Scott Wooldridge S.Wooldridge@aims.gov.au via coral.aoml.noaa.gov

6:40 AM (3 hours ago) Thursday, May 2, 2013

to coral-list
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