[Coral-List] Evidence that ocean warming has caused most Caribbean coral loss
riskmj at mcmaster.ca
Tue Apr 25 20:51:04 EDT 2017
Hello John, colleagues.
I hesitate to respond, because all too often these exchanges degenerate into
two guys talking past each other. Nonetheless, I wish to make myself clear,
and to clear up some items.
When I referred to reefs declining before significant warming, I was taking
temperature data from your post. I am well aware of the progress of warming
of the Caribbean. You seem to infer that I have failed to post references to
land-based stress going back to the 70's-but if you are publishing on the
Caribbean, you know this literature as well as I do-or you should. To take
but one example: Phil Dustan's work clearly shows decline well under way by
the early 1970's-I encourage all to look at the depressing time-lapse photos
he posts at https://biospherefoundation.org/project/coral-reef-change/
He attributes the decline to land-based pollution. In followup work in
Florida, Craig Downs found that bleaching was accelerated by oxidative
stress, probably from pesticides:
In short, decline was well under way by the early 70's-but you knew this.
One of the advantages of retrospective analyses of corals and gorgonians is
that it allows us to generate baseline-ish data where none had existed
before. In the case of the Florida Keys, Ward-Paige et al (2005: MEPS 296:
155-163) relate that decline to changes in water quality. In their Fig. 5,
the difference between 15N ratios from "clean" and "dirty" sites converge
back in the early 70's. By the present, they differ by 2per mille (a value I
have suggested elsewhere should trigger enforcement involvement). In short,
the WQ started going bad in the 70's. Similarly, we were able to trace the
decline in WQ in the Red sea off Jeddah since 1950, during which the reefs
declined (Risk et al., 2009: MEPS 397: 219-226).
Saying we have not lost any reefs yet, just corals, is playing with
semantics. More than a decade ago, I was asked to evaluate the reef
monitoring programs in the Florida Keys. I had been away, mostly in
Asia...and was horrified by what I learned. Coral had declined from 45%
cover to <4% (and it's lower, now). In my report, I referred to this as a
"regional mass extinction." This wording, although correct, was removed in
the final copy. A substrate with a scattering of corals is not a reef. In
fact (zowie, huge other subject!) there have been several recent papers
pointing out that most modern reefs are in a negative balance, due to the
nutrient-driven acceleration of bioerosion.
You miss my point, about running experiments about survival rates of
unstressed reefs. The examples you cite are not convincing. We have known
for decades that terrestrial influence can extend >100km offshore (Sammarco
et al., 1999: MEPS 180: 131-138, and earlier papers). I suggest another
thought experiment: had terrestrial stresses been removed from the Florida
Keys when Dustan first sounded the alarm, those reefs would now be healthier
than those of Cuba, much closer to the warming centre. I can't say much
about this Cuban MS I have, because it's under review, but they make it
clear that yes, those reefs are generally in better nick than the Caribbean
in general-except near sources of land-based pollution.
There are a lot of very clever people in this field. Speaking very
personally, I would like to see some of the smart biologists who spend their
time mining others' papers for trends move out of their comfort zones and
get into the chemical and geological aspects of this field. There's not a
lot of time left.
From: Bruno, John [jbruno at unc.edu]
Sent: April 25, 2017 8:50 AM
To: Risk, Michael
Cc: coral-list at coral.aoml.noaa.gov
Subject: Re: [Coral-List] Evidence that ocean warming has caused most
Caribbean coral loss
Dear Mike, thank you for your ongoing interest in this topic and my post.
"the Caribbean had already lost more than half its reefs before water
temperatures had increased by more than a fraction of a degreeâ
This is a common misconception from folks unaware that global warming began
many decades ago. Please have a look at the NOAA data plotted in this figure
4/ Or the graphics in Kuffner et al 2014 below it. These data should sort
you out. The Caribbean had clearly warmed significantly by the time mean
coral cover had been roughly halved (around the mid-1980s). Also, we
havenât lost any reefs yet, what weâve lost is coral cover (and fish
Ivâe dove near Havana and I agree - its a mess and was probably locally
impacted. And I donât understand the logic in arguing managers should give
up because climate change has had significant impacts on corals. Iâve said
it a million times: local impacts need to be mitigated. We all agree on
that. I think youâre underestimating managers and local conservation
capacity. (All the managers I know acknowledge climate change but arenât
giving up). As the Ocean Optimism symposium highlighted over the weekend,
local successes are realistic and very much meaningful and worthwhile.
"and there is overwhelming evidence of land-based stress going back to the
You have been promising this list-serv these references for years now. If
you ever find them, please do share with us if you have the time.
"how well could coral reefs survive ocean warming if they were not already
stressed by [local] human impacts?â
That experiment has been run dozens of times. On the northern GBR, on Scott
Reef, off Southern Cuba or in the Bahamas, across the central Pacific, etc.
The answer is not well at all..
The reason is that local impacts do not appear to act synergistically with
ocean warming. As Cote and Darling suggested
0438), the interaction appears to be antagonistic, not synergistic. Either
that or the impact of warming is so much stronger that it swamps the local
and synergistic signals. Also see Darling et al
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