In response to increased sunlight and temperature in the spring, the cysts germinate into free-swimming cells, which reproduce by cell division. If water conditions are good, the cells continue to divide, and growth is exponential a single cell can result in the reproduction of several hundred cells in just a few weeks. If other single cells are reproducing in a similar manner, this large bloom can result in shellfish toxicity. Paralytic Shellfish Poisoning, or PSP, is a life-threatening syndrome, and the onset of symptoms is rapid, usually within two hours of consumption. Symptoms include tingling, burning, numbness, drowsiness, incoherent speech, and respiratory paralysis.
Duration of effects is a few days in non-lethal cases.
The most severe cases result in respiratory arrest within 24 hours of consumption of the toxic shellfish. If the patient is not breathing or if a pulse is not detected, artificial respiration and CPR may be needed as first aid. Although there is no antidote, supportive therapy and treatment is usually adequate, and survivors recover fully. PSP monitoring in New Hampshire has been ongoing for several years. The weekly testing is performed on samples of mussels from April through the end of October, the period when the phytoplankton may be active.