Foraminifera of petroleum platforms, Louisiana shelf, Gulf of Mexico

Species of benthic foraminifera presumably colonized the bacteria- and diatom-rich biofilms on the metallic surfaces of Louisiana-shelf petroleum platforms soon after their emplacement. At present, however, most underwater platform legs are covered by a thick growth of macrofoulers, predominantly barnacles and bivalves. Scraped samples from five such platforms (water depth 16-61 m) yielded 104 species of benthic foraminifera 44 of them with attached individuals. Among the obligate sessile species, Dyocibicides biserialis and Planorbulina mediterranensis were especially widespread. This group of epibionts also includes Calcituba polymorpha, Carpenteria candei, Cornuspiramia antillarum, Lepidodeuterammina ochracea, Nubeculinita inhaerens, Planorbulina acervalis, Planorbulinoides retinaculatus, Sagenina divaricans, Webbina bonairensis, and Webbina rugosa. The platforms are habitat islands; the surrounding soft, clastic substrate does not support the growth of most sessile species. The putative source areas of these colonists of Louisiana platforms are carbonate hardgrounds to the west (banks or reefs formed over salt diapirs) and other platforms. The foraminiferal species diversity on the platforms is most likely controlled by their distances from these sources, and the dimensions of the settlement surfaces. The eastward transport of propagules in summer by the Louisiana-Texas Coastal Current facilitates the species migration. (C) 2013 Elsevier B.V. All rights reserved.