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

Tim Wijgerde wijgerde at coralpublications.com
Mon Aug 21 03:41:02 EDT 2017

Hi Scott,

Thanks for your interesting posts on coral list! Your theory of CO2 limitation matches well with our recent publication in JEB, in which we suggest that increased water flow and CO2 supply augment photosynthesis rates in Galaxea fascicularis:


Regarding your comments about limiting irradiance and water flow in aquarium setups, it is now quite easy to replicate nature in this respect. My own new lab, which I built under my house (and which I dubbed CORALAB), uses powerful LED lights and lots of Tunze streamers to provide Acropora spp. and other corals with a high energy environment. PAR levels of 750-1000 umol photons m-2 -s1 are quite easy to obtain using only two 190W LED lights. I probably can't mention the brand here, but people can always email me if they need more info. Spectral properties can also be manipulated. 

Here is a photo of my setup with the LED lights:




-----Original Message-----
From: coral-list-bounces at coral.aoml.noaa.gov [mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of Scott Wooldridge
Sent: Saturday, August 19, 2017 9:20 AM
To: coral-list at coral.aoml.noaa.gov; scott wooldridge <swooldri23 at gmail.com>
Subject: [Coral-List] Fwd: CO2-limitation of algal endosymbionts in hospite is common

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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