Marine heatwave causes unprecedented regional mass bleaching of thermally resistant corals in northwestern Australia

Abstract

In 2015/16, a marine heatwave associated with a record El Niño led to the third global mass bleaching event documented to date. This event impacted coral reefs around the world, including in Western Australia (WA), although WA reefs had largely escaped bleaching during previous strong El Niño years. Coral health surveys were conducted during the austral summer of 2016 in four bioregions along the WA coast (~17 degrees of latitude), ranging from tropical to temperate locations. Here we report the first El Niño-related regional-scale mass bleaching event in WA. The heatwave primarily affected the macrotidal Kimberley region in northwest WA (~16°S), where 4.5–9.3 degree heating weeks (DHW) resulted in 56.6–80.6% bleaching, demonstrating that even heat-tolerant corals from naturally extreme, thermally variable reef environments are threatened by heatwaves. Some heat stress (2.4 DHW) and bleaching (<30%) also occurred at Rottnest Island (32°01’S), whereas coral communities at Ningaloo Reef (23°9’S) and Bremer Bay (34°25’S) were not impacted. The only other major mass bleaching in WA occurred during a strong La Niña event in 2010/11 and primarily affected reefs along the central-to-southern coast. This suggests that WA reefs are now at risk of severe bleaching during both El Niño and La Niña years.

Environmental and physiochemical controls on coral calcification along a latitudinal temperature gradient in Western Australia

“…Temperatures at the depth where our experimental corals were growing in Coral Bay (2-3 m) did not exceed their maximum monthly mean (MMM) of 27.4°C (Le Nohaïc et al, 2017) and no visible signs of bleaching (i.e., paling due to loss of photosynthetic pigments and/ or symbionts) were observed throughout the study (authors © observations). These multiple lines of evidence demonstrate that thermal stress was not the main cause of the observed changes in pH cf and temperature-growth trends.…”

The Future of Coral Reefs Subject to Rapid Climate Change: Lessons from Natural Extreme Environments

“…Furthermore, thermal history has been shown to influence bleaching susceptibility of corals harboring the same symbiont type, with more variable temperature environments enhancing heat resistance . During the first documented regional-scale bleaching event in the Kimberley in the austral summer of 2016 (Hughes et al, 2017), corals were more severely bleached (Le Nohaïc et al, 2017) and experienced much greater mortality (V. Schoepf, unpublished data) at the less-variable subtidal site on Shell Island.…”

The Role of Clouds and Surface Heat Fluxes in the Maintenance of the 2013–2016 Northeast Pacific Marine Heatwave

“…MHWs often have devastating ecological and economic impacts, which can increase in severity with the length and intensity of the MHW. Anomalously warm SSTs can cause coral bleaching (Hughes et al, 2017;Le Nohaïc et al, 2017), movement of marine species to cooler water (Cavole et al, 2016;Oliver, Benthuysen, et al, 2018;Wernberg et al, 2016), mass species die offs (Jones et al, 2018;Oliver, Benthuysen, et al, 2018;Garrabou et al, 2009), and harmful algal blooms (McCabe et al, 2016). For the NE Pacific MHW in particular, the harmful algal bloom associated with the event was the largest ever recorded and caused closures of many lucrative fisheries in the U.S. Pacific Northwest (Cavole et al, 2016;McCabe et al, 2016).…”