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The Amazing Barrel Sponge

Updated on March 7, 2013
A cluster of Barrel Sponges
A cluster of Barrel Sponges | Source

The redwood of the ocean

Underneath the rolling waves of the ocean’s surface zone, a diver explores a diverse coral reef. Many exotically colored fish highlight the landscape, darting past in pursuit of a meal, or in escape of becoming one. Some hide in the shadows and nooks, while others flaunt their colors in order to attract mates. The reef itself is a wild formation. Various types and shapes of corals mound over the seabed in places where the light, filtering down through the water, is bright and nourishing. Many other organisms live among the coral, growing out through gaps in the rock or growing independently, often playing host to fishes and other members of sea life. The diver swims above the reef. He spots a towering shape in the distance and swims closer to discover, nestled down in a bed of sea grass, a plant-like creature of immense size. Its body towers above the reef, porous and shaped like a huge barrel. Its orange exterior is not smooth, but thick-walled with prominent ridges. The edge of the cup, although wide enough to engulf the diver’s body, is irregular and indented at random intervals, like the edge of a recklessly ripped paper. Looking in through the opening, the diver sees a skinny, orange fish swimming idly within the cavernous center, as though hiding out. The center cavity is large enough to fit the diver himself, although he knows enough about the delicate balance of reef organisms not to attempt it.

The diver’s discovery was actually a Barrel Sponge (Xestospongia Muta) and although its texture and appearance would suggest, it is not a plant, but an animal. However, to fully understand and appreciate the Barrel Sponge in its entirety a person must also look at sponges in general.

There are about 5000 species of Sponges worldwide, most of them from marine environments, but there are around 150 species adapted to freshwater 1. “For centuries, sponges were thought to be plants, the nests of ‘sea insects,’ or even solidified sea foam....Late in the eighteenth century an Englishman, John Ellis, noticed how sponges pull water into themselves and squirt it out in jets through openings in their bodies. He demonstrated that sponges belong to the animal kingdom, but as late as 1841 at least one respected scientist still claimed they were plants,” (Silverberg, 1972).

Sponge Anatomy and Feeding Habits:

The sponge is unique to other animals in that it does not have many of the same physical characteristics that most other animals have. With no digestive track, muscles, tissues, blood, heart, or nervous system among other things, a sponge is more simply an assortment of different cells with different functions 2. "These cells do not organize in such a way as to form a body, skin, or tissues, but are more of a “loose aggregation of different kinds of cells”1. Water passes through a layered system of holes, or pores 3. These lead to chambers, all lined with ‘collar cells’, the tops of which are funnel shaped, where minute appendages, called ‘flagellum’ hang and beat back and forth, forcing water inside the sponge. Through the stream of water, food and oxygen pass through the sponge along with bacteria, plankton, and detritus particles, which sponges use for nourishment. The sponge absorbs the nutrients and oxygen, while filtering out the carbon monoxide and harmful wastes. Still other cells called “amebocytes” transport these filtered nutrients further inside the sponge 3.

Colors, Shapes, and Sizes:

Sea Sponges come in a variety of shapes, sizes and colors. Orange, blue, gray, convoluted, upstanding, bulbous or narrow are a few of the variations. The shape and color of any type of sponge may vary a lot according to environmental factors such as wave action, light exposure, and water currents. Most sponges only grow to be a few centimeters in height, but there are other species that bulge to a height of over six feet, and that is where we find, specifically, the Barrel Sponge .

Barrel Sponge Spawning

Sponge Reproduction:

Sponges are hermaphrodites, meaning that a single sponge is of both separate sexes. Because of this, sponges and can become male or female as the situation requires, however, they do not fertilize their own eggs with their own sperm. Sexual reproduction begins when the sponge releases male gametes into the water and it is then pulled into the pore systems of its neighboring sponges in the same way as they take in food items, through collar cells. “The spermatozoa are ‘captured’ by collar cells, which then lose their collars and transform into specialized, amoeba-like calls that carry the spermatozoa to the eggs. In most sponges for which developmental patterns are known, the fertilized egg develops into a blastula, which is released into the water (in some species, release takes place right after fertilization; in others, it is delayed and some development takes place within the parent),” 1. After a few days of floating, the baby sponges (which look somewhat like plankton) attach themselves to a hard surface and start growing 1. Barrel Sponges reproduce sexually, and mass release of the gametes takes place in September, after which fertilization occurs in the seawater.

Sponges may live anywhere from a few months to twenty years or more depending on the availability of nutrients, sea floor trawling, and other factors that might negatively affect a sponge’s life span.

How Much Water Can a Sponge Pump?

Since sponges are filter feeders, meaning that they get their food and nourishment from filtering water, the amount of water that goes through them is vital to the amount of nourishment they receive. This amount of water filtered through even the smallest sponge is phenomenal. It is a continuous cycle of water coming in, and water spewing out. Sponges are never at rest, and never cease pulling in water until they die. “How much water a sponge filters depends on the area of a sponge’s oscula (outlet) multiplied by its pumping velocity....For example, if the outlet pumping speed is 10cm/sec. and the radius of the sponge’s osculum is 22cm, the volume [of water] pumped per second would be 15.2 liters,” 4. As a person can imagine, a Barrel Sponge, with its gigantic proportions and wide radius of osculum, would pump an unbelievable amount of water every day! In order to take in enough food to gain one ounce, a sponge must draw one ton of water through its body (Silverberg, 1972). “Coral reef scientists estimate that every 36-48 hours, all of the water on a coral reef passes through the body of a sponge somewhere,” 4.

Where Are Sponges Found?

Sponges are ubiquitous, found in virtually all aquatic habitats and at all latitudes of every ocean in the world, although they are most common and diverse in the marine environment 1. Also, they can be found at all depths from the inter-tidal to the deep-sea. Most of the large sponges such as the Barrel Sponge come from the tropics while sponges that live in tide pools and in temperate climates are typically smaller than those in the open sea. Barrel Sponges can be found from the Western and Central Indian Ocean, Into Malaysia, northeastern Australia, and New Caledonia 5.

Types of Sponges:

Unlike most animals, which move through their habitat, sponges are immobile [sessile], living attached to solid surfaces,” (Burnie, 2001). There are two types of sponges, freestanding, and encrusting. Encrusting sponges are similar to moss because they tend to cover the surfaces of rocks. They are not very tall, or remarkable in shape, and their inner volume is much less than their surface area. Freestanding sponges, on the other hand, have lots of inner volume compared with their surface area 2. They grow into strange shapes and gigantic sizes. Barrel sponges are freestanding sponges, and make their habitats in reefs and Lagoons, on rock or dead coral substrates 5.

Final Thoughts:

Sponges have many uses—from their roles in keeping the balance of biological processes in their habitats, to uses as common bath sponges and ingredients for medicines. But one thing they will always remain is a unique and impressive oceanic treasure for Divers to enjoy. They make the deep oceans and reefs of this world more interesting, and add a little more variety to the waters. As for the Barrel Sponge, its nickname, “redwood of the ocean” proves that it will always capture the eyes and imaginations of those who are lucky enough to come upon them.


For simplicity sake, and not to interrupt the text too much, I entered my web sources as links, and referred back to them as I went along. If you wish to check up on the information contained here, click on the active links 1-9 and they will take you to the websites that I gleaned from. Here are the book resources:


Burnie, David ed. 2001. Animal. Dorling Kindersley, London. 528 pp.

Silverberg, Robert. 1972. The World Within The Tide Pool. Weybright and Talley, New York. 39 pp.


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