by Katie Kaiser, FSUCML graduate student
Sponges! Absorbent and colorful with many different irreplaceable functions! Sponges are one of the only organisms that can directly filter bacteria sized particles from the water column. They filter at incredible rates and efficiency, clearing at least 95% of bacteria from the water. Loss of sponges in Florida Bay has been linked to increases in phytoplankton blooms, which are devastating to sponges, fish, and many benthic invertebrates.
Besides their awesome filtering abilities sponges are also involved in a myriad of interactions. Sponges can be considered “living hotels” to hundreds of species of tiny animals such as sea spiders, worms, crustaceans, and brittle stars. Some symbiont species use the sponge as both a refuge and a food source!
Crustaceans can provide a mobile home for sponges, and in turn one species of hermit crab lives inside a sponge that completely covers its shell and then continues to grow as the hermit crab grows; and decorator crabs can choose to decorate themselves with sponges that camouflage them from their predators!
Sponges growing on mangrove roots protect them from small crustaceans that bore holes in the roots, killing the tree. In turn, the mangrove roots provide a stable substratum for the sponges in a habitat with abundant plankton on which sponges feed.
Sponges glue corals onto reefs, and protect the vulnerable undersides of corals from organisms that bore holes in coral skeletons. Sponges also filter bacteria out of the water column, maintaining clear water required by corals.
Sponges and zooanthids can protect each other from predators. Zooanthids are tiny colonial anemones that embed themselves in the surfaces of sponges, living in close association for the rest of their lives as a sort of 2-species ‘super-organism’.
Sponge predators include Hawksbill sea turtles, angelfish, starfish, and nudibranchs! Sponges have unique chemical defenses that deter most predators, but angelfish overcome this by eating small portions of each of many different sponge species. Sea stars will “taste” a sponge with their tube feet then, if they like it, they climb onto it and release digestive enzymes. Nudibranchs eat a crevice into the sponge and then remain tucked inside.