Are cyclones agents for connectivity between reefs?

Aim: Our aim was to determine whether cyclone-modified currents and winds can enhance coral larval transport between geographically separate reefs and whether connectivity could occur within the competency period of coral larvae. Location: The North West Shelf of Australia. Methods: Larval connectivity was modelled between inshore and mid-shelf reef zones in two years (1996 and 2001) when cyclones occurred around the time of coral spawning. This was contrasted with 2002, when cyclones were absent during the spawning. The effects of current and wind patterns on the dispersal of buoyant coral eggs was simulated using GCOM3D, a three dimensional hydrodynamic current model, and OILMAP, a surface wind stress model. Results: Modelling showed that larvae could disperse across the North West shelf and well beyond the parent reefs when influenced by cyclone-modified wind and current patterns. The dispersal of larvae to reefs separated by 100 km is likely to be frequent, to involve a substantial proportion of the larval population (between 63% and 86%), and to occur within 6 days (the competency period of the larvae). Simulating larval behaviour by including a buoyant phase in the larval model, where larvae are subject to surface winds, reduces connection time between reef areas by 11% to 29%. Main conclusions: Cyclones have the potential to increase the distance larvae travel and can act to rapidly connect widely separated inshore and mid-shelf reefs within the competency period of coral larvae. The buoyant phase of the coral larvae, where larvae are subject to propulsion by surface winds and subsurface currents, may enhance rapid connectivity. Our results show that periodic and extreme climatic conditions could significantly impact connectivity. In combination with larval behaviour they have important implications for connectivity time between inshore and mid-shelf reefs. © 2014 John Wiley & Sons Ltd.