We’ve probably all had a bath or shower at some point and used a natural sponge without thinking of where it has come from, but this is just one of thousands (some sources say 8550, others up to 10,000) of species of sponge that can be found in the oceans.
A member of the phylum Porifera, meaning pore bearer, sponges are simple multi celled organisms, so simple that they don’t even have nervous, circulatory or digestive systems. They are found in oceans all over the world and very diverse, coming in many different colours, shapes and structures.
Sponge are sessile creatures (fixed in one position and do not move) and can be both free standing and encrusting on surfaces.
Sponges may have a skeleton of spicules, a structural element, made of silica, calcium carbonate and spongin, a protein. Not many organisms eat sponges as some contain toxins, which prevents other sessile animals from living on them, and their spicules are probably hard to digest. But there are a few fish, hawksbill turtles and some nudibranchs that will eat them.
They rely on water constantly moving to be able to feed and to remove waste. A sponges body is covered with many pores called ostia that allow for the flow of water to enter the body. The pores lead to a system of canals where there are chambers lined with collared cells called choanocytes. The movement of a hair-like whip or flagellum in the cells is what forces water through the sponge. And these cells have a sticky collar which picks up the food particles. Another type of cell called an amebocyte then takes food to other cells in the body. The water and any waste end up in the central cavity of the animal and leaves through a chimney-like opening called the osculum.
They can control the flow of water by closing, fully or partially, the ostia or osculum openings and changing the speed of the flagella. They have the ability to shut everything up if there is too much sand or silt in the water.
Reproductively sponges can reproduce asexually by fragmentation regeneration, (a sponge can regenerate from a fragment of its body if the correct cells are present), budding or producing survival pods called gemmules. They also reproduce sexually and are hermaphroditic, some sources say that each time they spawn they will be either male or female but not both.
Are they important?
Sponges are a very important part of a marine ecosystem. They are very effective filter feeders and can capture even very small particles like bacteria which is one of the reasons why they are so interesting to scientists.
Sponges have been found to be able to remove up to 95% of bacteria and particles from the water and 90% of dissolved organic carbon so they process nutrients to make them more biologically available as food for other animals. They also seem to play a role for the recirculation of carbon, silicon, and nitrogen.
Fun Fact: A few species of sponge are carnivores and feed on prey such as small crustaceans.
An even funner fact: Dolphins have been seen to use sponges as a tool, to protect themselves when looking for food on the ocean floor.