Morphology and Ecology of Freshwater-blooming Durinskia baltica (Dinophyceae: Peridiniales) in Xochimilco, Mexico

Framework and Aims: A dinoflagellate identified as Durinskia baltica has caused early spring blooms since 2007 in a eutrophic freshwater channel system influenced by agriculture and livestock in central Mexico. The goals of this study were to document the morphology of this freshwater strain of D. baltica, and describe its bloom formation in relationship with local environmental conditions.

Study Design, Place and Duration: The species blooming in Xochimilco was identified through light and electron microscopy, recording cellular structures that distinguish it from other Dinophyceae. Environmental and climatic variables were monitored during one-year collections of biological material to document the ecology of the species.

Methodology: Biweekly and monthly surveys (September 2010 to January 2011 and fortnightly from February to August 2011) were conducted (calibrated field sensors and laboratory analysis) and population density of flagellate cells and cysts were performed (Sedgwick-Rafter chamber). For data analysis, descriptive statistics, correlations between variables and a Categorical Principal Components Analysis were performed.

Results: Morphological study of D. baltica revealed the typical plate 1a, sulcal plates, endosymbiont nucleus and stigma. Pearson correlations confirmed a significant relationship between flagellate cells and environmental temperature (P = .02) and pH (P = .003). Cysts were correlated with annual rainfall (P = .001). Total variance explained by the two-dimensional CATPCA (> 76%) model showed a strong association between the maximum and minimum species densities, with ambient conditions and trophic status indicating that nutrients, pH and climatic factors were parameters responsible for bloom formation and cyst occurrence.

Conclusions: D. baltica is indeed a freshwater species and is able to live at relatively high temperature in shallow, eutrophic columns. A seasonal effect and hence an association with temperature suggests that water bodies in urban-influenced tropical latitudes may be well suited as environments for D. balticablooms.