Great Coral Barrier Bleaching after Cyclone Debbie
After the passage of Cyclone Debbie over East Australia, a massive bleaching event over the Great Coral Barrier has been remotely observed from Satellite images. The same event is being assessed by in-situ measurements which seem confirming the severe event.
Thanks to the spatial and temporal resolution Copernicus Sentinel-2 satellite has been demonstrated to be an important mean for Coral Reefs study applications (cf. https://sen2coral.org/). Recent images acquired by the ESA Copernicus satellites show indeed an important bleaching event for the Australian Great Coral Barrier.
Sentinel-2A True Color Image (1 April 2017)
Images below show the high level of detail offered by Sentinel-2 images. The algae leave the coral’s tissue and are dispersed in water.
When stressed corals expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called Coral Bleaching. When a coral bleaches, it is not dead. Corals can normally survive a bleaching event, but they are under more stress and are subject to mortality. Usually warmer water temperatures can result in coral bleaching but not only.
Cyclones generate strong winds and destructive ocean swells that can damage delicate corals. On the other hand cyclonic weather conditions usually cool down ocean temperatures which could bring relief to the reef in wake of record ocean temperatures last months. Unfortunately according to scientists the cooling effect was not enough to prevent further mass bleaching and, on the contrary, the intense winds seem having seriously damaged the Queensland reefs.
Sentinel-3 OLCI image showing the Cyclone Debbie approaching the Australian shores. (28 March 2017)
References:
[1] http://oceanservice.noaa.gov/facts/coral_bleach.html
[2] http://www.news.com.au/technology/environment/natural-wonders/tragic-barrier-reef-as-youve-never-seen-it-after-debbie-reduced-it-to-rubble/news-story/4fe66356bfcfaa8bf503a7d77e15db78
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