The vast majority of sponges are colorful, easy to keep when healthy and correctly transplanted, readily available and inexpensive. While they traditionally haven’t been a mainstay of aquarist tanks as they are stationary and are perhaps not as exciting as active swimming, they do have a certain appeal. Sponges are incredibly interesting species and that provide a great educational addition to a tank and really accentuate an aquarium reef with a much-needed pop of color.
There are over 8,500 recognized species of sponges across the world. Yet scientists believe there are actually more like 25,000 species in the ocean. Only a fraction of these species are kept by aquarists as generally sponges can be very delicate so sensitive to changes in water parameters so can not be successfully transplanted or kept. There are also other reasons why many species are not suitable for aquaria: some come from deep-water locales that make it difficult to transplant a specimen, others can cause painful skin reactions in humans, other species will attack, eat or even kill corals, and some grow so slowly that it would be akin to harvesting a redwood tree (scientists have aged the largest known Caribbean barrel sponges, Xestospongia muta, which almost provide underwater caves large enough for scuba divers to disappear into, at more than 2,000 years old).
What Exactly Are Sponges?
Sponges are the simplest of all multicellular animals currently known. They lack any sort of tissues or organs that you normally associate with living animals, making them look deceptively more like a plant. Instead, they are a collection of a few different types of cells living together in a highly specialized and organized mass. What is incredibly interesting about this degree of organization is that you could put a sponge through a blender and it would not die, in fact it would slowly begin to regenerate and reconstruct itself (water this video here; DO NOT TRY THIS). During their adult life, they attach themselves to the bottom of the seafloor and the majority of species will stay there for the entirety of their life, with the exception of a few that can slowly move by rearranging the placement of their cells.
Sponges get their energy through filter feeding. Their ‘body’ provides a sieve-like structure that strains tiny food particles from the water, using specialized types of cells called choanocytes, which are commonly known as collar cells. Each collar cell starts with a round ball within the sponge, and these round cells line-up side by side around the edge of the sponge. Then each round cell has a collar, similar looking to a dog’s collar, which has a tail-like structure protruding out of it known as a flagellum. When all these tail-like flagellums are lined up in their thousands, it creates a water current to allow water (and food particles carried in it) to pass through the sponge structure.
As fellow animals, sponges are family. Humans and sponges both descended from a common ancestor. But no matter how unlike humans they are, we actually have a lot more in common than you might think. Scientists have found that we both share the same type of gene regulation. This is the process of turning genes on and off, this is essentially a toolkit within our bodies that makes a cell decide to become a red blood cell or a muscle cell for example.
The Orange Fan Sponge
The orange fan sponge (Axinella polycapella) is a beautiful, brightly colored and, unsurprisingly, an orange sponge. This sponge has a smooth to velvet surface with tiny pores less than 1 mm in diameter. It naturally occurs in patches of rock or coral reef at depths between 13 and 44 m. This sessile species is found in the tropical waters of the Western Central Atlantic.
It is an especially tough and adaptable sponge, which is great for beginner aquarists to try their hand at. The orange fan sponge requires a strong water current, moderate lighting and supplemental feeding. This fan sponge feeds on bacteria that it filters from the moving water. As will all sponges, it is important not expose sponges to the air.
MINIMUM TANK SIZE: 60 gallons
DIET: Filter Feeder
CARE LEVEL: Moderately Easy
REEF SAFE: Yes
WATER CONDITIONS: 72-78° F, dKH 8-12, pH 8.1-8.4
How To Care For Your Sponges
Whilst there are lots of easy to care for species, we recommend you start small. Research which sponge you would like to keep too, this will really help provide you with the tools needed for success. Things to find out include where it comes from, what environment it is naturally found in, whether it has any symbiotic relationships with other species, how big it will likely grow, and if it produces any toxins that are harmful to humans (as some do). The more you know in the beginning, the greater your chances for success.
In general, the best kind of aquarium set is a deep sand bed with lots of life and refugium. We don’t recommend putting them in a reef aquarium unless you are more experienced. Your sponge will need adequate filtration and water movement, otherwise it will starve. You can help make sure your sponge gets enough food by providing supplemental meals of marine snow, phytoplankton and zooplankton. Stirring the aquarium substrate once in a while to release food particles into the water may also be helpful.
As with any new addition, it is important to acclimate them slowly. Any new sponge must be slowly acclimated to your aquarium, preferably in a quarantine tank on its own. You can very carefully put it in a container with the water it came in into the quarantine tank and then use the Drip Method to slowly drip water from your main tank into the container. Using the Drip Method is recommended as it is slower and gives the sponge time to adjust carefully.