Coral Reef Sponges
In all their variety and abundance, coral reef sponges add an extra dimension of structural complexity and biodiversity to coral reef habitats.
The sponges (Phylum Porifera) are the most primitive all animals, lacking muscular, nervous, circulatory, or digestive systems of even the most rudimentary kind.
Sponges feed by filtering the surrounding seawater of extremely tiny organisms like bacteria and the smallest of plankton. The sponge body plan is simple, but elegantly designed for this purpose.
The external surface of the sponge body is covered with tiny pores called ostia into which water is forced inward (but never outward).
Water drawn in through the pores eventually reaches one or more internal cavities lined with another type of specialized cells called collar cells.
These are the driving force behind the pumping mechanism. The water is then forced out through the large body cavity opening called the osculum.
In the process, the collar cells trap tiny bacteria and other small organisms and pass them to other specialized cells for digestion. The water flow created by the collar cells also brings fresh oxygen-rich water to the working body cells and removes carbon dioxide.
Although sponges may not seem to be doing much, large specimens actually pump surprisingly quantities of water, often hundreds of gallons each day, as they feed. In fact, it has been estimated that together, all of the sponges in the Caribbean Sea filter an amount of water about equal to the volume of the entire sea itself every single day
Some coral reef sponges are known to use “chemical warfare” to bore their way into living coral heads, thereby creating their own living spaces.