First report of parasitism on the toxic dinoflagellate Alexandrium minutumHalim

Blooms of the toxic red tide phytoplankton Alexandrium minutum Halim (Dinop hyceae) have frequently occurred during recent years in the estuaries of no rthern Brittany, France. Some months after a bloom in the Penze River in 19 97, many Alexandrium cells in samples maintained in the dark at 14 degrees C were observed to be infected by the sporocysts of an unknown parasite, wh ich, upon exposure to increased light intensity and temperature, ejected ma ny small biflagellate zoospores. The parasite was found to infect laborator y cultures of several other dinoflagellate species, and estimates of parasi te-induced mortality indicate that this parasite is capable of removing a s ignificant fraction of dinoflagellate biomass in a short time, raising the possibility of its use as a biological control agent of toxic dinoflagellat e blooms. The effect of this parasite on natural A. minutum populations rem ains, however, to be estimated. This paper presents video images used in a preliminary identification and life cycle elucidation of the parasite, whic h may be affiliated with the Apicomplexan complex. (C) 2000 Academic Press.