Pfiesteria is a single-celled planktonic creature (neither a true animal or plant). Billions lie dormant on the sea bed. In response to a chemical released naturally by fish, the pfiesteria develop sperm-like tails and swim towards the fish, which they kill or stun by releasing toxins. Changing shape again, the plankton develop a straw-like device by which they attach themselves to the fish and suck up its flesh.
Pfiesteria for red tides, up to six kilometres long, killing millions of fish at a time. Fishermen have suffered memory loss and developed open sores by breathing near the plankton: one California laboratory researching its effects on humans had to be shut down when researchers developed mysterious illnesses. There is no cure for the effects of pfiesteria.