[Coral-List] Minor bleaching in the Marshalls

Dean Jacobson atolldino at yahoo.com
Tue Feb 22 00:10:26 EST 2005

Majuro is currently suffering renewed minor bleaching
(first noticed on Feb 13 2005) restricted to the reef
flat (chiefly small Acropora spp, such as A.
digitifera).  Perhaps this is related to the "hotspot"
to the south.  While this sort of shallow bleaching
(upper half meter or less) is not unusual (we had
similar bleaching in 2000, 2002 and 2004) what is
novel is the season; previous bleachings were limited
to the autumn (Sept-Nov) when maximal temperatures
occur.  A week later (Feb. 20) a dive computer gave a
temp. reading of 84 F at the surface and 82 F 10
meters down.  This bleaching is on the southern
leeward shore, sheltered from the tradewinds, during a
period of calm condition (i.e., minimal swell).

I would also like to thank all the people who
responded months ago to my coral area software
request.  ImageJ worked great; results will be
submitted for publication soon.

For those show don't want to wait, here is a summary:
I analyzed the area of over 800 colonies (those found
within a transect 20m by 120m), and calculated that
coral disease had killed 18% of tabulate Acroporas
over 50 cm in size during the 2004 calender year. 
Previous coral mortality was far less, so I caught
this outbreak in its early stages.  However,
additional area added by coral growth was probably in
the order of 20% or more.  (Fast growing tables add 1
cm to their radius each month, on average!)  One
particularly "crowded" patch (having over 48% live
tabulate coral cover, almost exclusively A. cytherea)
experienced a whopping 30% mortality in only 7 months,
with disease spreading to adjacent tables and shelves.
 There does not seem to be much seasonal variation in
disease initiation (I monitored the site 3-4x a month,
so I have pretty accurate data), perhaps a small spike
in August. 

Dean Jacobson
College of the Marshall Islands

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