[Coral-List] Fwd: CO2-limitation of algal endosymbionts in hospite is common

Scott Wooldridge swooldri23 at gmail.com
Sat Aug 19 03:19:52 EDT 2017

The increasing evidence-base indicating that intracellular CO2-limitation
underpins thermal coral bleaching has fundamental implications for the
irradiance/light levels used to undertake laboratory experiments to
investigate the bleaching phenomena and make inference about reef-scale
responses. Muscatine et al. (1989) showed that the onset of intracellular
CO2-limitation is light/depth dependent for a given symbiont density,
whilst Stimson and Kinzie (1991) showed that expulsion rates of
nutrient-elevated symbiont populations were highest during midday 'peak'
irradiance levels.

Therefore, if one is interested in studying intracellular CO2-limitation as
a potential bleaching phenomena, then it is necessary to utilise typical
midday irradiance levels of >500 and preferable >900 umol/m2/s(see Fig 3c
and Fig 7 in Wooldridge 2017). Field observation undertaken by Yentsch et
al. (2002) in the Dry Torgugas show that these are commonly observed summer
irradiance levels between 11am – 4pm on reefs at low-latitudes, even down
to 3m depths.


Now, I realise that for most-all laboratory set ups is is simply not
possible to keep corals alive and healthy at these irradiance levels. My
response? Then the laboratory set up is not suitable for investigating the C
O2-limitation bleaching mechanism.

Indeed, it appears that only outdoor (natural light) flow-through systems
using seawater drawn directly from reef waters are capable of achieving the
necessary experimental criteria. The Heron Island flow-through system is a gold
star in this respect (see e.g. Anthony et al. 2008; Kaniewska et al. 2015).
So too, the flume facility at the Hawaii Institute of Marine Biology
(see Stimson
and Kinzie 1991; Langdon and Atikionson 2005). I always treat the
experimental results from these setups with the highest regard, especially
in terms of symbiont population dynamics. Notably, both setups confirm the
importance of CO2-limitation of intracelluar symbionts on coral physiology
as the ocean warm and pCO2 levels rise (Langdon and Atikionson 2005;
Anthony et al. 2008; Crawley et al. 2010). And in particular, the
importance of the interglacial pCO2 level (260-280ppm) for symbiosis

eg1. From Langdon and Atikionson (2005)


eg2. From Anthony et al. (2008)


I think we should be very wary of laboratory responses that experiment on
the physiology or corals with light levels <350 umol/m2/s (the commonly
adopted level that allows small glass tank held corals with minimal
flow-through to stay alive for testing). To put this in perspective, for a
coral at a depth of 1m this is equivalent to testing with the light
intensity observed at 730 in the morning on a typical summer day (Yentsch
et al. 2002). Light driven CO2-limitation will not be enacted at such low
light levels.

My hat goes off to experimental scientists around the globe – I appreciate
how difficult, challenging, time consuming and expensive it is. I hope
these comments in no way comes across as criticism. I am just trying to
make the case for how we can better test (even falsify) the CO2-limitation
bleaching mechanism. Science works best when we endeavour to falsify ideas
rather than make inference by popular consensus.



Cited literature:

Anthony et al. (2008) Ocean acidification causes bleaching and productivity
loss in reef builders. PNAS105:17442-17446.

Crawley et al. (2010) The effect of ocean acidification on symbiont
photorespiration and productivity in Acropora formosa. Global Change
Biology 16:851-863

Kaniewska et al. (2015) Transcriptomic changes in coral holobionts provide
insights into physiological challenges of future climate change and ocean
change. PloS One 10(10):e0139223

Langdon C, Atkinson MJ (2005) Effect of elevated pCO2 on photosynthesis and
calcification of corals and interactions with seasonal change in
temperature/irradiance and nutrient enrichment. JGR *DOI: *

Muscatine L, Porter JW, Kaplan IR (1989) Reseource partitioning by reef
corals as determined from stable isotope composition. Marine Biology

Stimson J, Kinzie RA (1991) Journal of Experimental Marine Biology and
Ecology 153:63-74.

Yentsch et al. (2002) Sunlight and water transparency: cornerstones in
coral research. Journal of Experimental Biology and Ecology 268:171-183.

Wooldridge 2017 https://www.researchgate.net/publication/317100418_

---------- Forwarded message ----------
From: Scott Wooldridge <swooldri23 at gmail.com>
Date: Thu, Aug 17, 2017 at 9:11 AM
Subject: CO2-limitation of algal endosymbionts in hospite is common
To: coral-list at coral.aoml.noaa.gov

Dear Fellow Coral Reef Researchers,

Just drawing attention to this excellent new manuscript by Radecker et al.
which highlights well that, "CO2 limitation of Symbiodinium is a common
feature of stable cnidarian holobionts".


Results such as these provide strong support for the role of light- adn
temperature driven CO2-limitation as the primary driver of mass coral
bleaching events:


And explains why strongly autotrophic symbiotic corals are "the living
dead" in the Anthropocene ocean:


The results also infer the crucial importance of getting the
experimental/laboratory light requirements correct for testing bleaching
mechanism, and making inference from the lab to ecosystem scale. I will
write further on this in a separate listing.



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