Abstract
Coral bleaching events are globally occurring more frequently and with higher intensity, mainly caused by increases in seawater temperature. In Tayrona National Natural Park (TNNP) in the Colombian Caribbean, local coral communities are subjected to seasonal wind-triggered upwelling events coinciding with stronger water currents depending on location. This natural phenomenon offers the unique opportunity to study potential water current-induced mitigation mechanisms of coral bleaching in an upwelling influenced region. Therefore, coral bleaching susceptibility and recovery patterns were compared during a moderate and a mild bleaching event in December 2010 and 2011, and at the end of the subsequent upwelling periods at a water current-exposed and -sheltered site of an exemplary bay using permanent transect and labeling tools. This was accompanied by parallel monitoring of key environmental variables. Findings revealed that in 2010 overall coral bleaching before upwelling was significantly higher at the sheltered (34%) compared to the exposed site (8%). Whereas 97% of all previously bleached corals at the water current-exposed site had recovered from bleaching by April 2011, only 77% recovered at the sheltered site, but 12% had died there. In December 2011, only mild bleaching (<10% at both sites) was observed, but corals recovered significantly at both sites in the course of upwelling. No differences in water temperatures between sites occurred, but water current exposure and turbidity were significantly higher at the exposed site, suggesting that these variables may be responsible for the observed site-specific mitigation of coral bleaching. This indicates the existence of local resilience patterns against coral bleaching in Caribbean reefs.
Highlights
Climate change can impede scleractinian corals in their role as reef ecosystem engineers [1,2] mainly because mass coral bleaching, one of the main consequences of climate changeinduced ocean warming, negatively impacts growth and health of affected corals [3].In 2005, such a mass coral bleaching event affected 80% of all Caribbean reef corals, after which 40% died, when thermal stress exceeded any recorded data on seawater temperature of the last 20 years [4]
During the first coral bleaching monitoring campaign, significant differences were found between sites (Table 1) indicating that the proportion of overall bleached corals was significantly smaller at the exposed compared to the sheltered site (8% vs. 34%, respectively; Fig. 2)
Sites had a different community composition with O. faveolata and O. franksi only occurring at the sheltered site (Fig. 3)
Summary
In 2005, such a mass coral bleaching event affected 80% of all Caribbean reef corals, after which 40% died, when thermal stress exceeded any recorded data on seawater temperature of the last 20 years [4]. This particular mass coral bleaching event was later termed the ‘‘Caribbean Crisis’’ [5]. During the ‘‘Caribbean Crisis’’ in 2005, only 1 – 5% of the coral cover in TNNP was affected by bleaching with a negligible mortality of below 1% [6]
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