Not too long ago I shared with you a story on how ocean acidification (as I explained then in more detail, driven by increased atmospheric CO2 content) not only hinders coral reef growth but is also dissolving them at an alarming pace. Sadly, ocean acidification is only one battlefront. In a new communication published in the journal Nature, scientists report on how the warming of the oceans is having dire consequences for the Great Barrier Reef, off the coast of Queensland, Australia.
Ocean warming is known to be one of the main causes behind coral bleaching, an event characterized by the ejection of symbiotic brown and green algae, such as zooxanthella or zoochlorella, from the corals, returning them to a white or "bleached" state. These algae provide the corals not just with their colour but also with food and, in return, living inside the corals allows the algae to have increased metabolic production, probably thanks to the corals providing CO2, certain nutrients and a more elevated position to receive sunlight.
But this is a precarious symbiotic relationship. When under stress, corals eject their algae, and the problem now is that global warming has made stressful oceanic heatwaves much more frequent and long-lasting. Prof Terry P. Hughes, one of the team leaders behind the new report and director of Australia's ARC Centre of Excellence for Coral Reef Studies, explains that after bleaching from a heatwave “[corals] can either survive and regain their colour slowly as the temperature drops, or they can die. Averaged across the whole Great Barrier Reef, we lost 30% of the corals in the nine-month period between March and November 2016.”
To the surprise of the researchers, these deaths occurred much quicker than expected. It was thought that death would come slowly after bleaching as the corals begin to starve, but the new study provides evidence that the increased heat is killing corals directly. Prof Andrew Baird, one of the report's co-authors, further explains that coral reefs are suffering a quick degradation with only "a few tough species" surviving, while Prof Hughes is looking at the glass half-full: "[This] still leaves a billion or so corals alive, and on average, they are tougher than the ones that died. We need to focus urgently on [...] helping these survivors to recover.” Of course, this hinges on world governments limiting the global average temperature rise to a 1.5°C to 2°C increase on pre-industrial levels, a goalpost not likely to be met.
Read more here:
"Great Barrier Reef: 30% of coral died in 'catastrophic' 2016 heatwave" at The Guardian
Read the original scientific communication here [PAYWALL]:
"Global warming transforms coral reef assemblages" at Nature
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I guess it is hard to know if 1.5 to 2 degrees will result in the remaining coral surviving - given the huge impact the warming has already had I presume we are going to see more corals die off as temperatures continue to rise and ocean heatwaves become more intense.
I guess it is hard to know if 1.5 to 2 degrees will result in the remaining coral surviving - given the huge impact the warming has already had I presume we are going to see more corals die off as temperatures continue to rise and ocean heatwaves become more intense.