Abstract
Coral cover throughout the Caribbean region has declined by approximately 80% since the 1970s (Gardner et al. in Ecology 86(1):174–184, 2005) attributed to a combination of environmental and anthropogenic factors, including ocean acidification, rising sea surface temperatures, increased susceptibility to disease, as well as increased frequency and strength of storms, development stress, and increased sediment and nutrient loads. Three Global Bleaching Events (GBE) coincide directly with El Niño warming phases in El Niño-Southern Oscillation cycle (1997–1998, 2009–2010, and 2014–2017). This study focuses the effects of anomalously high sea surface temperatures on Turks and Caicos Islands coral taxa during the 2014–2017 GBE. Interannual and interspecific variability in coral health offshore of South Caicos Island were evaluated between 2012 and 2018 using the CoralWatch citizen science Coral Health Chart method along belt transects at four dive survey sites. The study includes 104 site surveys conducted from 15 October 2012 to 18 July 2018. Coral health was assessed for the 35 principal coral taxa and 5646 individual corals. Data indicates that all coral taxa at the study sites were resilient to the maximum regional thermal stress during the 2014–2017 GBE, with boulder-type corals showing no significant bleaching as a result of the peak thermal stress in late 2015 and plate-type corals responding with a significant (p < 0.05) bleaching signal (i.e., coral color reductions), rebounding to pre-GBE pigmentations within months of the anomalously-high thermal stress. Boulder coral types were significantly healthier in 2017 than in 2014 when using coral color as a health diagnostic.
Highlights
Climate-change induced increases in sea surface temperatures (SSTs) and the frequency of extreme thermal stress events have resulted in widespread coral bleaching [1,2,3,4,5,6]
Coral bleaching mechanisms are linked with the unique endosymbiotic relationship between the host coral and single-celled dinoflagellates known as Symbiodinium, living within the coral polyps that provide corals with their color and 90% of their total energy through photosynthesis [7]
While the TCI site is located in the NE Caribbean and generally cooler with its closer proximity to Atlantic currents, maximum 2015 SST Anomaly (SSTA) and Degree Heating Week (DHW) for the study site were comparable with the Caribbean regions experiencing higher thermal stress, but not at the extremes found in other regions in 2015 (Fig. 4)
Summary
Climate-change induced increases in sea surface temperatures (SSTs) and the frequency of extreme thermal stress events have resulted in widespread coral bleaching [1,2,3,4,5,6]. When SSTs surpass a coral’s thermal threshold, bleaching may occur. They expel their algal symbionts, losing both their pigmentation and primary source of nutrients [7, 8]. 90% of Caribbean coral reef systems are likely to experience severe bleaching in response to climate-change induced thermal stress by 2040 [9,10,11]. Over the past three decades, coral cover throughout the Caribbean has declined by approximately 80% [12].
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