Size fraction of chlorophyll a during and after brown tide in Qinhuangdao coastal waters

Picophytoplankton algal blooms occurred in Qinhuangdao coastal water in June 2011.Three cruises were carried out during and after the bloom,and size fraction of chlorophyll a and marine environmental factors were investigated in June to August of 2011 in the area.The average values of Chlorophyll a in non-bloom period and bloom period was 10.85±5.13 μg/L and 5.50±3.60 μg/L,respectively.The surface distribution of size fractioned phytoplankton in the area was discussed.The correlations of the size fractionated chlorophyll a with the environmental factors were also studied.The results showed that the chlorophyll a of microplankton( 20μm),nanoplankton(2-20 μm) and picoplankton(0.74-2 μm) accounted on average for 2.1%,48.3% and 49.6% of the total chlorophyll a in the whole investigated sea area respectively in June.In July,the chlorophyll a of microplankton,nanoplankton and picoplankton accounted on average for 14.4%,51.6% and 24.0%,respectively.Correlation analysis of size fractionated chlorophyll a with environmental factors revealed that the correlation coefficients of nitrate with size fractionated chlorophyll a varied from negative to positive with the increase of the cell size in the investigated sea in June.Nanoplankton and picoplankton were significantly and positively related with DO(p0.01).