[Coral-List] A new explanation for the how? and why? of coral calcification

[Scott Wooldridge]

For both the geologist and biologist alike, the extending dimension of coral skeletal growth (i.e. skeletal extension) is often considered a good indicator of the efficient functioning of the coral-algae symbiosis. In a new manuscript in Biogeosciences I outline why this conceptualisation can be misleading. This new explanation provides insight into: (i) why fast growth at optimal temperatures is often a reliable indicator of ‘bleaching sensitivity’ under thermal stress, (ii) why the gross skeletal morphology of a coral changes with variable environmental conditions (nutrients, pco2, light, SST, flow), and (iii) why this challenges the development of reliable paleo-climate proxies based on coral skeletons.
Wooldridge, S (2013) A new conceptual model of coral biomineralisation: hypoxia as the physiological driver of skeletal extension, Biogeosciences, 10, 2867-2884.
http://www.biogeosciences.net/10/2867/2013/bg-10-2867-2013.pdf

The manuscript builds upon ideas and concepts developed in another recently published Biogeosciences manuscript which explains why enlarged and fast-growing endosymbiont populations - as permitted by the modern envelope of  seawater conditions (characterised by elevated temperatures, rising pCO2, and enriched nutrient levels) – are conspiring to lower the thermal ‘breakpoint’ of the coral-algae symbiosis.
Wooldridge, S (2013) Breakdown of the coral-algae symbiosis: towards formalising a linkage between warm-water bleaching thresholds and the growth rate of the intracellular zooxanthellae, Biogeosciences, 10, 1647-1658.
http://www.biogeosciences.net/10/1647/2013/bg-10-1647-2013.pdf

In their separate ways, the two papers support the case that the optimal (stable) pCO2-SST-light-nutrient envelope for the coral-algae symbiosis was transgressed for most global reef sites long before the first ‘visual’ recordings of mass bleaching in the early 1980’s. For those interested, I have previously outlined in another Biogeosciences manuscript the available evidence to suggest that the interglacial pCO2 threshold (<260ppm) is a key stability threshold for the coral-algae symbiosis.
Wooldridge, S (2012) A hypothesis linking sub-optimal seawater pCO2 conditions for cnidarians-Symbiodinium symbioses with the exceedence of the interglacial threshold (>260ppmv), Biogeosciences, 9, 1709-1723.
http://www.biogeosciences.net/9/1709/2012/bg-9-1709-2012.pdf

Scott Wooldridge
Research Scientist
Climate Change and Ocean Acidification Team
Australian Institute of Marine Science


--  
------------------------------------------------------------------------
The information contained within this transmission is for the
use of the intended recipient only and may contain confidential
and/or legally privileged material and/or material the subject
of copyright and/or personal information and/or sensitive
information that is subject to the Privacy Act 1988. Any review,
re-transmission, disclosure, dissemination or other use of, or
taking of any action in reliance upon, this information by
persons or entities other than the intended recipient is
prohibited. If you have received this email in error please
notify the AIMS Privacy Officer on (07) 4753 4444 and delete
all copies of this transmission together with any attachments.
------------------------------------------------------------------------