Seasonal variations in biochemical composition of phytoplankton in the East/Japan Sea

Abstract:

Biochemical compositions (carbohydrates (CHO), proteins (PRT), and lipids (LIP)) of phytoplankton in the East/Japan Sea were analyzed to estimate its growth phases, nutritional values, and environmental growth conditions during two different Korea-Russian joint research cruises, October 2012 and April 2015. The integrated chlorophyll-a (chl-a) concentration was much higher in April 2015 (average ± S.D. = 91.6 ± 66.6 mg chl-a m^-2) than in October 2012 (average ± S.D. = 21.5 ± 6.7 mg chl-a m^-2). The small-sized phytoplankton (0.7 – 5 μm) contributed largely (49.1 ± 17.5%) to the total chl-a concentration in October 2012, whereas the middle-sized phytoplankton (5 – 20 μm) was dominant accounting for 42.2 ± 3.9% in April 2015. In general, contribution of lipids was higher than other components in October 2012 (CHO: average ± S.D. = 29.5 ± 4.7%; PRT: 28.1 ± 4.6%; LIP: 42.4 ± 4.7%), which suggest that the phytoplankton may be in nitrogen deficiency condition at that time. In contrast, carbohydrates was dominant in April 2015 (CHO: 53.4 ± 7.1%; PRT: 25.7 ± 5.5%; LIP: 20.9 ± 4.5%). The polysaccharide formation for mass flocculation processes by phytoplankton might be one of potential reasons for high carbohydrate contents during the study period in 2015, because carbohydrates are mostly composed of polysaccharides in phytoplankton.