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

Bruno, John jbruno at unc.edu
Mon Apr 23 08:36:02 EDT 2018

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.researchgate.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
🐠🐋🧜‍♂️🐟🦐 🦈🦑

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