Adding insult to injury: Ship groundings are associated with coral disease in a pristine reef.

L J Raymundo,A M Kerr,W L Licuanan,Even Moland

doi:10.1371/journal.pone.0202939

Abstract

In 2013, the remote Tubbataha Reef 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. Here, we present the results of coral disease assessments completed two years post-grounding and recovery patterns monitored annually within these grounding sites. Site assessments were undertaken in three distinct zones: ‘ground zero’, where reef was scoured to its limestone base by direct ship impact; the ‘impact border’, containing surviving upright but damaged, abraded and fragmented colonies injured during ship movement; and undamaged ‘control’ sites, remote from the ship groundings but located on the same atoll. Coral diseases were dominated by white syndromes, and prevalence was an order of magnitude higher within the impact border zones than within the other zones two years after the events. Hard coral cover has steadily increased at a mean rate of 3% per year within the scoured USSG site at a rate comparable to control sites. In contrast, recovery has been negligible within the rubble-dominated MPY site, suggesting that substrate quality strongly influenced recovery processes such as recruitment, as larvae do not survive well on unstable substrates. Long-term recovery trajectories from these two grounding events appeared strongly influenced by movement of the ship during and after each event, and site-specific wave-influenced persistence of rubble and debris. High prevalence of coral disease among damaged but surviving colonies two years post-grounding suggested long-term impacts which may be slowing recovery and creating localized pockets of higher persistent disease prevalence than that of the surrounding population.

Highlights

In 2013, two ship groundings occurred within four months on the remote and largely inaccessible atolls of the Tubbataha Reefs Natural Park (TRNP), in the western Philippines
Hard coral cover (HCC) steadily increased from 2014 onwards (Fig 2a), ranging from 1% to 4% per year per plot (Table 1) and grounding site plots followed similar growth trends to control plots (Hadj = 1.04; p = 0.406). An exception to this trend was a visible decrease in HCC in all USS Guardian (USSG) sites in 2015, though growth has been positive since that time (Table 1, Fig 2a, S1 Table)
This study provides the first report, to our knowledge, of long-term impacts of coral disease and physical injury from multiple ship groundings on a pristine coral reef

Summary

Introduction

In 2013, two ship groundings occurred within four months on the remote and largely inaccessible atolls of the Tubbataha Reefs Natural Park (TRNP), in the western Philippines. On April 8, the Chinese fishing vessel, Min Ping Yu (MPY), ran aground along the southeastern margin of the northern atoll, damaging an additional 3,902 m2 of coral garden reef community [1]. The shallow communities of both grounding sites were scoured to the limestone bedrock and large debris fields were created by ship movement. The MPY site was relatively sheltered gentle slope, the boat was extracted in 11 days, but hit the reef three times before coming to rest (Fig 1). These conditions resulted in the persistence of rubble and debris within the grounding footprint

Methods

Results

Conclusion