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

[Scott Wooldridge]

Hi Coral Listers,



Further to my call for an increased focus on the FRONT END of the coral
bleaching process, I suggest a fantastic early study was undertaken by
Malcom Shick et al. (1999)

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1999.44.7.1667



The study specifically focused on the host mycosporine-like amino acids
(MMA) response to elevated levels of UVR-mediated oxidative stress / ROS .
The additional demographic measures of the symbionts in response to
elevated ROS are the results that I believe are of greatest physiological
importance.



Taken straight from their Abstract, they explain that.. densities of
zooxanthellae in colonies of S. pistillata, Acropora sp., and Seriatopora
hystrix exposed to UVR for 15 d were only one-third of those in control
colonies unexposed to UVR. This net decrease in the number of zooxanthellae
in the corals (bleaching) occurred despite UV-stimulated increases in algal
cytokinesis and in the host cell-specific density of zooxanthellae in
hospite, increases that apparently destabilized the symbiosis and caused
expulsion of the zooxanthellae.



The resulting rank of bleaching response severity also explains why
Stylophora Hystrix is so bleaching sensitive in situ.  It had the greatest
number of zooxanthellae (per host gastrodermal cell), in addition to the
highest rates of zooxanthellae division. Which, can be summarised as – the
largest number of zooxanthellae acting as selfish parasites.



This type of study is the kind that I am calling for many more of.  Getting
straight at the fundamentals of the host-symbiont interactions in the lead
up to the visible bleaching response. Sure,
media-attention-grabbing-dramatic-mass-bleaching-consequences papers have
their place. But it is at the scale of host-symbiont interactions in the
days to week lead up to bleaching that we must concentrate, if we really
want to progress our science.



We have great new diagnostic tools than were available in 1999 that are
just waiting to be implemented in a targeted way.



For your consideration,



Scott Wooldridge