Since 1979 has been reported harmful microalgae blooms (HAB) on the Pacific coast of Costa Rica, it was identified until 2005 at least 13 taxa of dinoflagellates. In recent years these phenomena have intensified both spatially and temporarily, discolorations occur almost uninterrupted; they are distributed for months and which extend along the coast causing death fish and smelly in the water. Such massive FAN started with Pyrodinium bahamense, whose discoloration in 2000 lasted for more than one year and in which morphotypes were observed the two varieties of the species, coexisting alongside with Gymnodinium catenatum and causing serious cases of paralytic shellfish poisoning by seafood consumption (PSP. Later, from September 2003 until June 2004, Cochlodinium cf. polykrikoides produced discolorations in the entire Pacific coast followed by extensive stains of Akasiwo sanguinea and Gymnodinium instriatum. The latest event was observed in June 2005 when Alexandrium monilatum produced extensive discolorations with chains formed by more than 100 cells. The HAB of dinoflagellates are now common along the coasts of Costa Rica, possibly as a result of the current environmental conditions that favor the massive proliferation of invasive species (aggressive), which can even affect other sites in the American Pacific as the case of P bahamense var. compressum which can be moved towards Mexico along the Central Pacific Coast through the Costa Rica Current Flow and Mexican Western Current.
