LIFE HISTORY AND IN SITU GROWTH RATES OF ALEXANDRIUM TAYLORI (DINOPHYCEAE, PYRROPHYTA)

Alexandrium taylori Balech is a phototrophic marine dinoflagellate. It produced recurrent blooms during the summer months (July and August) of 1994 to 1997 in La Fosca beach (NW Mediterranean). In addition to a motile vegetative form, A. taylori had two benthic forms: temporary cysts and resting cysts. Temporary cysts were a temporally quiescent stage produced from the ecdysis of the vegetative cell in both natural populations and laboratory cultures. Temporary cysts may divide to form motile cells. Resting cysts had a thicker wall than the temporary cysts and had a red accumulation body. Gametes and planozygotes were also observed in laboratory cultures. Alexandrium taylori showed in situ diurnal vertical migration with an increase of vegetative cells in the water column in the morning through midday, with concentrations peaking in the afternoon followed by lower levels at night. Most vegetative cells lost their thecae and flagella, and with them their motility, turning into temporary cysts that settled in the early evening. The number of temporary cysts in the water column rose in the evening and at night. The temporary cysts gave rise to motile cells the following morning. Synthesis of DNA occurred in vegetative cells at night, and a preferential period of cell division occurred at sunrise. The estimated division rate in the field was 0.4–0.5 vegetative cells·day⁻¹. Temporary cysts had twice the DNA of a G₁ vegetative cell. The minimum in situ division rate of the temporary cysts was 0.14 day⁻¹. The role of the resting and temporary cyst population in the annual recurrence and maintenance of the A. taylori bloom is discussed.     

IMMUNOFLUORESCENCE FOR AUTECOLOGICAL STUDY OF A UNICELLULAR BLUEGREEN ALGA12

Fluorescent antibody (FA) preparations were developed and tested as an approach to recognition and enumeration of a specific unicellular bluegreen alga in a natural ecosystem. Antibodies made against an axenic culture of Synechococcus cedrorum Näg. gave a high agglutination titer and an excellent homologous staining reaction. Antibody specificity was tested with 28 heterologous cultures of bluegreen algae, known cultures of chemoautotrophic bacteria and heterotrophic bacteria, and randomly selected unknown bacteria from soil, sewage and aquatic habitats. FA staining of bluegreen algae was restricted to S. cedrorum and six heterologous isolates, all indistinguishable microscopically from S. cedrorum. The ability to enumerate S. cedrorum FA-reactive cells in nature was demonstrated with data on population densities for samples taken from water columns of stratified holomictic lakes in northcentral Minnesota.