bleaching and cloud cover

Peter J Mumby p.j.mumby at ncl.ac.uk
Fri May 18 19:05:57 EDT 2001


Following the interesting discussion on spatial patterns of bleaching, I =
thought I'd mention our observations from the Society Islands, French =
Polynesia. In 1998, the incidence of mass bleaching was patchy at scales =
of 10s - 100s km. Interestingly, bleaching was minor in Tahiti and =
Moorea despite positive SST anomalies being of similar magnitude and =
duration to previous years in which mass bleaching occurred. =
Meteorological data also revealed that wind speeds were exceedingly low  =
which is usually consistent with the onset of mass bleaching. However, =
although sea temperatures were elevated and the conditions were calm, =
cloud cover was very significantly greater than that associated with =
mass bleaching events (or other years for that matter). We used data on =
SST, wind speed and cloud cover to create a discriminant function that =
hindcasted the onset of mass bleaching in the area. Predictions for 1998 =
(i.e. minor bleaching) were only correct if cloud cover was explicitly =
incorporated into the analysis (i.e. in addition to temperature).=20
=20
Laboratory studies have shown that bleaching can occur on a scale of =
seconds or minutes under conditions of solar stress, but how do such =
responses reconcile with the large spatial scale of mass bleaching =
events? Although high cloud cover reduced overall levels of solar =
radiation at a large (island) scale, we have no biophysical =
understanding of the interaction between solar irradiance, cloud cover =
and bleaching. Measurements of cloud cover are unable to reveal the =
intensity and duration of incident irradiance so if high cloud cover did =
help prevent bleaching, we don't know whether it was because overall =
light budgets were reduced or whether the frequency of intense episodic =
bursts of irradiance was reduced. Anyway, food for thought...

More details are available in Mumby PJ, Chisholm JRM, Edwards AJ, =
Andrefouet S, Jaubert J (2001) Cloudy weather may have saved Society =
Island reef corals during the 1998 ENSO event. Marine Ecology Progress =
Series (in press)

Sorry if this was a bit long.=20

Cheers

Pete
=20

Dr Peter J. Mumby
Royal Society University Research Fellow

Centre for Tropical Coastal Management Studies
Department of Marine Science and Coastal Management
Ridley Building
The University
Newcastle upon Tyne
NE1 7RU
UK
tel: +44 (0)191 222 6228
fax: +44 (0)191 222 7891
email: p.j.mumby at ncl.ac.uk
http://www.ncl.ac.uk/tcmweb/ctcms/mumby.shtml

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<DIV><FONT face=3DArial size=3D2>Dear all,</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Following the interesting discussion on =
spatial=20
patterns of bleaching, I thought I'd mention our observations from the =
Society=20
Islands, French Polynesia. In 1998, the incidence of mass bleaching was =
patchy=20
at&nbsp;scales of 10s - 100s km. Interestingly, bleaching was minor in =
Tahiti=20
and Moorea despite positive SST anomalies being of similar magnitude and =

duration to previous years in which mass bleaching occurred. =
Meteorological data=20
also revealed that wind speeds were exceedingly low&nbsp; which is =
usually=20
consistent with the onset of mass bleaching. However, although sea =
temperatures=20
were elevated and the conditions were calm, cloud cover was very =
significantly=20
greater than that associated with mass bleaching events (or other years =
for that=20
matter). We used data on SST, wind speed and cloud cover to create a=20
discriminant function that hindcasted the onset of mass bleaching in the =
area.=20
Predictions for 1998 (i.e. minor bleaching) were only correct if cloud =
cover was=20
explicitly incorporated into the analysis (i.e. in addition to =
temperature).=20
</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Laboratory studies have shown that =
bleaching can=20
occur on a scale of seconds or minutes under conditions of solar stress, =
but how=20
do such responses reconcile with the large spatial scale of mass =
bleaching=20
events? Although&nbsp;high cloud cover&nbsp;reduced overall levels of =
solar=20
radiation at a large (island) scale, we have no biophysical =
understanding of the=20
interaction between&nbsp;solar&nbsp;irradiance, cloud cover and =
bleaching.=20
Measurements of cloud cover are unable to reveal the intensity and =
duration of=20
incident irradiance so if high cloud cover did help prevent bleaching, =
we don't=20
know whether it was because overall light budgets were reduced or =
whether the=20
frequency of intense episodic bursts of irradiance was reduced. Anyway, =
food for=20
thought...</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>More details are available in Mumby PJ, =
Chisholm=20
JRM, Edwards AJ, Andrefouet S, Jaubert J (2001) Cloudy weather may have =
saved=20
Society Island reef corals during the 1998 ENSO event. Marine Ecology =
Progress=20
Series (in press)</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Sorry if this was a bit long. =
</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Cheers</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Pete</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Dr Peter J. Mumby<BR>Royal Society =
University=20
Research Fellow</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Centre for Tropical Coastal Management=20
Studies<BR>Department of Marine Science and Coastal Management<BR>Ridley =

Building<BR>The University<BR>Newcastle upon Tyne<BR>NE1 =
7RU<BR>UK<BR>tel: +44=20
(0)191 222 6228<BR>fax: +44 (0)191 222 7891<BR>email: <A=20
href=3D"mailto:p.j.mumby at ncl.ac.uk">p.j.mumby at ncl.ac.uk</A><BR><A=20
href=3D"http://www.ncl.ac.uk/tcmweb/ctcms/mumby.shtml">http://www.ncl.ac.=
uk/tcmweb/ctcms/mumby.shtml</A></FONT></DIV></BODY></HTML>

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