Transient turbid water mass reduces temperature-induced coral bleaching and mortality in Barbados.

Hazel A Oxenford,Henri Vallès

doi:10.7717/peerj.2118

Abstract

Global warming is seen as one of the greatest threats to the world’s coral reefs and, with the continued rise in sea surface temperature predicted into the future, there is a great need for further understanding of how to prevent and address the damaging impacts. This is particularly so for countries whose economies depend heavily on healthy reefs, such as those of the eastern Caribbean. Here, we compare the severity of bleaching and mortality for five dominant coral species at six representative reef sites in Barbados during the two most significant warm-water events ever recorded in the eastern Caribbean, i.e., 2005 and 2010, and describe prevailing island-scale sea water conditions during both events. In so doing, we demonstrate that coral bleaching and subsequent mortality were considerably lower in 2010 than in 2005 for all species, irrespective of site, even though the anomalously warm water temperature profiles were very similar between years. We also show that during the 2010 event, Barbados was engulfed by a transient dark green turbid water mass of riverine origin coming from South America. We suggest that reduced exposure to high solar radiation associated with this transient water mass was the primary contributing factor to the lower bleaching and mortality observed in all corals. We conclude that monitoring these episodic mesoscale oceanographic features might improve risk assessments of southeastern Caribbean reefs to warm-water events in the future.

Highlights

Coral reefs across the Caribbean have shown significant losses in live coral cover over the last five decades, even though the decline has been spatially and temporally variable (Pandolfi et al, 2003; Jackson et al, 2014)
These observations are confirmed by median tests comparing the intensity of bleaching between both events, which show highly significant differences for all five species in September/October (p = 0.0015 in all cases), for two species in February (O. annularis, p = 0.0396; P. astreoides, p = 0.0496), and just one species in June (O. annularis, p = 0.0360) (Table 1)
In this study we compared the bleaching and post-bleaching mortality responses of the dominant coral species in Barbados to two successive anomalous ocean warming events, i.e., 2005 and 2010, and considered a number of environmental factors that may mitigate the impacts of future acute warming events, the latter being expected to increase in frequency and even become annual in Barbados by 2045–50 (Van Hooidonk et al, 2015)

Summary

Introduction

Coral reefs across the Caribbean have shown significant losses in live coral cover over the last five decades, even though the decline has been spatially and temporally variable (Pandolfi et al, 2003; Jackson et al, 2014). We have witnessed increased levels of coral disease (Aronson & Precht, 2006) and substantial shifts to low relief, algal dominated reefs in many locations (Done, 1992; Hughes, 1994; Alvarez-Filip et al, 2009). These shifts have been accompanied by significant changes in ecosystem structure and function (Done, 1992; Mumby & Steneck, 2008).

Methods

Results

Discussion

Conclusion