[Coral-List] So you think you understand coral bleaching?

[Scott Wooldridge]

Hi Steve,



As you may have picked up, I was extending my comments to their
thought-provoking extremes. Obviously, many scientists are doing innovative
work on trying to better understand the inner working of the coral
bleaching process. Indeed, I read a great summary report in a recent issue
of PNAS, which is well worth a read.



https://www.pnas.org/content/117/5/2232.short



You are also correct that many scientists, managers and policy makers have
been striving to improve reef water quality as an important conservation
measure.



What I will say, however, is that what I am advocating is not the idea that
poor water quality is just one (of many) additive stresses that impact on
coral reefs, i.e. a contributing straw that helps breaks the camel’s back.
Instead, I envisage inorganic nutrient enrichment as an intrinsic,
co-determining driver of thermal coral bleaching. That is, excess nutrient
enrichment increases the likelihood of coral bleaching (per unit thermal
anomaly).  To understand this better, and how it interacts with our efforts
to reduce future rates of global warming, check out:



https://www.researchgate.net/publication/235762816_Safeguarding_coastal_coral_communities_on_the_central_Great_Barrier_Reef_Australia_against_climate_change_Realizable_local_and_global_actions

Abstract

The threats of wide-scale coral bleaching and reef demise associated with
anthropogenic (global) climate change are widely known. Less well
considered is the contributing role of conditions local to the reef, in
particular reef water quality, in co-determining the physiological
tolerance of corals to increasing sea temperatures and declining pH. Here,
the modelled benefit of reduced exposure to dissolved inorganic nitrogen
(DIN) in terrestrial runoff, which raises the thermal tolerance of coastal
coral communities on the central Great Barrier Reef (Australia), is
considered alongside alternative future warming scenarios. The simulations
highlight that an 80% reduction in DIN ‘buys’ an additional ~50–60 years of
reef-building capacity for No Mitigation (‘business-as-usual’) bleaching
projections. Moreover, the integrated management benefits provided by: (i)
local reductions of ~50% in DIN contained in river loads, and (ii) global
stabilisation of atmospheric CO2 below 450 ppm can help ensure the
persistence of hard-coral-dominated reefscapes beyond 2100. The simulations
reinforce the message that beyond the global imperative to mitigate future
atmospheric CO2 emissions there still remains the need for effective local
management actions that enhance the resistance and resilience of coral reef
communities to the impacts of climate change.



I hope this clears up some misconceptions, and assures people that beyond
water quality improvements I DO also advocate strongly of the importance of
reducing our carbon footprints.



But the central tenet of my previous post remains. We need to keep pressing
for a more comprehensive understanding of the coral bleaching mechanism. It
is not perfectly understood. Lots still remains to be discovered. And we
should be excited by the challenges that presents, and the hope that
remains for finding solutions to help save coral reefs from extinction.


For your consideration,



Scott


>
> Message: 3
> Date: Wed, 25 Mar 2020 16:26:46 -0400
> From: sealab at earthlink.net
> To: Scott Wooldridge via Coral-List <coral-list at coral.aoml.noaa.gov>
> Cc: coral list <coral-list at coral.aoml.noaa.gov>
> Subject: Re: [Coral-List] So you think you understand coral bleaching?
> Message-ID: <31dd1334-25d8-4ffa-9193-bcdf8e2774c4 at Steves-iPad>
> Content-Type: text/plain; charset="utf-8"
>
>
>
> Hi Scott,
>
> Your ideas certainly raise some interesting points. I agree that the reef
> science community here can sometimes get bogged down discussing how to
> minimize our carbon footprints, but I was struck most by your assertion
> that instead, finding a CURE for bleaching should consume ?99.9% of the
> best thinking time? of coral reef scientists. As I view it, coral
> scientists are in no way resigned to the belief that reducing global carbon
> emissions is the ?sole solution?. If anything, there are already great
> efforts being made to divert attention away from the need to address
> climate change and towards an efficacy favoring restoration involving some
> form of enhanced resistance. These projects may not be based on the FRONT
> END of the bleaching response as you described, but they are focused on
> similar goals. In addition, if the favorable symbiotic conditions you seek
> are dependent on ?ensuring a severe limitation of the seawater supply of
> nutrients? - haven?t we been striving for this all along?
>  It sounds to me like the venerable call for improvements in water quality
> that many have been advocating for years. Let?s just imagine that the
> supply of nutrients was miraculously brought under control and water
> quality was restored. With that elusive goal achieved, wouldn?t it be
> better to work to reduce carbon emissions and then let nature take its
> course? Why would we want to turn our backs on trying to solve the
> existential problem that is climate change with all of its implications for
> both marine and terrestrial ecosystems in search of a highly improbable
> ?cure? or coral bleaching? What could be better than envisioning a scenario
> whereby we effectively address climate change AND restore water quality
> thereby reducing widespread bleaching and outbreaks of coral diseases all
> in one fell swoop? That?s what I would call going for the gold! If our
> current crisis with COVID-19 teaches us anything, it should serve as
> testimony to the connectivity and fragility of life on this planet
>  . A lesson that we would all do well to apply to climate change and the
> many challenges it presents to us all.
>
> Regards,
>
> Steve
>
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> nd of Coral-List Digest, Vol 139, Issue 19
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