[Coral-List] Coral on the Great Barrier Reef was 'cooked' during 2016 marine heatwave. REALLY? REALLY? REALLY? #2

Fri May 4 10:26:02 EDT 2018

Scott,

Our Hughes et al. Nature paper from March 2017 analyzed for proximity to
nutrient sources and saw no significant impact on bleaching.  While the
bleaching (Hughes et al. March 2017 Nature), and our mortality paper
(Hughes et al. April 2018 Nature) both indicate that bleaching and
mortality were more severe than expected for the level of heat stress in
the Northern and Far Northern GBR, this is not unusual for reefs that have
not experienced prior heat stress. Bleaching patterns in the Central GBR in
2016 and 2017 were consistent with our usual heat stress thresholds used in
Alert Levels 1 & 2.

I fully agree that nutrients can have an impact on bleaching and mortality
in some corals. Of course, they can be an even bigger factor in recovery.
However, if nutrients were a driving factor in the 2016 and 2017 GBR
bleaching, we would have expected higher bleaching closer to nutrient
sources and lower away from them -- such as the Far North. Instead, we saw
the opposite.

We would be glad to work with you on a more in-depth analysis of the
potential interactions of heat stress and nutrients during these bleaching
events if you have hypotheses you think could be tested using field data on
bleaching and nutrients along with our data on heat stress.

Cheers,
Mark

On Fri, Apr 27, 2018 at 1:09 PM, Scott Wooldridge <swooldri23 at gmail.com>
wrote:

> Hi John,
>
> Many thanks for your response. Sorry for my slow response. Seems i have a
> email feed for corallist that is much slower than some.
>
> First, can i just make very clear that I dont question in the slightest
> that man-induced (rising atmospheric pCO2) warming is the driver of modern
> mass coral bleaching events on the GBR and elsewhere. I have no hidden
> agendas, and strongly support the hope of most scientists that global
> temperature rises can be kept below 1.5-2.0 degrees celsius across the
> coming century through aggressive global CO2 mitigation strategies
> (principally a transition away from fossil fuel intensive economies).
>
> My thesis is that warming ocean temperatures (and rising pCO2) have served
> to make previously acceptable levels of nutrient-enrichment (from
> terrestrial runoff and/or natural upwelling) now unacceptable and
> destabilising for the coral-algae symbiosis. In this way, bleaching
> sensitivity (per unit thermal stress) can be expected (and has been
> observed by many authors) to increase in response to variable gradients of
> nutrient enrichment. The driver (triggering event) of the event is the well
> reported combination of anomalous SST and irradiance, but the sensitivity
> of the bleaching (and possible mortality) response is co-dependent on
> nutrient enrichment levels.
>
> To see the above description represented visually, see my Fig. 2 in:
>
> https://www.researchgate.net/publication/299939163_Excess_
> seawater_nutrients_enlarged_algal_symbiont_densities_and_
> bleaching_sensitive_reef_locations_2_A_regional-scale_
> predictive_model_for_the_Great_Barrier_Reef_Australia
>
> n.b. my analysis for the GBR also highlights that the thermal history of a
> site interacts with the nutrient status of the site in determining
> bleaching sensitivity/resistance. All this is well described in the above..
>
>
> I hope that is really all really clear.
>
> In terms of the 2015/16 bleaching and SSTs on the GBR i think it would be
> great to hear from Mark Eakin (NOAA). I consider Mark a good friend and
> have the greatest of respect for the NOAA coral bleaching products. No one
> should know better than Mark whether the degree of bleaching and mortality
> in the far northern GBR in 2015/16 was expected given the observed level of
> heating, and other precedent events such as 2008/09.
>
> Any chance you could give a little summary Mark? And your take on whether
> other factors (beyond heat stress alone) might be at play? As scientists,
> do you believe we should be looking at other factors beyond SST alone
>
>
> scott
>
> https://www.researchgate.net/profile/Scott_Wooldridge
>
>
>
>
>
>
> > Dear Scott,
> >
> > Thank you for sharing your idea about the real cause of mass bleaching
> on the GBR. As your’e probably aware http://www.co2science.org (a fossil
> fuel industry funded website) has been pushing this idea for a while.
> Arguing that pollution, fishing, seaweed etc are the real reason corals are
> bleaching and dying. Despite that, I’m open to the hypothesis. But based on
> past experiences on the coral-list, it seems to me the more vocal and
> confident people are about the role of nutrients, the less data / science
> they have in support of their explanations.
> >
> > In your case, what makes you think thermal stress was low or lower in
> 2016? You claimed DHW was only 3-4, but that contradicts the evidence:
> Hughes et al 2081 report that across the northern GBR, DHW was ~ 8-14
> preceding the event and that severe bleaching occurred on reefs with DHW
> values of ~6-10. The NOAA Coral Reef Watch portal indicates the same:
> https://coralreefwatch.noaa.gov/vs/gauges/gbr_far_northern.php
> >
> > Moreover, 2016 was the warmest year on earth in recorded history (NOAA
> ranks 2009 as the 8th warmest). The ABM confirms this for the GBR: 2016 was
> the warmest ever, and far warmer than 2009: https://www.dropbox.com/
> s/2q9uk1xewedtp58/Feb-2016-sea-surface-temperature.png?dl=0
> >
> > So your’e wrong about the thermal stress. And you don’t provide any
> values on nutrient concentration. While chlorophyll conc. is often
> generally indicative of nutrient conc., the relationship is very messy and
> chlorophyll can’t be used to make precise predictions about DIN. For one,
> other factors influence chlorophyll, including temperature, predation,
> other nutrients, etc. And to make such a comparison, you’d have to control
> for other factors demonstrated to have strong effects on community thermal
> sensitivity, eg coral composition and cover.
> >
> > Again I’m open to the idea and anything we can do to meaningfully reduce
> bleaching. But wouldn’t you think that if local N pollution increased
> bleaching sensitivity by ~2C (Wooldridge<https://www.resear
> chgate.net/profile/Scott_Wooldridge> 2009) we’d be able to detect that in
> nature? Why would reefs in pristine locations ever bleach? We've seen so
> many highly isolated, “pristine” reefs bleach w mass coral mortality over
> the last decade (not only the N GBR), I’ve become suspicious of claims
> about local drivers of bleaching sensitivity. Moreover, we’re losing coral
> as rapidly on isolated atolls as we are on reefs adjacent to inhabited,
> industrialized coastlines (https://www.nature.com/articles/srep29778).
> >
> > Regardless, I appreciate you sharing your passion and ideas. But maybe
> next time come armed with some evidence.
> >
> >
> > John Bruno
> > Professor, Dept of Biology
> > UNC Chapel Hill
> > www.johnfbruno.com<http://www.johnfbruno <http://www.johnfbruno.com/>
>

-- 

C. Mark Eakin, Ph.D.
Coordinator, NOAA Coral Reef Watch
National Oceanic and Atmospheric Administration
Center for Satellite Applications and Research
Satellite Oceanography & Climate Division
e-mail: mark.eakin at noaa.gov
URL: coralreefwatch.noaa.gov
Twitter: @CoralReefWatch <https://twitter.com/coralreefwatch> FB: Coral
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"A world without coral reefs is unimaginable."
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