Xestospongia muta
| Giant barrel sponge | |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Porifera |
| Class: | Demospongiae |
| Order: | Haplosclerida |
| Family: | Petrosiidae |
| Genus: | Xestospongia |
| Species: | X. muta |
| Binomial name | |
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Xestospongia muta (Schmidt, 1870) |
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The giant barrel sponge (Xestospongia muta) is the largest species of sponge found growing on Caribbean coral reefs. It is common at depths greater than 10 metres (33 ft) down to 120 metres (390 ft) and can reach a diameter of 1.8 metres (6 feet). It is typically brownish-red to brownish-gray in color, with a hard or stony texture. The giant barrel sponge has been called the "redwood of the reef" because of its size and estimated lifespan of hundreds to a thousand or more years. It is perhaps the best-studied species of sponge in the sea; a population on Conch Reef, in the Florida Keys, has been monitored and studied since 1997.
The giant barrel sponge is variable in form. It is very large and firm. Typically it is barrel-shaped, with a cone-shaped cavity at the apex known as the osculum. However, some individuals within the same population may be low and squat or relatively tall and thin. Similarly, the surface can range from smooth to rough, rugged, and irregular, sometimes with buttresses. In shallow water the color is brownish-red to brownish-gray, but at greater depths and in caves and under-hangs, or when the sponge is undergoing cyclic bleaching events, the sponge is pinkish or white.
The giant barrel sponge is common on reefs throughout the Caribbean Sea, the Bahamas, Bermuda and the reefs and hard-bottom areas of Florida and the Gulf of Mexico. In terms of benthic surface coverage, it is the second most abundant sponge on reefs in the Caribbean region. On the reefs off the Florida Keys, it may be as common at two individuals per square metre (yard), and the total biomass of the sponge is greater than any other benthic invertebrate. The sponge grows on any hard surface; the smallest individuals observed are about 1 cm. Two or more closely related species that are visually indistinguishable from X. muta are found on reefs in the Pacific and Indian Oceans (particularly Xestospongia testudinaria).
The giant barrel sponge is a filter feeder. Water is continually pumped into the sides of the sponge, through the sponge body. and out the osculum at the top of the sponge. Small pores in the sponge body are connected to channels lined by collar cells, each with a flagellum, and the beating of these flagellae draws water through the channels. Incoming particles, particularly microscopic bacteria and prochlorophytes, are phagocytosed by the collar cells. Sponges like X. muta also absorb dissolved organic compounds directly from the seawater as part of their diet.
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Wikipedia