The Eastern Gulf of Mexico off Tarpon Springs is a rich area particularly in regards to encrusting organisms. This area is well known for the Greek sponge industry that developed earlier this century. Now it is the home of several live rock farms. In addition to several species of hard corals that grow on the rock are a host of colorful sponges and tunicates.|
These two groups are very similar in appearance to the naked eye, yet are quite different. Sponges are very simple organisms while at the other extreme, the tunicates are highly developed animals including a nervous system. Identification is often quite difficult for both of these groups as growth patterns are strongly affected by environmental conditions so shape and color can be quite variable. Both groups produce thin encrusting as well as lumpy shaped masses. In general the sponges are more colorful. Currently, we are harvesting rock with a range of colorful sponges.
Orange sponges come in a number of forms. The Orange ball sponge (Cinachyra sp.) is a distinct ball shape while the encrusting orange sponge (Mycale laevis) and the orange lumpy sponge (Ulosa hispida) can have many shapes. There are also yellow boring sponges (Siphodictyon sp. and Clioa sp.) that can appear as yellow dots or an encrusting mass. Red encrusting sponge masses (Diplastrella sp.) offer another attractive type. Encrusting tunicates can also be found that include brown (Botrylis sp.), red, blue-grey (Tridemnum sp.), white (Didemnum sp.), etc. The most dramatic are the blue sponges. We have at least two varieties. One has a spiky texture with miniature tubes (Dysidea sp.) and another that appears to be a blue variety of bread crumb sponge.
These blue sponges are thought to be the food of the colorful Greek goddess nudibranch (Hypselodpris edenticulata). These beautiful creatures only feed on this sponge so some wonder if they should be kept in reef tanks. On the other hand they may only live a few months in the wild. We just started to see them again this month after an absence on the reef since last spring. It has been suggested that their natural seasonal life cycle may be quite short and they may last as long in the aquarium as on the reefs.
Sponges may be a useful addition to reef tanks as they are filter feeders specializing in very small particles such as bacteria and smaller. Because they feed on such small particles, from several microns to less than a micron, they may not be competing with other filter feeders that eat zooplankton or algae. In theory they could reduce bacterial levels in the water taking out things that pass through the finest mechanical filters.