The Oceans Are Becoming Too Hot for Coral, and Sooner than We Expected
Soon the oceans will be too warm to support thriving coral reefs. USFWS – Pacific Region/Flickr, CC BY
This week, scientists registered their concern that super-warm conditions are building to a point where corals are severely threatened across the tropical Indian, Pacific and Atlantic oceans. They did so after seeing corals lose colour across the three major ocean basins – a sign of a truly momentous global change.
This is only the third global bleaching event in recorded history.
Underwater heat waves
The situation has been worrying scientists like myself for many months. Over the past 12 months, the temperatures of the upper layers of the ocean have been running unseasonably warm. Underwater heatwaves have torn through these tropical regions over summer, and corals across large areas of reef have lost their colour as the algal partners (or symbionts) that provide much of the food for corals have left their tissues. Bereft, corals are beginning to starve, get diseased and die.
The “heatwaves” that are causing the problem are characterised by extremes that are 1-3 degrees C warmer than the long-term average for summer. It doesn’t seem like much but past experience has shown us that exposure to small increases in temperatures for a couple of months is enough to kill corals in great numbers.
In the first global mass bleaching event in 1998, regions such as Okinawa, Palau and north-west Australia lost up to 90% of their corals as temperatures soared.
By the end of 1998 up to 16% of the corals on the world’s tropical reefs had died.
The key concern here is that corals are not an inconsequential part of the biology of the ocean. While geographically insignificant (less than 0.1% of the ocean), coral reefs punch well above their weight in terms of their importance to the ecology of the ocean and to humans.
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