


Growth
rings in Cloud Sponge
Some
sponges have rings on the inner surface which represent
differential growth. This might be in
response to increased nutrients or silica. However, we
can only speculate at the moment



Is there evidence elsewhere of
rapid growth rates? 
Doug Pemberton took this photo (December 2006) of a
large Cloud Sponge on the sunken vessel Columbia at Maude Island, at
a depth of about 20m.
While the
Columbia was sunk in June 1996, local divers assured Doug that there
were no Cloud Sponges on the hull until at least 2003 in which case
this sponge would be 3 years old.



A
63 cm Cloud Sponge on a Centra Gas pipeline that
had been submerged for 9 years indicated growth averaging
at least 7 cm/year.
(Randy Height Vacilador Productions
Ltd, Measurements
by Bill Austin) 


SUMMARY
1. Growth can be significant over the period of one
year. A greater than doubling of size in the present case.
2. Growth is limited to those portion of the sponge
which are still soft and do not yet have a fused mainframe
skeleton.
3. Growth may cease in some portions of the sponge
such as the “phallus” portion in this sponge.
4. Given that it is limited to soft areas, this
growth would tend to be an increasingly smaller portion of
the overall size. This assumes growth rates of soft portions
do not increase significantly with increased sponge size, a
condition which is unknown at present.
5. Growth, at least in the individuals assessed, does
not include a significant thickening with age.
6. Growth may be characterized in terms of increase
in surface area rather than in volume as the latter is
mainly water which is topologically outside the sponge walls
and does not directly represent any caloric expense. 



How long do these sponges live? 
One crude measure of age might be
size to the degree it reflects body mass. Since the thickness of the
body wall of A. vastus is essentially the same throughout
the sponge, the surface area is directly correlated with weight. 


Divers carefully enclosed a fragile,
moderate size sponge in a net. This sponge measured 0.65 m long x
0.48 m in diameter and occupied a space of about 0.12 cubic meters.
It was air dried for 4 months, and then weighed. Samples of known
surface area were weighed, and the weight per square cm times the
total weight was used to calculate the total surface area of the
sponge which was 3.68 square meters. 





A plot of the
square root of the surface area of the phallus sponge generated
a straight line

This line
intersected the square root of the surface area of the harvested
sponge at year 28

Assuming the
phallus sponge was 3 years old when first measured, and growth
rates were maintained, then the harvested sponge is estimated to
be about 30 years old.



Much
larger sponges occur on Senanus Reef


The table to
the right shows the sizes of large A. vastus found in Senanus
Reef
Sponges 25
times larger could be significantly older, or, alternatively, the
could have grown much faster. 



