The effect of environmental factors on the growth andsize structure of two dominant phytoplankton species inBuyukcekmece Reservoir (Istanbul, Turkey)

摘要

The aim of this study was to investigate seasonal variability in the growth and size structure of dominantphytoplankton species in Buyukcekmece Reservoir, and to determine the environmental factors that affect morphologicalplasticity in those dominant species. In total, 78 taxa from 8 algal divisions were identified. Bacillariophyta and Chlorophytawere the most important divisions with respect to species number, but cryptomonads Plagioselmis nannoplanctica (Skuja)Novarino, Lucas, and Morrall, and a Cryptomonas sp. were dominant in terms of density and biomass. P. nannoplanctica wasthe major contributor of biomass in the reservoir. A significant difference in Plagioselmis species biovolume was observedbetween winter-early spring and summer. A significant negative correlation was observed between its seasonal size structureand abundance. During winter (December 2004-April 2005) nutrient values were higher than during autumn (October-Novermber 2005) and P nannoplanctica had maximum cell size (17.5 μm x 10 μm; biovolume: 589.5μm~3), but its abundancewas very low (< 6 cells × 10~3l~(-1)). The minimum surface:volume ratio (SA/V: 0.87) was recorded in this period. Among themeasured environmental factors, water temperature was the only parameter that had a statistically significant negativerelationship (R~2:0.635; P < 0.01) withP. nannoplancticacell size. The results indicate that seasonal changes in cryptomonadsize structure were controlled by water temperature.