[Coral-List] Nutrients / coral bleaching / coral mortality / coral disease

[Scott Wooldridge]

Hi Coral Listers,

This will be my last post on this issue - the time for talking is well
past, and good experiments by young scientist are what are required not
more rhetoric - by me or others.

For young scientists, the essential starting point for designing your
experiments is the recent paper by Baker et al. 2018, 'Climate change
promotes parasitism in a coral symbiosis'.

https://www.nature.com/articles/s41396-018-0046-8

The paper quickly establishes the essential truth of the matter - that
nutrient enrichment and climate change work interactively. The stress foci
is a destabilising of the energy relations of the coral-algae symbiosis.
The net result is a starving of the coral host energy reserves, which can
be understood to make corals more sensitive to thermal bleaching/mortality
(and coral disease, as shown by Vega Thurber et al. 2013, "Chronic nutrient
enrichment increases the prevalence and severity of coral disease and
bleaching")

https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.12450


When considering nutrient enrichment, the thresholds of concern are much
lower than one might imagine. Meaning that numerous natural and
anthropogenic sources are relevant. For example, terrestrial runoff
(surface and groundwater), offshore upwelling, even bird quano enrichment
on remote atolls.

Think that bird excrement can't make reefs nutrient replete ?

Then have a read of Hoegh-Guldberg et al. 2004, 'Nutrient-induced
perturbations to δ13C and δ15N in symbiotic dinoflagellates and their coral
hosts'

http://www.int-res.com/abstracts/meps/v280/p105-114/

This paper shows that the ENCORE experiments were undertaken in nutrient
replete water. This couldnt have been known before the experiments, but
that is the unfortaunate truth. For example the authors write, 'This
suggests that corals and their symbiotic dinoflagellates growing in the
unenriched control ENCORE patch reefs may have been relatively nutrient
replete and hence, relatively unresponsive to additional inorganic
nitrogen. This is also consistent with the conclusions of HoeghGuldberg &
Williamson (1999) who argue that the ambient ammonium concentrations at One
Tree Island lagoon  (from  bird quano) are sufficient to supply the
nitrogen demand of actively growing corals'.

I have written much on the co-dependence of nutrient enrichment to the
thermal bleaching response. Choose to ignore what i have written if you
like. But dont ignore these results. Start your experiments and thinking
from the standpoint of these results.

Maybe, like me, it will lead to you suggest that pCO2 enrichment (so-called
ocean acidification) is an additional player in all this.

https://www.researchgate.net/publication/317100418_Instability_and_breakdown_of_the_coral-algae_symbiosis_upon_exceedence_of_the_interglacial_pCO2_threshold_260_ppmv_the_''missing''_Earth-System_feedback_mechanism

It is exciting time for coral reef research. a huge natural experiment is
underway that has the potential to explain phenomenon form the micro scale
of the coral cell through to the global scale of climate change (such is
the importance of coral reefs).

The important thing - the take home message - as i retire to oblivion. Dont
be fooled into explaining coral bleaching only through the spectre of
thermal SST stress because that is the only good (global-wide) tool/dataset
available. As good as the NOAA SST products are, any analysis that utilises
them alone is missing at least 1/2 the storyline.

The image of a drunk man walking home from the pub looking for his lost
keys under the lamp posts comes to mind. He looks there in failed hope
because that is the only place the light is shining. Lets not make that
mistake.

scott

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