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BackgroundThe most common sponge in the Chesapeake Bay looks nothing like the kind you use to scrub the bathtub (or that sponge in the square pants who lives in a pineapple under the sea). On the contrary, Microciona prolifera, the red beard sponge, is a brilliant orange or red spreading encrustation that grows in small clumps to nearly a foot in diameter, with fingerlike branches and miniscule pores. Despite its apparently simple structure, the red beard sponge, like its relatives, is actually a dense colony of cooperating cells that perform specific functions for the organism's survival.
The phylum of sponges, the Porifera, is divided into three classes: the Calcispongaie, sponges with limy spicules; the Hyalospongaie, or glass sponges; and finally the largest class of sponges, the Demospongaie, to which the red beard sponge belongs. While thousands of species of these sessile, long-lived organisms are known to exist, only about 20 live in fresh water. Few species other than the red beard thrive in the Bay's brackish waters. All sponges have porous exteriors or "skeletons" of fibrous material that may be calcareous, siliceous or, as in the case of the red beard sponge, made of a tough protein called spongin. A sponge's surface structure contains pores, or ostia. Water and food particles enter the sponge through the ostia and a system of canals into chambers that are lined with cells containing sticky, collar-shaped structures, through which extends a beating, hairlike flagellum. The current created by the flagellum's beating drives the water through the canals and out of the sponge through the osculum, a larger opening through which waste products leave the organism. A constant supply of water is necessary for the sponge to function. Most sponges grow subtidally or in the low intertidal zone. Many sponges have chemical defense mechanisms that help protect them against certain bacteria; they produce toxins or unpleasant tastes and odors that ward off predators or prevent coral overgrowth that could threaten the sponge's osculum or other systems. Some sponges are a little more aggressive, such as the burrowing sponge, which digs into live mollusks or corals.
Like others in this phylum, the red beard sponge reproduces both asexually and sexually. If its branches are damaged or broken off, the remaining fragments can regenerate or bud into complete sponges. The species was one of the first organisms found to reorganize its form after its cells had been experimentally separated. When the sponge is squeezed through a fine screen into a bowl of water, the cells in the bowl begin to move toward one another, where they adhere and begin to form a new sponge. The red beard also reproduces sexually and can release clouds of sperm into the water to fertilize the egg cells of another sponge. Wave action and the movement of flagella facilitate this process and also propel fertilized larvae out of the parent organism, where they may settle and attach to a surface and develop into a sponge. The red beard sponge's range extends from Nova Scotia to Florida and Texas, and in the West from Washington to California. In the Bay it grows below the low-tide line on rocks and pilings, oyster shells, and other firm objects. Its spongin structure also creates habitat for other Bay creatures, including worms, small mud crabs, shrimp, small fish such as blennies and other juvenile fish species.
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