The influence of environmental conditions on the morphologicalvariability of phytoplankton in an oligo-mesotrophic Turkish lake

Abstract

Phytoplankton dynamics and morphological plasticity were studied in an oligo-mesotrophic lake from late spring to earlyautumn in 2004 on a weekly to bi-weekly basis. This study aimed to evaluate the effect of environmental constraints on morphologicalplasticity and size structure of dominant species through the stratified period of the lake. While centric diatoms developedmainly in the epilimnion, Fragilaria crotonensis, Synedra sp. and Synedra acus were very well distributed through thewhole water column, as was the cryptophyte Plagioselmis nannoplanctica. A filamentous cyanobacterium, Planktothrix rubescens,was stratified in the metalimnion throughout the sampling period, while Mougeotia sp. was entrained through the wholewater column during the early autumn. Surface area / volume (S/V) ratios were calculated for the dominant species on each samplingdate. The minimum S/V ratio was found with centric diatoms, while maximal values measured were for Synedra sp. andAsterionella formosa. The S/V ratio of the only dominant cryptophyte, Plagioselmis nannoplanctica was also high; variationswere negatively correlated with NO3-N and PO4-P (-0.62 and -0.61, respectively) and positively correlated with euphotic depth(r=0.57) and temperature (r=0.82). On the other hand, the S/V ratios of Fragilaria crotonensis and Cyclotella ocellata each showedstrong negative correlation with silica concentrations (-0.55 and -0.62, respectively). It is concluded that allometric relationshipsshowed significant differences among species according to depth and season.