Pyrodinium bahamense, considered the sister taxon to
Alexandrium, is a tropical photosynthetic
euryhaline species of
dinoflagellates found mainly in the Atlantic Ocean. It is found in marine waters that have more than 20 psu of
salinity and are warmer than . The optimal salinity is considered to be around 35
psu and the optimum temperature is . However, regions where large cell densities of
Pyrodinium are found are usually shallow and have varied salinities and long water residence times. It was initially widely believed that the
compressum variety was toxic and found in the Pacific while the
bahamense variety was nontoxic and found in the Atlantic, but a 1972 toxic
algal bloom of
Pyrodinium bahamense in Papua New Guinea showed this was not the case. It is now known that
P. bahamense is a major cause of seafood toxicity and
paralytic shellfish poisoning, especially in Southeast Asia, and causes toxicity along Central American coasts. In addition, there are at least two places in the world where both varieties of
Pyrodinium bahamense are found together: the
Persian Gulf and coast of Mexico. The bright cobalt blue light produced by these dinoflagellates when they are mechanically disturbed creates a magical effect that draws many tourists to the bays. Most of the bays are in reserves, and no swimming is allowed, but guests are able to kayak in the bays at night with local guides to observe the bioluminescence. == Morphology and anatomy ==