Increasing thermal stress for tropical coral reefs: 1871–2017

Abstract

Tropical corals live close to their upper thermal limit making them vulnerable to unusually warm summer sea temperatures. The resulting thermal stress can lead to breakdown of the coral-algal symbiosis, essential for the functioning of reefs, and cause coral bleaching. Mass coral bleaching is a modern phenomenon associated with increases in reef temperatures due to recent global warming. Widespread bleaching has typically occurred during El Niño events. We examine the historical level of stress for 100 coral reef locations with robust bleaching histories. The level of thermal stress (based on a degree heating month index, DHMI) at these locations during the 2015–2016 El Niño was unprecedented over the period 1871–2017 and exceeded that of the strong 1997–1998 El Niño. The DHMI was also 5 times the level of thermal stress associated with the ‘pre-industrial’, 1877–1878, El Niño. Coral reefs have, therefore, already shown their vulnerability to the modest (~0.92 °C) global warming that has occurred to date. Estimates of future levels of thermal stress suggest that even the optimistic 1.5 °C Paris Agreement target is insufficient to prevent more frequent mass bleaching events for the world’s reefs. Effectively, reefs of the future will not be the same as those of the past.

Endosymbiont diversity and community structure in Porites lutea from Southeast Asia are driven by a suite of environmental variables

“…They provide critical ecological services, buffering against storm impact and mitigating the risk of flooding by reducing wave energy (Heery et al 2018). However, these reefs are increasingly subjected to the negative impacts of coastal urbanisation and climate change (Fabricius 2005;Hoegh-Guldberg et al 2007;Carpenter et al 2008;Lough et al 2018;Toh et al 2018). Singapore's reefs, in particular, are threatened by decades of land reclamation and coastal development, resulting in high sedimentation rates and reduced light levels (Chou 1992;Dikou and Woesik 2006;Lai et al 2015;Chow et al 2019).…”

Reef‐Scale‐Dependent Response of Massive Porites Corals From the Central Indian Ocean to Prolonged Thermal Stress: Evidence From Coral Sr/Ca Measurements

“…The Indian Ocean is currently warming faster than any other ocean basin with maximum warming occurring in its western part (Pfeiffer et al, 2017;Roxy et al, 2014). The general warming trend in combination with several moderate and severe warm periods has led to rapid decline of coral reefs not only in the Indian Ocean (Ateweberhan et al, 2011;Manzello, 2010;Sheppard et al, 2012) but also worldwide (e.g., Hoegh-Guldberg, 1999;Hughes et al, 2003;Lough et al, 2018). Usually, reef-building corals grow within the 18°C mean annual sea surface temperature (SST) isotherm, which is generally between 30°N and 30°S (Bradley, 2015), and they grow best between 25°C and 29°C (Kinsman, 1964).…”

Paradise lost: End‐of‐century warming and acidification under business‐as‐usual emissions have severe consequences for symbiotic corals

“…Worldwide, coral health and growth have already significantly decreased over the last decades, often as a result of climate change (Baumann et al, 2019;Cantin, Cohen, Karnauskas, Tarrant, & McCorkle, 2010;Cooper, De'ath, Fabricius, & Lough, 2008;Mellin et al, 2019;Perry et al, 2015). Our study indicates that this pattern will become increasingly problematic in the future as conditions worsen (van Hooidonk et al, 2016;Lough, Anderson, & Hughes, 2018), unless corals are able to adapt rapidly. The acclimation or adaptation capacity of symbiotic corals to environmental change is uncertain (Berkelmans & van Oppen, 2006;Pandolfi, Connolly, Marshall, & Cohen, 2011;Sully, Burkepile, Donovan, Hodgson, & van Woesik, 2019;Wright et al, 2019), and differs between species .…”