Phytoplankton of the Amur River Estuary (Sea of Okhotsk) during the summer periods of 2005–2007

The qualitative composition of planktonic microalgae in the Amur River Estuary (in the Sea of Okhotsk) was studied in July 2005, June 2006, and June 2007. The biomass and abundance of phytoplankton were studied for the first time. The average cell density of the microalgae ranged from 194700 to 855100 cells/liter, being higher in 2006 than in 2005 and 2007. The average biomass of the community varied from 1.06 g/m³ in 2007 to 3.17 g/m³ in 2006. Analysis of the similarity of the species composition and cell density of the phytoplankton revealed two groups of stations: the first includes stations in the northern and central parts of the Amur Estuary; and the second includes stations in the southern and central parts. The first group was characterized by the predominance of freshwater diatoms and a high abundances of green and blue-green algae and the second group was characterized by the predominance of marine microalgae. The high cell density and biomass of phytoplankton were due to the increased nutrient input via the river runoff of the Amur.