Abstract

This study present the phytoplankton assemblages from May 2006 to February 2015, based on samples monthly collected from 158 sites in Los Lagos (LL), Aysén (AY) and Magellan (MA) regions of Southern Chile. Phytoplankton analysis included species identification, estimation of cell density and bio-volume. In addition, the study includes the results from multivariate analysis on phytoplankton spatial changes and the relationship with environmental conditions. Diatoms were the major component, dominating the phytoplankton abundance at all sites, being the principal species Chaetoceros socialis, Pseudonitzschia cf. pseudodelicatissima and Chaetoceros debilis in the LL (13%), AY (13%) and MA (9%), respectively. Dinoflagellates acquire numerical relevance during summer at some sites located in the AY. We observed less frequent occurrence and low abundance of harmful dinoflagellate species in comparison to diatoms. Within this group, Alexandrium catenella showed high abundance (104 ~105 cells L-1) in the AY and the MA, with the highest values (1.2×106 cells L-1) detected near the Melinka zone in the AY during summer 2009 bloom. In biomass terms, A. catenella incremented its importance, reaching values ~5% for stations located in Moraleda channel (AY). All samples multivariate analysis showed that the phytoplankton assemblages responded to environmental variability and defined a different phytoplankton composition for each study region. Significant relationships between HABs species and environmental variables were found, being ~25% of HABs species variability explained by the water temperature. Baseline studies are relevant to determine future approaches to understand changes in species composition, occurrence and abundance of HABs associated to environmental conditions. event, associated to a lower rainfall, a declination of water runoff from river Baker, higher radiation and higher water temperatures, suggesting that salinity and water temperature exert an important role in the distribution and abundance of A. catenella in the study area.