[Coral-List] Fw: Coral immortality
douglasfenner at yahoo.com
Wed Mar 23 21:59:18 EDT 2011
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
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
Hope this helps somewhat & best wishes
Dr Janice M Lough
Senior Principal Research Scientist
Australian Institute of Marine Science
PMB 3, Townsville MC
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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