Western boundary currents drive sun-coral (Tubastraea spp.) coastal invasion from oil platforms

Most marine species have a planktonic larval phase that benefit from the surface oceanic flow to enhance their dispersion potential. For invasive species, the interaction of environmentally resistant larvae with different flow regimes and artificial substrates can lead to complex larval dispersion patterns and boost geographic expansion. In the Southwest Atlantic, the invasive corals Tubastraea spp. (sun-coral) have been recorded biofouling on oil platforms since the late 1980s. These platforms are considered important vectors for the established populations throughout the Brazilian coast. However, we still do not know how the position of these structures relative to regional flow contribute to the natural dispersion potential of these invaders on a regional scale. Herein, we used an eddy-resolving ocean model (ROMS) and an Individual Based Model (IBM-Ichthyop) to simulate the natural dispersion patterns of sun-coral larvae from all oil platforms on Brazilian oil-producing basins, for the austral summer and winter along 6 years (2010-2015) in 90-day simulations. We found that mortality rates by advection were significantly higher during the winter (p = 0.001) and when sources of larvae were compared throughout this season (p = 1.9 × 10^-17). The influence of two western boundary currents and persistent eddy activity contribute to the dispersal of larvae to distances up to 7000 km. The effectiveness of each oil-producing basin as vectors for the entire Brazilian coastline, measured as the percentage of larval supply, highlights the importance of the northern Ceará (59.89%) and Potiguar (87.47%) basins and the more central Camamu (44.11%) and Sergipe-Alagoas (39.20%) basins. The poleward shift of the Southern branch of the South Equatorial Current during the winter causes larvae released from the Sergipe-Alagoas and Camamu basins to enter the North Brazil Current, expanding their dispersion towards the north. The Brazil Current disperses larvae southwards, but strong mesoscale activity prevents their dispersion to the coast, especially for those released from the oil platforms on Campos and Santos basins. Within this complex hydrodynamic setting, a few source areas, like those in the Sergipe-Alagoas and Camamu basins, can potentially contribute to the spread of larvae along nearly all the Brazilian coast. Therefore, oil platforms act as possible chronic sources of sun-coral propagules to the coast, emphasizing the urgency for a more detailed set of actions to control and monitor these invasive exotic species.