The 2014–2017 global-scale coral bleaching event: insights and impacts

Abstract

2014-2017 was an unprecedented period of successive record-breaking hot years, which coincided with the most severe, widespread, and longest-lasting globalscale coral bleaching event ever recorded. The 2014-2017 global-scale coral bleaching event (GCBE) resulted in very high coral mortality on many reefs, rapid deterioration of reef structures, and far-reaching environmental impacts. Through the papers in this special issue of Coral Reefs entitled The 2014-2017 Global Coral Bleaching Event: Drivers, Impacts, and Lessons Learned, as well as papers published elsewhere, we have a good analysis of the 2014-2017 GCBE and its impacts. These studies have provided key insights into how climate change-driven marine heatwaves are destroying coral reef ecosystems: (a) The 2014-2017 GCBE is unique in the satellite record in its spatial scale, duration, intensity, and repetition of bleaching. (b) The impacts have been the most severe ever seen at many reefs. (c) Timing of observations matters and needs to be considered during the analysis of impacts. (d) On both global and local scales, the intensity of heat stress and impacts varied. (e) We continue to see important differences among and within coral taxa, with key roles played by algal symbionts and the microbiome. (f) Heat stress and bleaching both play a role in subsequent disease, which plays a key role in mortality. (g) Impacts ripple far beyond corals, with significant changes to the fish and invertebrate community that may last decades. (h) The structure of both individual coral's skeletons and entire reefs has been eroded much more quickly than previously realized. (i) The 2014-2017 GCBE provided little support for the proposed ''lifeboat'' hypothesis, whereby deep or mesophotic reefs serve as a means of coral reef salvation. (j) While marine protected areas (MPAs) provide protection from local stressors, they not only do not protect reefs from global-scale stressors, but also here is also little evidence they provide significant resilience. Keywords Coral bleaching Á Heat stress Á Coral Reef Watch Á CoralTemp Á Marine heatwave Á Symbionts Á Microbiome Á Coral disease Á El Niño Á ENSO

Coral bleaching patterns are the outcome of complex biological and environmental networking

“…Global degradation of coral reefs is fast becoming a legacy of the Anthropocene. Continued declines in reef health worldwide through accelerated industrialization, urbanization, and agriculture (Lapointe, Brewton, Herren, Porter, & Hu, ; Osborne et al, ) have been punctuated by heat wave‐driven catastrophic coral mortality events that have grown in intensity and frequency under climate change (Eakin, Sweatman, & Brainard, ; Hughes et al, , ). Extreme heat wave events conspicuously manifest as mass coral bleaching—the process whereby large extents of coral rapidly pale through loss of their algal endosymbionts (e.g., Glynn, ; Suggett & Smith, ) via destabilization of the coral–algal symbiosis (e.g., Davy, Allemand, & Weis, ; Matthews et al, ; Smith, Suggett, & Baker, ; Weis, ).…”

“…Instances of mass coral bleaching have been reported since the early 1980s, but it was not until 1998, just 3 years after the inception of Global Change Biology , when the first El Niño‐driven global heat wave event resulted in catastrophic mass coral mortality worldwide (Eakin et al, )—1998 arguably placed coral bleaching on the world stage, kick‐starting intensive efforts to understand the causes and effects (Cziesielski, Schmidt‐Roach, & Aranda, ). Over 2,600 papers ( ISI Web of Science search “coral” AND “bleaching,” August 15, 2019) have been published since 1998, whereby continually expanding knowledge gained has been periodically transformed by new tools and technologies that particularly advanced bleaching observations in nature or unlocked the biological mechanisms at play.…”

Density of coral larvae can influence settlement, post-settlement colony abundance and coral cover in larval restoration

“…Coral reefs are globally significant ecosystems that are declining from cumulative threats including climate change, destructive fishing practices, pollution and poor water quality 1,2 . In many regions, significant areas of coral reef habitat have been lost 3 , while in others the surviving corals are sparsely distributed and unable to recover within reprieve periods between significant disturbance events 4,5 . These accelerating global declines require increased conservation and management action to protect coral reefs, including development of innovative measures for active coral reef restoration [6][7][8][9] .…”

Thermal Stress and Resilience of Corals in a Climate-Changing World

“…Other conservation measures under consideration include designing better marine protected areas (MPAs) [143] or networks of MPAs [144][145][146], taking into consideration larval dispersal, connectivity and distribution patterns in areas with thermally tolerant corals [147] and including 'refugia' in areas where coral reefs have proven to be resilient to climate change [21,43,148,149]. This might help avoid the "protection paradox" in MPAs, in which vulnerable species are protected from local pressures, like fishing; yet while these species recover, they might be more sensitive to global pressures, like bleaching events [144].…”

“…The impact of increasing greenhouse gases in the atmosphere is leading to a global increase in seawater temperatures that has caused mass bleaching events [12,[14][15][16][17]. These global bleaching events are becoming more frequent (1998, 2010 and 2014-17) and severe [14,16,[18][19][20][21][22], leaving coral reefs vulnerable and unable to recover. The 2014-2017 mass bleaching event, which lasted 36 months and spanned four calendar years, was the longest-lasting, most widespread, and probably most damaging event on record [21][22][23][24][25][26][27][28][29], and stands out as unique by spanning all phases of the El Niño-Southern Oscillation cycle of 2017, being the warmest non-El Niño year ever recorded [21,30].…”