Clean Cloud Sponge

Living Cloud Sponges appear clean with the main portions appearing pure white or yellow.

Dead Cloud Sponge

Dead sponges or dead portions of a living  sponge turn brown and are covered to varying degrees by sediment

Sediment accumulation over time.

In the laboratory we added thin layers of natural sediment on the sponge surface at various locations.  Over time the sediment moved downward on all but horizontal surfaces. This might occur in a few minutes (vertical surface) to a few days (slightly sloped surface). Some sediment also accumulated where branches came together.

Fresh sediment on sponge

The edges of what we interpret as growing mittens are soft, without a fused skeleton We observed sediment on horizontal mittens under a microscope over several days and saw no movement of particles. However, even a slight current caused all the sediment to be resuspended.

Hole formed under area where sediment had been added.

In one case sediment was added, and in 2 days a hole formed under sediment which subsequently fell through into the exhalent cavity of the sponge.

Zoom in of hole

Hole Closed Up

The hole then gradually got smaller and closed up after 21 days. This could be a mechanism for moving sediment deposited on soft tissue into the excurrent stream of the sponge. However, experiments are needed to see if this effect can be replicated.

Carmine newly added to the horizontal surface of a sponge

We added carmine particles to a horizontal surface with a fused skeleton

Carmine remaining on the surface after 14 days.

Over 14 days the amount of carmine appeared to gradually decrease. Observations of the inner surface of the wall with a dentist’s mirror did not reveal any carmine colour on the inside wall.

Photo showing vertical orientation of mittens.

It is of some interest to note that in many populations the mittens tend to be oriented with their flat surfaces vertical. This would limit potential sediment accumulation to the thin margins where water currents are likely to be greatest due to the baffling effect of the mittens and where holes might open to move sediment into the exhalent stream.  Even if sediment were to accumulate on the margins most of the mitten surface area would be clean and thus the rate of water intake through their surface would not be reduced due to clogging. 

Photo of sponges on sponge mat in Strait of Georgia

In areas likely to have high rates of sedimentation such as the sponge mat in the Strait of Georgia near the Fraser River, many of the sponges form straight cylinders with a minimum of horizontal or low slope surface. Without experimental manipulation we can only speculate that this form may be a response to high sediment loads.

Another aspect of keeping clean is to keep other organisms from using the sponge surface as a place to sit or attach. Many groups of aquatic organisms have chemical or mechanical defenses as antifouling devices. This is considered under associates.