[Coral-List] Fw: Coral immortality

[Douglas Fenner]

This in from Dr. Janice Lough, an expert on the skeletons of massive Porites:


----- Forwarded Message ----
From: Janice Lough <J.Lough at aims.gov.au>
To: Douglas Fenner <douglasfenner at yahoo.com>
Sent: Wed, March 23, 2011 11:48:50 AM
Subject: RE: [Coral-List] Coral immortality


Hi Doug
 
Good to hear from you and hope all is well.
 
As you know AIMS has an extensive collection of Porites coral cores both from 
the GBR and, more recently, collected from  reefs off Western Australia.  
Obviously, this collection is based (biased?) on cores from living and 
apparently healthy Porites colonies though there are a handful collected from 
dead corals.  Although there is some evidence of a growth/age affect on skeletal 
density (see attached 2 papers), with skeletal density tending to decrease from 
old to young I have never come across any clear signals of reduced or declining 
growth prior to death of a colony.  There are, in some cores, signs of partial 
mortality and then regrowth (see, for example, Hendy et al 2003 attached) and 
there is also evidence of growth hiatuses and subsequent slowed growth for a few 
years following, for example, bleaching events (Lough, in prep).  

 
A recently collected core from a dead Porites in the Houtman Abrolhus (WA) – 
(see attached X-ray), shows fast extension rates and clear banding and then it 
died!  There is also  evidence of bio-eroders at the dead outer surface but 
(from this and other evidence) I am pretty convinced that these are post-death 
and not a cause of death.
 
Another consideration, at least for Porites, is that any individual coral polyp 
is likely to be < 10 years old (see Darke and Barnes (1993), attached) – so it 
is not the coral that is several hundred years old rather the skeleton has been 
formed over that time.  Though, as indicated in this paper, individual polyps 
may be much longer lived in other massive species.
 
I am unaware of any evidence for synchronized mass die offs though there can be 
synchronized growth hiatuses due to environmental stress (e.g. thermal 
associated with coral bleaching). There are also, as far as I am aware, few 
studies of the demographics of massive (or other) corals on reefs - Potts et al 
 (1985) is the only one I can think of.
 
So, I don’t think massive Porites are immortal but, at the same time, I don’t 
know why they die...................may be better question for a coral 
physiologist.
 
Hope this helps somewhat & best wishes
 
Janice
 
Dr Janice M Lough
Senior Principal Research Scientist
Australian Institute of Marine Science
PMB 3, Townsville MC
Queensland 4810
AUSTRALIA
 
e-mail: j.lough at aims.gov.au

Darke, W.M.,  Barnes, D.J.  1993.  Growth trajectories of corallites and ages of 
polyps in massive colonies of reef-building corals of the genus Porites.  Marine 
Biology 117: 321-326.

Lough, J.M.  2008.  Coral calcification from skeletal records revisited.  Marine 
Ecology Progress Series 373: 257-264.   Open access

Potts, D.C., Done, T.J., Isdale, P.J., Fisk, D.A.  1985.  Dominance of a coral 
community by the genus Porites (Scleractinia).  Marine Ecology Progress Series 
23: 79-64.   open access


Hendy, E.J., J.M. Lough, M.K. Gagan.  2003.  Historical mortality in massive 
Porites from the central Great Barrier Reef, Australia: evidence for past 
environmental stress?  Coral Reefs 22: 207-215.  



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