Also, says Graham, "Jellyfish play unique metabolic tricks" -- tricks that favor their survival in polluted waters like those of the gulf. The creatures are more than 95 percent water. (Humans are 65 percent water.) Dissolved within their fluid tissues is oxygen that fuels them when they enter the infamous Dead Zone -- 7,000 square miles of the Gulf of Mexico that becomes oxygen-starved during the summer. In the Dead Zone, oxygen is consumed by the decay of massive algae blooms, which are fertilized by the tons of fertilizer, sewage, and animal waste that continuously wash into the gulf, primarily from the Mississippi and Atchafalaya rivers. Most creatures, such as fish, shrimp, and crabs, either flee the Dead Zone or suffocate. But jellyfish, equipped with their built-in oxygen supplies, thrive in the Dead Zone and banquet on the ubiquitous plankton.