The effect of environmental factors on the growth and size structure of two dominant phytoplankton species in Büyükçekmece Reservoir (İstanbul, Turkey)

Bu çalışmanın amacı Büyükçekmece Gölü’nde kaydedilen dominant fitoplankton türlerinin yoğunluk ve boyutlarında meydana gelen mevsimsel değişimi görmek ve bu değişimde etkili olan çevresel faktörleri ortaya koymaktır. Araştırma süresi boyunca gölde sekiz farklı algal divizyoya ait toplam 78 taxa teşhis edilmiştir. Bacillariophyta ve Chlorophyta en çok tür sayısına sahip divizyolar olarak bulunurken, Cryptophyta divizyosundan Plagioselmis nannoplanctica (Skuja) Novarino, Lucas et Morrall ve Cryptomonas sp. yoğunluk ve biyokütle bakımından oldukça yüksek sayılara ulaşmışlardır. P. nannoplanctica toplam fitoplankton biyokütlesine katkıda bulunan başlıca tür olarak kaydedilmiştir. Kış döneminden ilkbahar başına kadar ve yaz dönemi arasında ölçülen Plagioselmis türünün hacimleri arasında belirgin farklılık kaydedilmiştir. Türün yapısal büyüklük ve bolluk derecesinin mevsimsel değişimi arasında önemli negatif ilişki bulunmuştur. Çalışma süresi boyunca besin tuzu değerlerinin yüksek olarak kaydedildiği kış döneminde P. nannoplanctica en yüksek (boy: 17,5 μm and çap: 10 μm; biyohacim: 589,5 $mu m^3$) hücre boyutuna sahip olurken, birey sayısı bakımından çok düşük (< 6 cells × $10^{3} {1}^{-1}$) değerler bulunmuştur. Bu dönemde, en düşük yüzey-hacim oranı (SA/V: 0,87) bulunmuştur. Ölçülen çevresel faktörler arasında yalnızca su sıcaklığının istatistiksel olarak P. nannoplanctica hücre boyutu ile önemli negatif ilişkisi ($R^2$:0,635; P < 0,01) kaydedilmiştir. Çalışma sonucunda elde edilen bulgular cryptomonadların

Büyükçekmece Gölü’nde (İstanbul, Türkiye) baskın olarak kaydedilen iki fitoplankton türünün gelişimi ve boyutları üzerine çevresel faktörlerin etkisi

The aim of this study was to investigate seasonal variability in the growth and size structure of dominant phytoplankton species in Büyükçekmece Reservoir, and to determine the environmental factors that affect morphological plasticity in those dominant species. In total, 78 taxa from 8 algal divisions were identified. Bacillariophyta and Chlorophyta were 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 was the major contributor of biomass in the reservoir. A significant difference in Plagioselmis species biovolume was observed between winter-early spring and summer. A significant negative correlation was observed between its seasonal size structure and 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: 589.5 $mu m^3$), but its abundance was very low (< 6 cells × $10^{3} {1}^{-1}$). The minimum surface:volume ratio (SA/V: 0.87) was recorded in this period. Among the measured environmental factors, water temperature was the only parameter that had a statistically significant negative relationship ($R^2$: 0.635; P < 0.01) with P. nannoplanctica cell size. The results indicate that seasonal changes in cryptomonad size structure were controlled by water temperature.

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