue from populations of two species occurring on oil and gas platforms: Madracis decactis hermatype and Tubastraea coccinea invasive ahermatype. The entire population of M. Genetic connectivity among M. Connectivity increased again in the eastern sector, indicating isolation between the populations from different sides of the Mississippi River Transects 3 and 4.
A point-drop in genetic affinity relatedness at the shelf edge south of Terrebonne Bay, LA indicated a population differing from all others in the northern GOM. Genetic affinities among T. Very low genetic affinities off Mobile, AL indicated a dramatic difference between those populations and those west of the Mississippi River, apparently a formidable barrier to larval dispersal. Prior to the s, the bottom of the Gulf of Mexico GOM was characterized primarily by terrigenous, sandy muds with low habitat diversity [1] , [2].
During that decade, offshore drilling for oil and gas began there and production platforms grew steadily in number, spreading southward across the continental shelf. Those platforms served as substrate for colonization of numerous marine organisms, and this process has continued [3] โ [8]. These production platforms extend up from the bottom into the atmosphere, creating an island and providing hard substrate through all depths of the water column [9] that would otherwise not be available to benthic or demersal marine organisms.
It has been estimated that a ft. In earlier studies, we and others have documented the presence of both hermatypic zooxanthellate, reef-building and ahermatypic azooxanthellate, non-reef-building scleractinian corals on many of these platforms [5] , [10] โ [17].
