Adventures in Symbiosis

A research adventure is described in which the symbiosis ofHydra and Chlorella is modeled with a novel computer program.The model faithfully simulates equilibrium populations of hydraand algae, and is used to discern the parameters which governthe stability of the symbiosis and its breakdown resulting fromeutrophication. The model reveals that amelioration of a nutrientlimitation causes symbiotic Chlorella to reduce fitness of hostcells, converting a stable mutualistic symbiosis into an unstableparasitic one.