The Environmental Gradient

The Porifera (Living Sponges)

The living sponges that are utilized within the cryptic zones of the EG filtration systems are cryptic sponges. These sponges are quite prolific on the natural reef platform but are difficult for casual divers to locate. They avoid direct light since they typically lack any method to shield themselves from UV radiation. Cryptic sponges are found in cracks, crevices and other low light areas in shallow water. In deeper waters they are more prolific and can dominate in the very deep twilight areas of tropical reef platforms. These sponges are heterotrophic and acquire all their nutrition from external organic materials and lifeforms. Bacteria, phytoplankton, very fine particulate matter and dissolved organics are their primary food source.
There are also some sponges that are partially autotrophic due to symbiotic cyanobacteria. These sponges typically inhabit the semi-exposed zones where light levels are weak to moderate. We have used some of these sponges and they can be quite colorful due to their cyanobacterial symbionts. The sponges that are normally exported for the captive aquarium trade are exposed sponges that are easy for collectors to locate and harvest. These sponges are normally much too large for the aquariums they are put into. Large sponges like these need external food added and also have suffered from transportation stress. The sponges that we utilize in cryptic zones are typically found as very small sponges on live rock, on the base rock of exported coral colonies and on old rocks within aged captive reefs.