The supposedly already-degraded state of coral reef ecosystems is sometimes claimed to be a reason why anthropogenic global warming will have a major impact on the reefs, i.e. they are already close to extinction and can easily be tipped over the edge.
A recent paper** by Peter Ridd challenges the methodology used to conclude that the outer and inner Great Barrier Reef (GBR) are already 28% and 36% respectively, down the path towards ecological extinction.
I’ve uploaded the full paper, with permission from the author, here: http://jennifermarohasy.com/data/Ridd_Energy%20n%20Environment.pdf
** A CRITIQUE OF A METHOD TO DETERMINE LONG-TERM DECLINE OF CORAL REEF ECOSYSTEMS
by Peter V. Ridd. Reprinted from ENERGY & ENVIRONMENT, VOLUME 18 No. 6 2007
I’ve seen a German documentary about some scientist researching coral bleaching. She was shown collecting the pieces/branches of live coral on the sea bottom, that were detached during a storm, then fixing them by plastic bands to the bleached parts. She declared, that the corals then started to spread onto the bleached reef. If this is indeed so, then the bleaching conditions can’t be permanent, can they?
I think that attaching broken pieces of coral to bleached coral with the expectation that “the corals then started to spread onto the bleached reef” is a bit wrong and something of a stunt.
You are right though in concluding that bleaching isn’t necessarily permanent.
What I expect the scientist intended was to encourage re-population of zooxanthellae, the symbiotic single-cell algae that corals receive some of their food from.
It is this algae that give corals their colour, and it is the loss / decrease of this algae that causes bleaching. The coral (the filter feeder polyp) can survive for several weeks (even months) without it. If the original zooxanthellae does not recover, all is not lost. A different species of zooxanthellae (better suited to the changed conditions) may establish itself, and the coral may indeed change colour…
Ian Mott says
It should also be noted that the corals are not all at uniform depth so the upper parts may bleach while the lower parts remain as they were. The remaining algae are then able to start to recolonise the bleached parts the moment the extreme conditions pass. And any suggestion that the next coral sporn would be unable to deliver a partial supply to recolonise the damaged parts is plain ludicrous.
And as we know, all it takes to end those extreme conditions is a stiff breaze.