Morphology and physico-ecology of two rare freshwater epilithic diatoms: Hydrosera whampoensis and Pleurosira laevis

We isolated two rare centric diatoms, Hydrosera whampoensis (Schwarz) Deby and Pleurosira laevis (Ehrenberg) Compère from Sinchun Stream in Daegu City (South Korea). We examined their morphology and ultrastructures by LM and SEM, and measured their population growth (number of cells at 24 ~32 days) and growth rate during the exponential phase at different temperatures and with different nutrient concentrations in unialgal cultures. H. whampoensis had maximal population growth and growth rate at 18°C, but P. laevis had maxima at 24°C. The maximum population growth and growth rate of both species was at 32 µM nitrate (NO₃^-). H. whampoensis and P. laevis had maximum growth rates at 25 µM phosphate (PO₄^-3), whereas H. whampoensis had maximum population growth at 10 µM PO₄^-3 and P. laevis had maximum population growth at 25 µM PO₄ ^-3.