Abstract
Coral reefs are threatened by climate change on a global scale with thermal-stress events and mass coral bleaching being widely reported. The reefs off the east coast of Brazil (and other turbid areas) have, however, historically escaped such thermal-stress events, with relatively low levels of background coral mortality (5-10%). This has recently changed. Here we show that, in 2019, degree heating weeks (DHW) of 19.65 coincided with catastrophic declines in coral cover, especially in the major reef building hydrocoral Millepora alcicornis. The decline was due to bleaching associated with exposure to high temperature stress culminating in DHW values exceeding 15 for a period of 50 days. At two independent sites, surveys showed upwards of 83.5 9.0% and 89.1 3.9% mortality, and at a third site showed relatively lower (albeit still high), mortality rates of 43.3 12.0% were recorded. The mass die-off in 2019 is unprecedented in the South Atlantic reefs and coincides with increased heating events.
Highlights
A large proportion of all marine life is supported by coral reefs (Paulay, 1997)
Records were broken with the highest single day temperature documented since 1989 and the highest ever recorded number of degree heating weeks (DHW) in the region (NOAA Abrolhos reef station)
The highest DHW value recorded at the Abrolhos reef station was 19.65, from May 10th, 2019
Summary
A large proportion of all marine life is supported by coral reefs (Paulay, 1997) Such ecosystems benefit, either directly or indirectly, approximately 500 million people around the globe (Burke et al, 2011). Either directly or indirectly, approximately 500 million people around the globe (Burke et al, 2011) These ecosystems, are under direct threat, with climate change being identified as the major force affecting coral health on a global scale (Hughes et al, 2017). A number of reef “oases” have been identified at sites that positively deviate from regional means (Guest et al, 2018) In these sites, several physical and biological mechanisms allow corals to survive and even thrive despite the global increases in sea surface temperatures (Côté and Darling, 2010).
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