Sponge Theory

[pardonmyreefing]

Noticed something interesting after I did my water change on Saturday. I usually like to feed the tank heavily and wait thirty minutes as well before changing the water, this includes phyto, reeftoids, and some mysis, I do the same for my other tank as well. Anyways, after maintenance I noticed that my spider sponges polyps were beginning to extend, this continued for the rest of the weekend. I don’t know if this is much of a “theory” or could just be an observation I’ve never seen until now (this is my first sponge). I’m thinking that since there was an abundance of nutrients in the water, the polyps jumped into action. They mostly open more at night but some during the day. I know a lot of people say it’s a parasitic relationship if the polyps outgrow the sponge, and while that may be true I think it’s just commensalism at play here, the polyps jumping at the opportunity for an easy snack, because most of the time the polyps of mine and even other sponges don’t open too often. I know this is me rambling but, I don’t know what do you guys think I thought it was interesting to think about.

 

[cristata.reef]

The relationship is technically parasitic, albeit a very prolonged case of parasitism. The polyps, a type of Epizoanthus, are commonly found growing on gorgonians, sponges, and black corals. This particular species has a natural affinity for the Australian sponge Trikentrion flabelliforme and subsequently encrusts on its surface. Since the biology of sponges dictate that in order to survive, the must receive constant and adequate water flow through the central cavity, the growth of the zoanthids is actually detrimental to it's health. Eventually the zoanthids will completely cover the sponge and starve it of nutrients.

I assume what you were referring to in your observation was the polyp extension from the zoanthids. This is actually the primary reason why they are parasitic. In the ocean, sessile invertebrates are often particulate feeders. Therefore their biological success is determined almost exclusively by the surface are of their feeding surfaces. If you think of the morphology of crinoids, sea fans, sea pens, feather dusters, etc you will notice that all of their feeding surfaces are geometrically designed to optimize surface area. Now back to our zoanthid friends. These guys are tiny (like truly tiny polyps). Realistically they don't have a competitive advantage over many other filter feeders on the reef. So how did they overcome this? By growing on a sponge of course. This extends their surface area vertically which allows them to feed from a larger area within the water column. And finally since they are colonial, they can share the captured food items making this strategy quite effective, of course until the sponge dies.

I hope you find this helpful