Modelling dispersal and connectivity of broadcast spawning corals at the global scale

Aim We develop the first global model of connectivity for a generic broadcast spawning coral, and compare the results to connectivity estimates from genetic studies, general biogeographic patterns and theories. We also derive various connectivity indices' describing relative isolation and source potential between locations.

LocationModelled oceans 47 degrees S-47 degrees N.

Methods Dispersal of model coral larvae' was simulated over 8 years using an individual-based biophysical dispersal model driven by 1/12 degrees-resolution surface ocean current data and incorporating individual trait variability (e.g. a phased pre-competency period). Source and arrival locations of modelled larvae on suitable reef habitat gave standardized dispersal paths and relative levels of connectivity.

ResultsIn the model c. 50% of connections occurred within 50-100km, with rarer dispersal between regions linking entire oceans in a stepping stone' fashion. The central Pacific was an almost complete barrier to dispersal, only rarely breached westward from the Galapagos to Marquesas Islands. Areas showing strong isolation also included Hawaii, Easter Island, the Red Sea and the eastern Atlantic. The Indo-West Pacific and Great Barrier Reef showed the highest levels of connectivity, with secondary peaks in the western Indian Ocean, corresponding to areas of enriched coral diversity. The central Indo-Pacific diversity hotspot was overall a greater source than sink for dispersal.

ConclusionsThis study provides a global view of connectivity that complements genetic and biogeographic work as well as providing a number of novel findings relevant to biogeographic theories (e.g. the central Indo-Pacific as a dispersal source; Johnston Atoll as the sole stepping-stone' into Hawaii). Discrepancies with proposed connectivity patterns (e.g. one-way, westward, connectivity across the central Pacific) present hypotheses for future research. The model represents an effective tool for exploring the factors controlling connectivity on this scale and the effects of climate change on future connectivity, and will also aid predictions of future reef distributions.