Crabs are not filter feeders, so they don't have as many toxins as other species of shellfish. However, crabs sometimes contain bacteria such as V. cholerae, which can cause food poisoning. In addition, crabs harvested from polluted water may contain traces of mercury, dioxins or polychlorinated biphenyls.
"Red tides" refer to red or brown patches of color that indicate the presence of certain microorganisms in the water. Some people believe red tides indicate harmful toxins, but toxins may be present in the water whether or not the water appears discolored.
Clean crabs carefully before cooking them and always boil crabs thoroughly. Do not eat raw crabs. Do not eat the internal organs of crabs, which are sometimes referred to as "crab butter." Do not harvest crabs on beaches closed for pollution or high biotoxin levels.