Filed under: 2016, climate change, coral reefs, Hot Earth Dreams, Oceania | Tags: climate change, coral reefs, Great Barrier Reef Bleaching 2016, Mass Extinction
Another post, in part to remind myself that I’ll need to update the chapter on reefs in Hot Earth Dreams. The bad news of March, at least in my opinion (aside from all the rain that didn’t fall on California) was that the bleaching of the northern section of the Great Barrier reef (as mentioned by, among many others, National Geographic, DW, Slate, CNN, and The University of Queensland. Personally I like the last one the best, but tastes differ).
What’s going on, to be brief and oversimplify, is that coral have a temperature range, and the Coral Sea, or at least parts of it, are exceeding that range with this year’s El Niño. By itself it’s a tragedy, and it’s one that’s going to leave a mark that’s bigger than you might think.
I don’t consider myself an expert on the study of mass extinction, just a student of others’ work. What I’ve noticed, reading the papers, is some fairly fundamental things they teach in introductory paleontology (and yes, I’ve seen this in an introductory textbook). The bad news is that life forms don’t all fossilize equally, nor do all ecosystems. You probably know this already, but it’s worth repeating what may be obvious to you. Fossils tend to accumulate in places where sediments accumulate: lakes, bogs, marshes, swamps, occasionally rivers, sometimes deserts, and most of all, oceans. Places like mountain tops and islands don’t produce as many fossils as one might hope, nor do places like rain forests, dry forests, and so on. Most of the ecosystems I’ve worked in (chaparral and oak savannas) won’t leave much of a fossil trace beyond the oak pollen, unless things get weird.
Getting back to the mass extinction boffins, what I’ve noticed, reading some of their papers, is that they tend to focus on evidence from places that accumulate fossil really, really well. This makes perfect sense, because it minimizes the amount of randomness that messes with their already tenuous fossil records. Some of the best papers on mass extinctions focus on things like clams and, yes, coral reef fossils.
Coral reefs tend to leave behind really, really good fossils. Not everything that lives in them fossilizes, but they’re so huge, and the corals are, well, rock, so they get represented disproportionately in the fossil record and in mass extinction studies. I’ll probably get slapped around if any serious paleontologist reads this, but my sarcastic impression is that at least some studies of mass extinctions are basically studies of how reefs disappear and reappear in the fossil record, with a side of clam shells and a few dinosaur bones thrown in to diversify the sample.
This is the gravely quiet subtext to the Great Barrier Reef tragedy. If we don’t get this stopped by dealing with climate change like 50 years ago, we will see more and more killer El Niños hit the reefs. At worst, the Coral Sea could heat permanently to El Niño temperatures, the water too hot to support corals at all (this from Veron’s excellent A Reef In Time). If this happens (I’m whistling past the graveyard by not saying when), whatever’s left of the dead Barrier Reef will begin its transformation into the next fossil record of a so-called “reef gap,” a time when the oceans were too acidic/anoxic/hot to support coral reefs. These are the classic sign of extinction events, although they’ve happened more often than the five big mass extinctions.
So here’s the thing about the 2016 bleaching event: we may be seeing the beginning of what future paleontologists will label as the Sixth Mass Extinction. It’s not set in stone yet (literally), but absent heroic measures starting this Friday when world leaders sign on (or don’t) to the COP21 Agreement, we’re heading into studies of how reef gaps form, as the fossil record formation portion of the Sixth Mass Extinction heats up to working temperature.
Just remember that reefs are home to something like 25 percent of the world’s species. While the loss of reefs isn’t the loss of all those species–some, like humans, live outside reefs–but it’s the loss of most. Reefs are up there in diversity terms with tropical rainforests, which leave behind rather poorer fossil records. They’re also rather richer in high level diversity (32 of 24 animal phyla are found on reefs, compared with 9 animal phyla known from rainforests). If our coral reefs disappear, that’s an extinction event in itself, whatever else happens in the rest of the world. Given what’s happened in past reef gaps, if coral reefs disappear, they won’t return for something like five million years. That absence is a sad legacy to leave, don’t you think?
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