Biologists often fail to recognize the importance of a species to an ecosystem until that species is no longer present in the ecosystem. A case in point is that of the long-spined sea urchin, Dindema antillarum. Scientists and fishermen long considered the sea urchin a spiky pest that served no useful purpose; recreational divers would even feed sea urchins to fish just for fun. The last 20 years, however, have proven that the sea urchin does indeed playa valuable role in the marine environment. 　　Sea urchins are members of the phylum Echinodermata, the category of invertebrate animals with spiny exterior shells, which also includes starfish, brittle stars, and sand dollars. Sea urchins have a spherical body contained in a hard shell that is covered with long sharp spines. They walk around on shorter spines located on the underside of their bodies. A sea urchin's mouth is also located on its underside; this mouth is a five-toothed structure called Aristotle's Lantern, adapted to scraping algae and organic matter from rocks and corals. Sea urchins eat a vast amount of algae. 　　Exactly how much algae they consume has become clearer in the past two decades because urchins have virtually disappeared from many Atlantic environments. In 1983 a barge traveled from the Pacific to the Atlantic through the Panama Canal carrying a bacterium that proved devastating to the sea urchin population. Nearly all long-spined urchins in the tropical western Atlantic died as a result of this exposure. Without sea urchins to eat the algae, aquatic greenery grows out of control. It has completely covered some coral reefs - in Jamaica, before the sea urchins died off, algae covered just 1 percent of shallow reefs, but two years after the plague it covered nearly 95 percent of shallow coral. 　　Many reefs in the Bahamas have abruptly transformed from multicolored undersea wonderlands into monochromatic mossy-looking hillocks. Coral that is covered by algae quickly dies, unable to receive necessary sunlight and nutrients from the water. The algae cover also makes it difficult for both corals and sea urchins to breed, because their larvae cannot find a clean surface on which to anchor. 　　Scientists have completely changed their views of sea urchins from that of the early 1980s. Sea urchins are one of the first organisms to show signs of stress when water quality is bad, so the Environmental Protection Agency has begun monitoring sea urchins as an indicator of water conditions. Other scientists have taken on the task of redistributing the remaining sea urchins to endangered coral reefs. They hope that the sea urchins will clean off the reefs and make it possible for both coral and sea urchins to breed successfully and restore the marine environment to its healthy state.