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

Scott Wooldridge swooldri23 at gmail.com
Mon May 7 18:42:34 EDT 2018


 Hi CoralListers,

Just a couple of quick points to end my contributions to this discussion -
i hope it has been useful to you.

 As i have previously mentioned. The far north was SEVERELY tested by heat
stress in 2008/09, possibly even more so than in 2016, yet there was NO
bleaching.

https://www.researchgate.net/publication/324644910_
Comparison_of_heat_stress_in_the_northern_GBR_for_201516_and_200809

For the 2016 event a MORTALITY trigger threshold of 3-4 DHW was recorded
(as per Hughes et al. 2018 abstract, and results). A DHW of 3-4 is normally
only a 'watch level" for mild bleaching - normally far away from expecting
any mortality, which is usually >10 DHW.

As for the analysis in the Hughes et al. 2017 paper looking for possible
linkages to water quality, it was ineffectual and misleading, and should
never have passed through peer review. Everyone with a knowledge of this
field knows that you CANNOT use remote-sensing (seawiffs, MODIS) wq
estimates for shallow-water reefs, particular reefs on continental shelves
that have complex optical properties due to turbidity or other particulate
organic matter. The algorithms are are only valid for open oceanic waters.
Whilst working at AIMS i spent >10 years putting together a valid nutrient
(DIN) enrichment spatial dataset for the GBR based on field measurements.
It shares very little (to no) relation to what the remotely sensed data
indicates (see linked appendix A). How can it, the sensors can see the
bottom to at least 30-40m (and classify these ares as high nutrients), and
also record high nutrients if wind driven resuspension of sediment
turbidity or POM is the cause. After working collaboratively with Jon
Brodie (the guru of GBR water quality) since 2003, even in our 2016 paper
we were not confident to specify the water quality in the far north (see
our discussion, and reasons for omitting the far north from our analysis)

https://www.researchgate.net/publication/309375867_Supplementary_Appendix_A

And lets say, that miraculously somehow the remotely sensed water quality
was correct. Even in this case, as i have alluded, because the whole far
north is recorded as high nutrients (due to broad-scale upwelling being the
cause), then the 2017 data would have no power to discriminate wq as an
effect in any case. For example, if the majority of the data is classified
as elevated nutrients (at the reef scale), there is not enough variance in
the dataset to discriminate WQ as a key variable. WQ will in this case be
shown as a poor predictive variable. All the variance will be attributed to
heat stress. The fact that fundamental wq thresholds have been triggered to
allow the direct sensitivity to variations in heat stress is not captured.
It is for this same reason that most small scale studies report wq as a non
factor, not enough variance in the data. This is why the 1998 and 2002
bleaching events on the GBR were so valuable. they had a large range of wq
x heat stress combinations. Perhaps all this may not make much sense to
non-statisticans, but trust me when i say that the conclusions reached by
Hughes et al 2017 are not valid theoretically or statistically.

If you think i am biased in this appraisal, then feel free to ask Jon
Brodie who knows the water quality story on the GBR better than any man
alive.

Please can everyone be very clear. I have absolutely NO problem  with the
NOAA heat stress maps. I think they are GREAT, and have used them
successfully in many publications. BUT in every case on the large scales of
the GBR, i have never been able to use them to predict bleaching (yes/no)
with an accuracy of >60%. Remember 50% is a random (flip or a coin) guess,
and 55% is typically what you get if you guess that all the reefs bleached
because you know it was a particularly HOT year. That leaves a lot of
unexplained variance (~40%) in the NOAA products as i show in Fig.1 for the
1998/2002 events on the GBR:

https://www.researchgate.net/publication/308746844_Excess_
seawater_nutrients_enlarged_algal_symbiont_densities_and_
bleaching_sensitive_reef_locations_2_A_regional-scale_
predictive_model_for_the_Great_Barrier_Reef_Australia

For the uninitiated,the BEST use of the NOAA heat stress maps is for
predicting reefs that are unlikely to have bleached because of low SST
(~75-80%). Predicting bleaching due to heat stress falls to ~50-55%.
Leading to the ~60% predictive accuracy. (this is based on the 1998/2002
events on the GBR). We can do much better than that when we included WQ and
solar radiation impacts (see the above paper for details).


And so i will leave it there. Feel free to make up your own minds.

For me, I am not at all convinced that heat stress alone was the cause of
the severe bleaching/mortality response seen in the far northern GBR in
2016. I am definitely sure that they were not 'cooked alive' given the DHWs
reported at the reefs.


scott

https://www.researchgate.net/profile/Scott_Wooldridge






On Sat, May 5, 2018 at 12:26 AM, Mark Eakin - NOAA Federal <
mark.eakin at noaa.gov> wrote:

> 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_se
>> awater_nutrients_enlarged_algal_symbiont_densities_and_bleac
>> hing_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
> Reef Watch <https://www.facebook.com/coralreefwatch/>
>
> NOAA Center for Weather and Climate Prediction (NCWCP)
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> Office: (301) 683-3320     Fax: (301) 683-3301
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>
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> Dr. Jane Lubchenco, March 25 2010
>


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