Abstract

Alexandrium catenella is a dinoflagellate that produces Paralytic Shellfish Poison (PSP). It is widely distributed in coastal waters around the world, and forms large devastating blooms in southern Chile. Several strains were collected from Magellanic fjords and channels to study its life cycle and to assess its growth rate at various levels of salinity. Compared with field-collected cells, vegetative cells cultured in the laboratory were smaller, rounder, and formed shorter chains. Pellicle cysts formed rapidly under stress conditions when observed on microscope. This type of cyst was found in the gut of shellfish collected in the field. The sexual life cycle included isogametes that formed a large planozygote, which formed into a thick-walled resting cyst. All stages presented minor morphological differences compared with others closely related species in the genus. Formation of gametes was mainly restricted to the stationary phase of growth, and was probably induced by nutrient depletion. The maximum growth rate attained in cultures simulating summertime water conditions (i.e., 11