In 2013, the remote Tubbataha Reefs UNESCO World Heritage Site, in the western Philippines, experienced two ship groundings within four months: the USS Guardian (USSG), a US military vessel, and the Min Ping Yu (MPY), an illegal Chinese fishing vessel. Monitoring recovery in these pristine coral atolls began in 2014, by examining recovery of hard coral within grounding impact footprints and undamaged control sites. Coral disease assessments were undertaken in 2015, to test the hypothesis that acute catastrophic physical injury increased susceptibility to infectious diseases, resulting in long-term impacts. High wave energy and a steep slope removed debris quickly at the USSG site, whereas a large debris field has persisted at the more sheltered and gently sloping MPY site.
Results/Conclusions
Hard coral cover has increased at a mean rate of 3% per year within the USSG impact footprint; a rate comparable to that of control sites and driven by both recruitment of juvenile colonies and regrowth of surviving colonies. In contrast, hard coral cover increase has been negligible within the unstable rubble-dominated MPY site (-0.5%) despite recruitment, as recruits fail to persist over time. Coral disease was dominated by white syndromes (WS), a taxonomically and geographically widespread group of infectious diseases characterized by rapid tissue loss. Two years post-grounding, WS prevalence was 3x-7x higher within the grounding footprints (USSG WS prevalence, grounding footprint: 13.5%; MPY WS prevalence, grounding footprint: 7.9%) than within remote undamaged control sites (USSG WS prevalence, control site: 1.5%; MPY WS prevalence control site: 2.2%). These results support our hypothesis that grounding-induced massive physical injuries were associated with subsequent high prevalence of disease in surviving corals. Recovery trajectories from these two events appear strongly influenced by movement of each ship during and after grounding, as well as site-specific wave-influenced persistence of rubble and debris. Our assessments suggest that localized pockets of high disease prevalence within the impact footprint may be a long-term and potentially persistent effect of these grounding events.