Bleaching Of The Great Barrier Reef Seen From Space

Bleaching can be seen on the Great Barrier Reef using the Sentinel-2 Satellite. ESA

Josh Davis 29 May 2017, 16:50

Even from space, researchers are able to watch the Great Barrier Reef bleaching event. For the first time, scientists from the European Space Agency (ESA) have documented patches of the reef turning white.

The Sentinal-2 mission comprises of twin satellites that are in the same polar orbit at 180° to each other. This means that they can both photograph exactly the same patch of land at the same resolution and orbit, allowing researchers to see how things might be changing over time. Due to the incredible resolution from these satellites, this has granted scientists the first chance to observe coral bleaching as it's happening from space.

It is difficult to see the process occurring from orbit. Just because a patch of the ocean is white, does not mean that bleaching has happened, as this could be down to a number of reasons. This is why it is important to have the twin satellites look at the same point over a period of time, as it lets the scientists spot the tell-tale pattern.

Over a period of a few weeks at the beginning of the year, the researchers at ESA were able to watch as the coral turned from a dark color, to white. After a few weeks, the bright white coral then darkened again, but it is difficult to judge exactly what is going on here. This is because either one of two things is happening: the coral has either recovered and gone back to normal, or it has died and become overgrown with algae.

While the Great Barrier Reef has gone through bleaching events in the past, these have typically occurred at least every decade or so, giving the coral ample time to recover, and allowing the reef to endure. But in the last two years, the reef has undergone an unprecedented two successive bleaching events.

Coral bleaching does not mean that the coral dies. It occurs when the tiny photosynthetic organism that coral holds onto, and which gives the coral not only the food it needs to survive, but also its bright and beautiful colors, is ejected.

This happens when the coral becomes stressed, such as when the water temperature rises too much. By getting rid of this organism, the coral has no means of getting energy, and turns ghostly white. Yet the coral can still survive. If the water temperature drops within a few weeks, then the coral can take back up the organisms and return to normal.

Sentinel-2 cannot tell whether or not this is happening, though recent surveys on the reef show things aren’t looking good. In the northern region it is thought that up to 50 percent of the reef is now dead, and it is seemingly spread south.

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