engleski

Functional classification of diatoms in relation to oligotrophic environment in two deep karstic lakes

Phytoplankton in two deep karstic lakes Visovac and Vransko was sampled monthly from April to September 2009 and 2010, respectively, in the euphotic zone at the deepest part of the lakes. Chemical data were collected simultaneously with phytoplankton samples and statistical analyses have been utilized to address the question of diversity and succession patterns. Phytoplankton biomass was studied in the context of functional groups. To construct the comprehensive picture of phytoplankton distribution along the karstic area, phytoplankton biomass and its relation to assemblages of other deep karstic lakes in Croatia were also examined. Co-occurrence of phytoplankton assemblages dominated by diatoms, chrysophytes and dinoflagellates was observed and analyses confirmed that these common taxa reflect oligo-mesotrophic conditions of the habitat. Functional groups B (A), E and LO co- occurred in 50-90% of samples for both investigated habitats. Those three functionally well- adapted groups interchange in dominance during seasonal cycle and, thus, likely tolerate the constraining conditions of nutrients deficiency more successfully as an aggregated group. The fact that three groups describe such high percentage of phytoplankton community variation additionally accentuates the importance and applicability of functional groups. However, aggregating species into groups can provide only selective information about assemblage, so special attention was given to species belonging to functional group A and B. For identification to species level, diatoms of group A and B were studied from a precleaned material using light and SEM microscope. Their detailed taxonomical position and functional traits, as well as classification into coda A and B, were discussed for better description of those two groups in deep karstic oligotrophic lakes.

diatom ; karstic lakes ; oligotrophic lakes ; SEM

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