A Likely Offshore Refuge for an Endangered Caribbean Coral (A. cervicornis) in Honduras

Large-scale impacts on coral reefs due to global climatic change are projected to increase dramatically. Also suitability of many areas for reef growth is decreasing leading to the search for particular settings that might serve as refugia and maintain strong coral populations. We examine this hypothesis in Honduras. Dense coral thickets containing high numbers of endangered coral Acropora cervicornis occur on offshore banks but are rare on the fringing reef on nearby Roatan. Geomorphological setting and community dynamics were evaluated and monitored from 1996-2005. A model of population dynamics was developed to test assumptions derived from monitoring. Coral cover on the fringing reef declined in 1998 from \u3e30% to \u3c20%, but the banks maintained areas of very dense coral cover (32% cover by A. cervicornis on the banks but \u3c1% on the fringing reef). Bathymetry from satellite images showed the banks to be well-separated from the fringing reef, making asexual connectivity between banks and fringing reef impossible but protecting the banks from direct land-runoff during storms. Exposure to SE tradewinds also causes good flushing. Only four A. cervicornis recruits were recorded on the fringing reef over six years. Run-off associated with hurricanes caused greater mortality than did bleaching in 1998 and 2005 on the fringing reef, but not on the banks. Since 1870, our analysis suggests that corals on the banks may have been favored during 17 run-off events associated with tropical depressions and storms and potentially also during 5 bleaching events, but this is more uncertain. Our model suggest that under this disturbance regime, the banks will indeed maintain higher coral populations than the fringing reef and supports the assumption that offshore banks could serve as refugia with the capacity to subsidize depleted mainland populations