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<P><FONT face=Arial size=2><FONT color=#0000ff>Dear James,<BR><BR>Interesting,
useful photos. Without knowing the precise oceanographic conditions of the
area at the time, the suggestions below will be speculations at best. But,
however, here goes (my two cents worth):</FONT></FONT></P>
<P><FONT face=Arial size=2><BR>Your question - Photo 1596 shows an Acropora sp.
bleaching from the center out. Why is this? <BR><BR><FONT
color=#0000ff>I would suspect that the secondary variables light and flow
(perhaps trapped by the morphology of this flat Acropora colony) have conspired
to increased the effect of the warmer than normal conditions. We should
also be mindful that most of the growth occurs on the outer edges (that are less
affected), and that the number of zooxanthellae are lower there as
well. The latter might mean less oxidative stress per host
cell and hence less bleaching.</FONT></FONT></P>
<P><FONT face=Arial color=#0000ff size=2></FONT><FONT face=Arial
size=2><BR>Photos 1594 and 1595 show a monospecific stand of Acropora. I
would expect either the whole colony to bleach, or perhaps the tops of branches
- however<BR>the coral is only bleached in large "patches." Why is
this? <BR><BR><FONT color=#0000ff>Two interpretations: (1) One
is that there are clonal (genetic) differences either in the host or the
zooxanthellae that create slightly different temperature thresholds for
bleaching stress (see paper by Pete Edmunds) OR (2) slight variations in
flow have interacted with the effects of temperature - producing different
patches.</FONT><BR><BR>Some of the photos show many different colonies in one
patch reef. Why is one coral bleached, and it appears that an identical
species next to it is<BR>not (1599 and 1600). Why did one coral bleach,
and the other did not?<BR><BR><FONT color=#0000ff>As above: Either it is
genetics or it is local secondary factors that vary across the reef.
History - feeding, reproductive condition, interspecies aggression etc) might
also play a role in determining behaviour under thermal
stress.</FONT><BR></P></FONT>
<P><FONT face=Arial color=#0000ff size=2>Cheers,</FONT></P>
<P><FONT face=Arial color=#0000ff size=2>Ove</FONT></P>
<P><FONT size=2>Professor Ove Hoegh-Guldberg<BR>Director, Centre for Marine
Studies<BR>University of Queensland<BR>St Lucia, 4072, QLD<BR><BR>Phone:
+61 07 3365 4333<BR>Fax: +61 07 3365
4755<BR>Email: oveh@uq.edu.au<BR></FONT></P>
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