[Coral-List] Thoughts on coral decline and the future.
Risk, Michael
riskmj at mcmaster.ca
Mon May 8 11:49:03 EDT 2017
It is raining, firewood stacking is on hold, so I thought I would add some
more to this mix. This has been a generally excellent exchange, with some
important and insightful comments from smart people. I think I am summing-up
here, but I may just be rambling.
First of all: I learned early on not to waste time in exchanges with those
who resort to insults and invective. John Bruno, telling your colleagues
that they are “denying reality” and “peddling nonsense” is outside the
bounds of professional debate. I suggest you lift your game.
At the centre of this debate is what has happened to our ecosystem, and what
we can do about it. John has been very forceful in his statements that the
Caribbean decline has been driven by temperature changes, whereas I think
that viewpoint is myopic. Using data in the references John has been kind
enough to provide, we could estimate that from say 1960 to 1980 the
Caribbean warmed less than 0.5°C, during which we lost about half the corals
in the Caribbean-and those corals were still under their thermal limit. John
accuses me of pandering to the deniers, a comment which would be annoying
were it not so amusing, but I hope WUWT doesn’t get hold of his stuff. We
could be treated to postings ridiculing us along the lines of “scientist
says all Caribbean corals already killed by half a degree.”
I spent much of my professional career working in the developing world at
the sharp end of “coral reef decline”, where that means your kids might not
eat. It seems to me that focusing on future developments and ignoring local
stresses is a viewpoint driven by white Western privilege. If you don’t
really care what happens out there to off-white people, it’s much easier to
arm-wave about the future.
John maintains that reefs far from habitation are not “healthier” than reefs
close to shore. This is obviously incorrect for the general planet, but
there have been reports of isolated reefs suffering damage (the less said
about Bruno and Valdivia the better, in my opinion). I think we should
consider these critically, for several reasons. First of all, it may no
longer be possible to consider ANY reef as being isolated from human
impacts. Twenty (argh! Thirty!) years ago, our crude techniques were able to
trace terrestrial influence >100km offshore on the GBR. Secondly, we may
need to look closely at the science, especially as some of the “inverted
biomass pyramids” should be re-examined (Ward-Paige et al., 2010, PLoS
ONE). A few years ago, I received a manuscript to review from one of these
“isolated” reefs. In the supplementary data, I discovered that between the 2
regions, Affected and Comparison, there was a difference in the ratios of
stable isotopes of nitrogen of 2 per mille (there was a small village
there). Oh goody, said I, there’s the answer-in a much older paper, I had
suggested that this level of difference indicated significant sewage stress
and should trigger enforcement. Nope. The authors forged ahead with their
conclusion, that it was all due to overfishing.
Tom Tomascik has pointed us to a volume which should be widely read in the
biological community. It contains many examples of reefs that were simply
obliterated by terrestrial stress, including his own description of the
disappearance of reefs offshore Jakarta. I think his paper comes as close to
poetry as science allows, but it is ineffably sad. “The unrivalled splendour
and wealth of forms” in 1928 of a reef that no longer exists…In that same
volume, Terry Scoffin (RIP) describes the decline of the iconic Bellairs
Reef on Barbados as due to eutrophication and sedimentation in the 80’s-and
of course Tom’s own papers on eutrophication and corals are classics.
I hope we can all agree that reefs are facing land-based stress AND global
change stress: one started when the first Neanderthal washed her face in the
Mediterranean, and the other when the first oil well was drilled at
Petrolia, Ontario. There is a large body of research supporting the
contention that land-based stress dominated until late in the 20^th century,
but global warming is gaining quickly in a race we would rather not watch.
We need to figure out what our responses should be, and perhaps for the
first time speak with one voice.
I was delighted to see the Earth scientists chime in, because knowledge of
that field seems to be notably lacking in many of our biological colleagues.
We need to learn from history. We are in the early phases of the
Anthropocene Transgression, and to prepare for the future we should study
the Holocene Transgression. Sea-level rise during the Holocene was not
gentle and steady, but likely proceeded through a series of “jokelhaups”, or
catastrophic meltwater releases. Ulf feels that some of the 35-meter rises
in sea level cited earlier could have come in one day! Water velocities
during meltwater drainage off Eastern North America transported boulders 2 m
in diameter out onto the continental shelf. Melting of Greenland will play
havoc with thermohaline circulation, as it did in the past. This is what’s
coming.
This may not be a “slow-moving” catastrophe after all. Human populations
will be displaced, perhaps suddenly, by unpredictable rises in sea level.
The time may come when society as a whole may not have the resources to save
coral reefs, because people come first. Triage in action. If we wish to
prepare for this, we should be listening to the Pleistocene geologists.
It is highly unlikely reefs will be able to adapt by colonizing
newly-flooded landmasses. Walter Adey has shown that, during the Holocene
Transgression, there was a lag time, generally on the order of 1000 years,
before corals colonized the new substrate. Presumably this was to allow time
for waves and currents to rework and clean the bottom. The water that will
flood the continents during the coming transgression will be much filthier
than the Holocene water. In addition, the landmass will be much more
difficult to colonize: all those condos, highways, abandoned Hummers…
It would be wonderful to study a reef that had survived through the Younger
Dryas, but as Hal has pointed (hi, Hal), the critical outcrops are all under
water now. Of course, the oceans wouldn’t be as high now if it weren’t for
all those whales in them…
Hal has also been kind enough (?) to point out to us that many of the major
extinction events of the past have been driven by CO2 increases. The
terminal Permian event killed 80% of life on the planet. As this fact
becomes more generally absorbed and as the urgency grows, it may be possible
to reverse the warming trend. We have to hope so. Our job now will be to
protect those reefs that have a chance. We can’t do much about global
change, other than to contact our legislators and lead by example. What we
can do is try our utmost to reduce land-based sources. This bears repeating:
we as individuals can do relatively little about atmospheric CO2, but we CAN
as individuals do a lot to control land-based sources. Start with sunscreen.
All of our friends now avoid oxybenzone sunscreens. They also quiz
prospective resort destinations on how they treat their sewage. Most
maritime countries routinely monitor E. coli in their coastal waters. In
most Caribbean countries, the results are closely-guarded by the
State-because they fear tourist dollars would vanish if people learned how
filthy the waters were. We have immense influence, both as scientists and
consumers. Just imagine: what would Florida’s reefs be like now if, 20 years
ago, some of our reefy talking heads had said “I understand there is a
problem with sewage stress. Until you fix this, I am going to recommend
people go elsewhere for their holidays.” (I said this, but nobody listens to
me…) So now the Keys reefs, at the northern end of the Caribbean, are dead
as dodos, whereas Cuba, in the warmer centre of the Caribbean, still has
good reefs.
There are glimmers of hope. Paul Hawkens’ “Drawdown” outlines a reasonable
approach that could turn things around in a couple of decades. Tim
McClanahan’s new paper shows some (small) thermal adaptation in corals from
Kenya.
Many years ago (some Coastal Conference, early 80’s) I proposed we apply
“triage” to reefs. If we apply triage ruthlessly now, we can probably save
some reefs for the next half-century. If we keep the water clean, it may
even be possible to regenerate/restore some. We need to prioritize. One of
the critical factors will be our ability to characterise and quantify the
various threats/stresses, and this is an essential step in any reef-saving
exercise. Fortunately, our assessment “toolbox” now contains the necessary
techniques-from cellular diagnostics to trace element profiles. The
time-slice technique that has been used on gorgonians is especially powerful
in places with spotty baseline data. It can just as easily use bivalve
records or even scleractinians (although corals are procedurally more
difficult). It’s a useful technique that deserves wider usage. Trust me, it
isn’t hard-if it were hard, I could not do it. (If you want to know how, I
will walk you through off-line.)
And finally, as Gene is wont to do, he points us to cool stuff: Yates et al.
(2017). I strongly recommend listers read this, because it is a depressing
tour de force. Major lowering of the sea floor in studied areas (Florida, US
Virgin Is., Maui) such that erosion rates far outstrip potential
calcification rates. Authors are careful not to attribute causes-but we know
what’s probably doing this: nutrient-driven bioerosion. The fecal
bioindicator Cliona delitrix is all over the Florida bottom, with colonies
so large (it’s brick red) that they can be seen from a light plane.
Sorry for the long post. The devil makes work for idle hands when it rains.
Some ideas, some bad news, some good news. We need to hope, but we need to
remember that “hope is the pretty mask of fear” (Buddha). We need also to be
afraid-and we have reason to be.
Mike
More information about the Coral-List
mailing list