Sponge Bleaching in Belize

[dixon@wgs1.btl.net]

Greetings from Belize:

As a result of increased water temperatures and solar radiation,
corals of the Orders Milliporina and Scleractinia have been reported
to have been experiencing varying degrees of bleaching throughout
their range.  In Belize, the corals are also bleaching again, as has
been announced.

However, no mention has been made of the effect of increased
temperature and radiation on other invertebrates that harbor
endosymbionts.  In fact, along the barrier reef and reef around
Lighthouse Atoll in Belize from 10-20 meters depth, a Poriferan,
Xestospongia muta,  has also been "bleaching."  The bleaching was
noticed shortly after plate Agaracia began bleaching in late
August.  In some cases, the first sign of bleaching is hidden by a 
thin layer of sediment.  When the sediment is fanned away, white 
spots become noticeable in the pinacoderm.  While the touch of a 
healthy specimen can be comparable to a red clay brick, the white 
spots of a diseased sponge are soft to the touch.  At the present 
time, where the white spots first appeared,  they have now begun to 
enlarge and holes are beginning to develop where the mesohyl has 
completely deteriorated and if fanned, resembles white pillow foam.

In Belize during the bleaching event of 1995, the bleaching of
Xestospongia muta was also observed.  Some specimens survived the
bleaching, but others completely deteriorated.  At the onset of 
sponge bleaching in 1998 in Belize, only a few individuals were 
observed with white spots. However, as temperatures have remained 
high during September, the number of individuals affected is 
increasing.  Present observations will rarely locate a completely 
healthy specimen.

Literature located via the Net on sponge bleaching included only 2 
reports found within CHAMP's web site.  In 1990 Vicente identified 
sponges and their endosymbionts in Puerto Rico during the 1987 
bleaching event.  The abstract concluded that "only a few individuals 
within any given population became bleached."

An updated version (1995) of Pecheux's internal report titled "Review
on Coral Reef Bleaching" describes a red-colored
phycoerythrin-bearing cyanobacteria, Aphanocapsa, that lives
intracellularly in specialized cyanocytes and also the mesohyl of 
Xestospongia muta.  It also went on to say that bleaching in sponges 
appears uncommon and that Vicente had reported a frequency of 10-30% 
of bleached Xestospongia muta at 4-15 meters depth.

If temperatures and radiation remains high, individuals of
Xestospongia muta may succumb as did some in the 1995 bleaching 
event.

Has any one else observed bleaching of Xestospongia muta in its 
range during the 1998 bleaching event, or does anyone know of  more 
recently published reports that describe this phenomenon?

Linda Wetrhus
SYMBIOS/ECO
PO Box 1234
Belize City, Belize
TEL: (501) 2-35505
FAX: (501) 2-75213
Email: seasprtsbz at btl.net