Armored dinoflagellates of the Southwestern Atlantic Ocean




McKenzie, C.H.

Journal Title

Journal ISSN

Volume Title


Texas A&M University.


The armored dinoflagellates from net hauls taken from ARA/ISLAS ORCADAS cruises 17-78 and 19-79 were studied using light and scanning electron microscopy. the samples were taken at two different seasons, austral spring and fall, on similar cruise tracks. A list of armored dinoflagellates was compiled from twenty previous cruises in the research area. a survey was made at each of forty ISLAS ORCADAS stations to determine the relative number and species of dinoflagellates present. A total of sixty-four species were identified, including three possibly new species and three species not previously reported in the research area. Through scanning electron microscopic observations more information regarding thecal pores, surface texture, apical pores, cingular and sulcal lists and some cingular sulcal plates was detailed. Species diversity as determined by number of species was also recorded and found to be highest in the Drake Passage and at the more northern oceanic stations north of of South Georgia Island. Protoperidinium and Dinophysis had the most species diversity. Distribution of genera is plotted on a three-dimensional bar graph by station and season. Protoperidinium was the dominant genus particularly in the austral fall; it made up over 80% of the dinoflagellate community at several stations. Dinophysis and Ceratium were the second and third most common genus, respectively. Protoperidinium and Dinophysis were found at almost all stations, but the actual species varied with the region and season. Ceratium was found at the northern stations but was abruptly absent at the stations south of the Polar Front. The chi-square test was used to determine the independence of the genera in relation to the season and region. At a 0.05 alpha level, the species were independent of season, but not independent of region. A cluster analysis was used to find hierarchaical clusters of the stations according to the similarities in species content.


392 p., Dissertation


dinoflagellates, species diversity, seasonal distribution, Dinophysis sp., regions, cluster analysis, geographical distribution, genetics, collections