Inferring probable dispersal of Flower Garden Banks Coral Larvae (Gulf of Mexico) using observed and simulated drifter trajectories

We investigated likely coral larvae dispersal in the Gulf of Mexico by means of a combination of satellite-tracked drifters and simulated currents. Drifter data were collected during spawning events in 1997 and 1998 at the Flower Garden Banks (FGB) and from the “Surface Current and Lagrangian Drift Program” in 1993 (Niiler et al., Surface current and langrangian-drift program. Unpublished Report, U.S. Department of the Interior, Minerals Management Service, 1997, 10pp). Observed and simulated tracks showed that likely coral dispersal is driven by five circulation modes. Mode 1 is a cyclonic motion reaching the Texas shelf and possible cyclonic motion along the shelf toward Mexico. Mode 2 is an entrainment by offshore eddies causing likely larval transport into deep water (>200 m). Mode 3 consists of a continuous eastward movement that reaches 87.5°W. Mode 4 consists of recirculating flows over or near the FGB. Mode 5 is a cross-basin transport that ends near the Florida Keys in 50–60 days. Modes 1 and 4 can bring larvae back to the FGB within 24–30 days after spawning creating conditions for self-seeding. Offshore eddies near the FGB, Modes 2 and 5, generate offshore transport that can carry coral larvae to reefs in Mexico and Florida. Only ∼43% of the drifters leave the northwestern Gulf shelf, which implies that most coral larvae can remain on the shelf through Modes 1, 3, and 4. Mode 3 suggests eastward larval dispersal and under influence of the Mississippi River plume where they can be adversely affected by low salinity, low temperature, and high sedimentation which limit recruitment on oil and gas platforms. Possible effects of hurricanes on larval dispersal include reduced travel time, considerable displacements, and physical damage by strong turbulence. Nineteen outer shelf banks were contacted by actual and simulated drifter tracks, but only 10 are suitable for coral larvae settlement given the substrate and crest depth. These 10 banks could represent a doubling of reef area relative to the FGB, i.e., 5.35 km2 shallower than 55 m, if successfully colonized by coral larvae. Drifter tracks also contacted 129 major oil and gas fixed platforms. Potential larvae recruitment by these contacts could increase the reef area in the northwestern Gulf by 38% compared to the FGB, and support eastward propagation of corals. A majority of actual and simulated drifter contacts occurs within 40 km of the FGB; contacts increased at 70 km and beyond 150 km from the FGB. This contact distribution suggest a high potential for self-seeding, and connectivity of Gulf reefs at long time scales.