[Coral-List] Fast extension rates don’t always equate to a healthy coral

Andrew Ross ross.andrew at mac.com
Fri Apr 10 10:14:12 EDT 2015

Scott and I and others have discussed a little bit already and it might be worth bringing up here:
When I was young and energetic I measured Acropora cervicornis apical polyp extension weekly for about 5-months, including through death in the 2005 Caribbean bleaching event.
Extension rates increased in the days/weeks leading up to and into bleaching, including the times of highest water temperatures. Bleaching didn’t set in in earnest until temperatures had started to wane. 
This was Montego Bay, Jamaica, where the water is generally warm (28C) and enriched.
In the week(s) of full bleaching leading to final death, I often noted shrinking inclusive of skeleton, though this was likely just in the soft apical skeleton. 
The formal paper is maybe 60% complete. If anybody is curious, it’s in my thesis on ResearchGate.

> On Apr 9, 2015, at 6:25 PM, Scott Wooldridge <S.Wooldridge at aims.gov.au> wrote:
> Just following on from Doug’s comments.  The paper can be downloaded from my ResearchGate page.
> Wooldridge SA (2014) Assessing coral health and resilience in a warming ocean: why looks can be deceptive. BioEssays 36(11):1041-1049
> Abstract: In this paper I challenge the notion that a healthy and resilient coral is (in all cases) a fast-growing coral, and by inference, that a reef characterised by a fast trajectory toward high coral cover is necessarily a healthy and resilient reef. Instead, I explain how emerging evidence links fast skeletal extension rates with elevated coral-algae (symbiotic) respiration rates, most-often mediated by nutrient-enlarged symbiont populations and/or rising sea temperatures. Elevated respiration rates can act to reduce the autotrophic capacity (photosynthesis:respiration ratio) of the symbiosis. This restricts the capacity of the coral host to build and maintain sufficient energy reserves (e.g. lipids) needed to sustain essential homeostatic functions, including sexual reproduction and biophysical stress resistance. Moreover, it explains the somewhat paradoxical scenario, whereby at the ecological instant before the reef-building capacity of the symbiosis is lost, a reef can look visually at its best and be accreting CaCO3 at its maximum.
> I also have a soon-to-be published manuscript which highlights that bleaching-sensitive reef areas on the Great Barrier Reef during the 1998 and 2002 mass bleaching events include old massive Porites colonies that have multi-decade sclerochronological histories characterised by regionally-enhanced skeletal extension rates (and reduced skeletal densities) outside of the bleaching events.
> Cheers,
> scott
> --  
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