Parasitic worms can pose a serious threat to the Dungeness crab, a commercially important fishery species found along the west coast of North America. The worms are thought to have caused or contributed to the crash of the crab fishery of central California during the last half century. New research shows that infected crabs can rid themselves of parasites by moving into the less salty water of estuaries. Low salinity kills the worms creating a parasite refuge for the crabs....