[Coral-List] Has the death of the Great Barrier Reef been greatly, exaggerated??
Douglas Fenner
douglasfennertassi at gmail.com
Fri Oct 28 00:54:45 EDT 2016
Gene,
This is once again long, be forewarned.
Abstract: I think Gene is right about the GBR (Great Barrier Reef) and
exposure to air killing life on the reef at low sea level stands. We often
say that a reef is "dead", but while a coral reef ecosystem can die, a reef
is a geological structure, and was not itself ever alive, and can continue
to exist long after the corals are dead and long after it has been out of
water. Further, the damage from the recent mortality event will not be
forever. The GBR coral reef ecosystem may well not recover in our
lifetimes or even several generations (though it might recover much coral
cover in a few decades or even less), but saying it will be damaged forever
is not realistic. It may well not recover from this damage before
additional damaging mass bleaching events hit it and further damage it.
Sooner or later, that appears to be the fate of all coral reefs, unless
action is taken. Cold fronts didn't cause this damage, nor did toxic
sunscreens (and Gene didn't say they did). Hot water from El Nino on top
of global warming did it.
Gene,
Thank you for this perspective! Indeed, this is my understanding of
the outline of GBR geological history. At low sea level stands, such as
the one that was lowest 22,000 years ago, all of the present world's coral
reef ecosystems were out in the air, and all corals that had been on them
were dead (as well as everything else that was living on and in them,
replaced by terrestrial plants and animals). The coral species survived,
living lower down on the slopes in the sea water. Then when the ocean
rose, the corals settled higher and higher on the slope as it was covered
with water. There are a few presently raised reefs around the world that
illustrate what reefs out of water looked like, including several islands
in Tonga and several more in the Marianas, and the tiny Pacific islands of
Nauru and Niue. In the parlance that some people use, when a reef is
exposed to air for thousands of years, it is "dead." Well, a coral reef
ecosystem in the air is certainly dead, although the reef geological
structure is still there, at least for thousands or millions of years until
rainwater dissolves it (partly dissolved limestone is called "karst" I
believe; rainwater is a weak acid due to CO2 from the air dissolving in
it). And this brings up the statement that a few have made that "the reef
will never recover." As some used to say, "never" is a long time. "Never
in our lifetimes" or "never in a management time frame" could well be true,
but "never" is highly unlikely. Coral reef ecosystems have recovered
completely from mortality of all life on them from exposure to air, when
they were resubmerged for enough time (Gene pointed out that the GBR has
been exposed to air off and on many times, killing the reef organisms each
time, this implies that the organisms had to have recovered each time as
well or they couldn't be killed off the next time). Coral Reef ecosystems
can also reconstitute complex ecosystems, as was demonstrated by Pandolfi
on the Huon Penninsula in Papua New Guinea, where land has been rising for
hundreds of thousands of years, and there is a stair step of reefs up the
side of the hill above the present water level. Each reef up on the
hillside above water has a coral composition like that of the presently
living coral reef ecosystem in the water below it. The complex reef
ecosystem has been reconstituted over and over. The caveat is that it
takes time. There are reports of reefs recovering coral cover from mass
coral mortality from hurricanes or mass coral bleaching in a decade or two,
or less. Other reefs have not recovered so far, such as those that haven't
recovered in the Indian Ocean after the 1998 bleaching. And recovering
coral cover is not the same as recovering the coral species composition, or
colony size distribution, or all functions and processes, or recovering the
largest and oldest coral colonies (which can range up to over 750 years
old- there is a core from a massive Porites colony in the North Queensland
(Australia) Museum that has about 750 annual growth rings, and that isn't
the largest coral known). So full recovery can take well over a human
lifetime, if not a few thousand years. Blink of an eye in geological time,
but "near forever" in the time frame of human lives and management. Of
course, continuing warming will cause bleaching mortality events to occur
more and more often, with not enough time between them for recovery.
Thousands or hundreds of thousands of years from now, the CO2 in the
atmosphere will have been absorbed probably by rock weathering,
temperatures will come down, and corals will recover except for any species
that may have gone extinct. If some do go extinct, within a few million
years new species of corals will have evolved. Only one small problem,
that's "almost forever" in human terms.
In common parlance, most of us (I include myself) refer to "the reefs"
when we are really talking about coral reef ecosystems, the living
ecosystem. But taken literally, someone can interpret what we're saying as
meaning the geological coral reefs (which is what a "reef" is, other than a
rocky reef in a temperate zone), which are calcium carbonate, can die or
disappear. While a geological reef houses lots of life, the reef itself
does not die from bleaching or exposure to air, and it doesn't cease to
exist on our time scale, only in geological time scales, usually in
thousands of years or more, can be in the millions of years (there are
fossil coral reefs on land that are many millions of years old, they still
exist). We would do well to lift our game and start making a clear
distinction in what we say and write between living coral reef ecosystems
and reef geological structures (though obviously the two are related, the
geological structure is the habitat of the living ecosystem, and the living
ecosystem constructs that geological structure).
Granted, journalists are not going to publish a full explanation in a
newspaper, they don't have the space. It is not easy to parse every word
so carefully when talking to the press as to have every last word
technically correct. But we need to try, anything that could be
interpreted as an exaggeration could be used against us.
Cold fronts certainly can kill corals. Lots of things can. But while
Florida is subtropical and just south of a large temperate continent, so it
gets nasty cold fronts coming off the continent in the winter sometimes,
the GBR is in northern Australia, where (in my limited experience of 6
years living there) there seem to be no cold fronts. Tasmania, down off
the south coast of Australia certainly gets highs, lows, and cold fronts
coming through, Queensland doesn't, no rotating highs and lows moving along
or cold or warm fronts, it is too tropical, it mostly has a stationary
"trough" of low pressure sitting over it (it does get cyclones, though).
All the evidence is that this mortality event on the GBR was not caused by
cold, rather the opposite, and there is abundant evidence that the water
temperatures on the GBR have been rising for a long time (the Guardian
article has a very clear graph of temperatures rising on the GBR). Neither
was it caused by toxic sunscreens. In fact I don't know of any strong
evidence of sunscreens causing coral mortality over one square kilometer,
let alone the many thousands of square kilometers where they were killed on
the GBR this year or the 16% of the world's corals estimated killed by the
1998 El Nino hot water. There are virtually no people up at the northern
end of the GBR or putting sunscreens in the water there. (Gene didn't say
they did.) Correct me if I'm wrong, but haven't most of the largest coral
mortality events in the world in the last few decades been caused by high
water temperatures (maybe the crown-of-thorns outbreaks on the GBR and in
Japan are in the same league, but neither cold fronts nor sunscreens are)?
Isn't there strong evidence that the world as a whole is warming?? Isn't
there a strong correlation between high sea surface temperatures and
bleaching, such that NOAA Coral Reef Watch can predict accurately the time
and location of coming bleaching events?? Should we just stand by and let
it happen, and use as much fossil fuel as ever and cash our dividend checks
from fossil fuel companies?? If so, then the original obituary will likely
prove true by 2100 if not sooner, perhaps much sooner. RIP, coral reef
ecosystems. (Small cost to pay to protect giant profits, right? The
people who will pay most dearly for the loss of coral reef ecosystem
services are poor people along the coasts of many tropical countries, not
the relatively rich Americans that have burned by far the most fossil
fuels.) But there is some hope for corals, a recently signed international
agreement to stop using HFC (hydrofluorocarbon) coolants is predicted to
reduce the rise in world temperatures by as much as 0.5 C, that's huge when
you're trying to limit warming to just 2 C or better yet 1.5 C.
Cheers, Doug
Guardian article
The Great Barrier Reef: a catastrophe laid bare
https://www.theguardian.com/environment/2016/jun/07/the-grea
t-barrier-reef-a-catastrophe-laid-bare
Countries reach landmark deal to limit global warming
http://fortune.com/2016/10/16/global-warming-hfcs-deal/
On Wed, Oct 26, 2016 at 5:23 AM, Eugene Shinn <eugeneshinn at mail.usf.edu>
wrote:
> I recall that coring and seismic profiling showed the linear great
> barrier reef (like the outer reef in the Florida Keys) is quite thin
> (only a few meters) and underlain is by terrigenous sediment. Like the
> Florida reef tract it has only been submerged for between 6 and 7
> thousand years (not 25 million years as the article states). The barrier
> reefs has been in and out of water many times during the past 25 million
> years and suffered mortality each time it was left high and dry. The
> present reef was dry land between 6 and 7 thousand years ago. The
> thickest coral accumulations are the patch reefs (composed of corals and
> Halimeda) that lie in the deeper lagonal area landward of the great
> barrier reef. Same is true in the Florida Keys. Our USGS Fisher Island
> group presented a paper titled /Autopsy of a Dead Reef/ at the annual
> SEPM meeting in the 1970s. It was about Hens and Chickens reef in the
> Keys which had suffered near total mortality caused by a cold front
> during the winter of 1969-70. The time of death was clearly preserved in
> annual growth bands of both living and dead coral heads. One may wonder
> if similar periodic paleo cold fronts kept the linear outer reef in
> check during the previous 6,000 years. Gene
>
> --
>
>
> No Rocks, No Water, No Ecosystem (EAS)
> ------------------------------------ -----------------------------------
> E. A. Shinn, Courtesy Professor
> University of South Florida
> College of Marine Science Room 221A
> 140 Seventh Avenue South
> St. Petersburg, FL 33701
> <eugeneshinn at mail.usf.edu>
> Tel 727 553-1158
> ---------------------------------- -----------------------------------
>
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--
Douglas Fenner
Contractor for NOAA NMFS, and consultant
"have regulator, will travel"
PO Box 7390
Pago Pago, American Samoa 96799 USA
phone 1 684 622-7084
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