Growth, Size & Lifespan
This page discusses estimates of growth, size and lifespan of reef-forming glass sponges based on work conducted on a BC south coast glass sponge reef, work initiated by Dr. Willian C Austin, Director, Khoyatan Marine Laboratory. The study was conducted in 2006 by volunteer divers under the lab’s direction.
Divers measuring height of a moderate size Cloud Sponge. Divers placed markers next to 8 Cloud Sponges and then measured their height and photographed them periodically over a period of one year.
Divers measuring height of a small Cloud Sponge. Height is only one parameter of growth and parallax and viewing angle may have resulted in some degree of error.
Next 5 photos of same sponge over a period of one year. The best results to date are from measurements of a flattened mitten-like form of a small sponge by divers Mike Miles and Joe Doiron.
The phallus like part of the sponge is roughly cylindrical so that an estimate of the surface area is best determined as that of a cylinder closed at one end. The non-growing phallus is 18.3 cm long and 3.3 cm in diameter, resulting in a surface area of 160 square centimetres. The mitten like part of the sponge is comprised of 2 broad fairly flat surfaces together forming a flattened sac.
Areas of the broad surfaces were determined graphically by Bill Austin, Khoyatan Marine Lab, and electronically by Sheri Ward, Coastal and Ocean Resources. The two methods of calculating area were in close agreement (within 1 sq. cm.). The initial surface area on one side (excluding the “holdfast” ) was about107 square cm while the surface area after one year had increased to 253 square cm., a 136 % increase in size.
No direct measurements of thickness were made as removing samplesmight affect subsequent growth. Measurements on another similar sized sponge were taken at 5 cm, 10 cm, 15cm and 20 cm from the growing edge. The thickness for this sponge was 6mmfor all but the lowest (20 cm) which was 5.5 mm.
We reported in a paper (Austin et al 2007) on Growth over a 3 ½ year period. Growth in surface area is perhaps most meaningful, but except for juveniles, can’t be measured without killing the sponge.
Where does growth occur?
Measurements of the phallus sponge over time indicates that growth is apical rather than throughout the sponge. To independently verify where growth occurs, divers drilled two holes and measured the distance between the holes, as well as, between the osculum, or sponge vent, and the closest hole. They returned 2 ½ and 3 ½ months laterand re-measured these distances. Note the regeneration can occur at the broken edges of fused skeleton.
- The results for 2 sponges are shown in the table above
- The distance between 2 bored holes is unchanged
- While the distance between the osculum and the near hole has increased significantly
- Growth is limited to the soft parts where the mainframe skeleton hasn’t fused together. Regeneration can also occur at the broken edges
Mittens of a Cloud Sponge. The translucent whitish mitten edges lack a fused skeleton.
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.
Osculum of Cloud sponge Growth also occurs around the oscula (exhaust openings) where the tissue is soft.
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?
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)
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.
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 significantthickening with age.
6. Growth may be characterized in terms of increase in surface area rather thanin 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?
The glass sponge was thought to have gone extinct 40 million years ago, but the animal was discovered in B.C. in the early 1970's. Some of B.C.'s glass sea sponge reefs are thought to be 9,000 years old.
One crude measure of age might be size to the degree it reflects body mass. Since the thickness of the body wall of Aphrocalistes vastus is essentially the same throughout the sponge, the surface area is directly correlated with weight.
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 weremaintained, then the harvested sponge is estimated to be about 30 years old.
Much larger sponges occur on Senanus Reef
This table 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.
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.
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.