Efeitos de diferentes dimensões celulares na sedimentação de espécies fitoplanctônicas

Abstract

The mortality due to aging, parasitism and herbivory are causes of losses for all organisms. For phytoplankton settling, and water flow are also important. Settling is observed as the disappearance of cells from the top section or their arrival at the bottom of the water column. The prevalence of phytoplankton populations in the illuminated layers depends on the size and shape of the cell. The Stokes law stablish that the settling rate of a particle varies with the square of its radius. The objective of this study is to verify the influence of different dimensions on the settling rate of phytoplankton species. The hypothesis is that the dimension determine phytoplankton settling rate. It is expected that the ratio between surface area and biovolume affects the settling rate more strongly than each of these dimensions alone. We also hypothesize that this ratio could generate a greater predictability of phytoplankton settling rate. The experiments were performed in SETCOLs (settling columns), which allow determine the settling rate for cultivated species and other species obtained from a reservoir. After performing experiments, the organisms were quantified and measured to obtain their settling rates and different aspects of their size biovolume (V), surface area (S) and ratio S:V. The species settling rates were compared by one-way ANOVA, followed by a Tukey test. The dependence of settling rate in relation to cell dimensions was assessed by a linear regression analysis, generating predictive models to estimate settling rates. The adjustment between models and real data was verified by Pearson correlation analyses. The two models based on biovolume were the best predictors of the real settling rates of phytoplankton cultures and could be used to predict the settling of the species obtained in field samples.