Distribution of corals colonizing oil and gas platforms in the northwestern Gulf of Mexico: a preliminary report
Abstract
The Flower Garden Banks (FGB), Gulf of Mexico (GOM), are highly isolated corals reefs. The
surrounding continental shelf possesses ~3,800 oil/gas platforms. Questions: To what degree are
corals expanding their geographic range through the Gulf via these platforms, and what are their
genetic affinities to neighboring systems. Thirteen platforms were surveyed initially in the
vicinity of the FGB. Coral settlement racks were deployed to determine levels of recruitment.
Tissue samples of dominant corals were collected for genetic analysis and analyzed via AFLP.
Recruitment on the platforms was compared with that from similar racks implanted on the FGB.
Two cross-shelf transects were also taken off Port Aransas, Texas and Lake Sabine, Louisiana, to
assess corals on platforms. Eleven coral species were found—nine hermatypic, and two
ahermatypic—the most abundant being Madracis decactis and Diploria strigosa, and Tubastraea
coccinea, respectively. Most species were characteristic of later sere communities; Agaricia and
Porites spp. were notably rare or absent, respectively. There was no relationship between coral
abundance and distance from the FGB. Abundance and diversity were correlated with platform
age. Coral recruitment was high on the FGB but rare on the platforms. Spat species composition
was normal on the FGB (Agaricia and Porites spp.) but atypical on platforms near the FGB,
characterized by Tubastraea coccinea and Madracis decactis. The western limit of scleractinian
corals on platforms occurred ~60 km SE of Port Aransas, Texas, at the shelf edge, but
ahermatypic corals were abundant throughout this region. Ahermatypic corals abounded starting
~120 km offshore, with hermatypes occurring 180–210 km, near the shelf edge. No corals were
found between 60 and 120 km offshore. Populations of D. strigosa on the FGB and platforms
were highly self-contained, with minimum genetic connectivity. M. decactis populations were
more genetically homogeneous. Contrary to current larval dispersal theory, this brooder was
highly effective at dispersing to neighboring habitats; the broadcaster was not.