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

Tue May 8 20:16:58 EDT 2018

Hi Scott and coral-listers

Just to clarify the "water quality" situation in the far northern GBR in 2016. Scott is absolutely correct that you can't use MODIS etc on the GBR shelf to estimate chlorophyll - it doesn't work. We have only published technical reports about this and not papers but I can send anyone who is interested the pdf of the main report showing the problem. This is largely true in all Class II shallow waters where the algorithms don't work for chlorophyll. On the other hand the interpretation for TSS (turbidity, photic depth) does work to some extent but still with fairly large errors in shallow waters (less than 30m). Hence what was interpreted as a nutrient signal in the Hughes et al. 2017 paper Scott refers to, was actually a TSS/turbidity signal. The story then is probably that the presence of high turbidity does have a protective effect against bleaching (rather than the negative effects of nutrients) through reduction in the UV component of stress (and high intensity visible?).

The likelihood of high dissolved nutrient concentrations in the far northern GBR at the time is difficult to estimate. This is an area where there is both occasional upwelling as well as more regular tidal jets. The upwelling of course brings water with high nutrient concentrations from hundreds of metres depth. The tidal jets bring large loads of nutrients even if not such high concentrations. As noted by others the far northern GBR is not an area effected by large river discharges of anthropogenic nutrients (from agriculture) as is the case further south. 

Of course the presence of high nutrient concentrations, high turbidity and high phytoplankton biomass are not independent of one another and so the overall story is likely to be even more complex than I have made it out to be above.

Cheers

Jon  

-----Original Message-----
From: coral-list-bounces at coral.aoml.noaa.gov <coral-list-bounces at coral.aoml.noaa.gov> On Behalf Of Scott Wooldridge
Sent: Tuesday, 8 May 2018 8:43 AM
To: Coral -List <coral-list at coral.aoml.noaa.gov>
Subject: Re: [Coral-List] Coral on the Great Barrier Reef was 'cooked' during 2016 marine heatwave. REALLY? REALLY? REALLY? #2

 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)
> 5830 University Research Ct
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> urce=g>.,
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>
> "A world without coral reefs is unimaginable."
> Dr. Jane Lubchenco, March 25 2010
>
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