Spatial and seasonal changes in the species composition of armored dinoflagellates in the Southwestern Atlantic Ocean

Summary To compare the spatial and temporal (seasonal) distribution of dinoflagellates, vertical net hauls were taken along similar cruise tracks in the Scotia Sea, Weddell Sea and across the Polar Front Zone in the austral spring and the austral fall. Sixty-three species of armored dinoflagellates were identified and enumerated. Chisquare and hierarchical cluster analyses were performed to define spatial and seasonal patterns in genera and species assemblages. The dominant genera were Protoperidinium, Dinophysis and Ceratium. The Polar Front Zone was an important biogeographical barrier with Blepharocysta, Gonyaulax, Heteroschisma, Oxytoxum and Podolampas occurring mainly north of the Front. Species found primarily in the austral spring were Ceratium fusus, Ceratium lineatum, Dinophysis antarctica, Dinophysis simplex, Gonyaulax digitale, Protoperidinium pyriforme and Protoperidinium variegatum. Austral fall species included Dinophysis tuberculata and Protoperidinium elegantissum. Distribution of armored dinoflagellates in the Southwestern Atlantic Ocean is influenced at the generic level by spatial considerations, particular with relation to the Polar Front Zone, whereas species composition can be effected by both region and season.