Modelling coral larval dispersal across the world’s greatest marine barrier

Sally Wood1, Iliana B Baums2, Claire B Paris3, Andy Ridgwell4, William S. Kessler5 and Erica Hendy1, (1)Bristol University, Bristol, United Kingdom, (2)Pennsylvania State University Main Campus, Biology, University Park, PA, United States, (3)University of Miami, Miami, FL, United States, (4)University of California, Department of Earth Sciences, Riverside, CA, United States, (5)NOAA, Pacific Marine Environmental Laboratory, Seattle, United States
Abstract:
More than 5000 km separates the frequently disturbed coral reefs of the Eastern Tropical Pacific (ETP) from western sources of population replenishment, partially accounting for low species diversity and supressed recovery following disturbance in the region. However, the presence of a number of trans-Pacific corals in the ETP implies that some species have, at least historically, breached this expanse. It has been proposed that increased eastward currents across the central tropical Pacific during El Niño events facilitates rare cross-Pacific dispersal into the region, linking isolated ETP reefs to central Pacific larval sources. However, direct evidence for this phenomenon is lacking in corals.

Here we present output from a biophysical coral larval dispersal model which contradicts this hypothesis. The model, which employs the Connectivity Modelling System (CMS), is driven by 10 years (1997-98 plus 2003-11) of high resolution (daily 1/12°) surface oceanographic data from the HYbrid Coordinate Ocean Model (HYCOM). Only westward cross-Pacific connections occurred over the modelled period, which covers range of climatic variability; including the extreme 1997-98 El Niño as well as both central and eastern ‘type’ El Niño events. We infer that ETP coral populations decimated by this event have therefore likely recovered from local sources, limiting their genetic diversity. This finding is corroborated by genetic data from a common Pacific reef-forming coral species. We suggest that dispersal in surface-dwelling larvae is better described by local near-surface downwind flow rather than generalised upper ocean circulation patterns. We also find that the phase of ENSO exerts a strong control on patterns of inter-regional connectivity within the ETP. Changes to wind stress patterns and ENSO as a result of future climate change will therefore likely impact coral gene flow across the region, with potential implications for the resilience of reefs Pacific-wide.

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