Natural History : Growth & Age : Page 2                                                                            << Page 1

Mittens of a Cloud SpongeThe translucent whitish mitten edges lack a fused skeleton.   

   

Osculum of Cloud sponge

Growth also occurs around the oscula (exhaust openings) where the tissue is soft.  

   
Below are photographs of the same sponge alive on the left and after death on the right,

The open areas on the dead sponge are those which were covered by soft tissue without a fused skeleton. The widest area surrounded the osculum or exhaust opening.
 
   

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.

 

  • Sponge samples were taken near the base and at the apices of live sponges and from a dead stump

     

  • We sent the samples to a specialist in California hoping he could tell us how old they were.  

     

  • He could not, so we still don’t know how long       these sponges can live.

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