Longitudinal patterns of spring-intermonsoon phytoplankton biomass,species compositions and size structure in the Bay of Bengal

摘要

Vertical distributions of phytoplankton biomass,compositions and size structure were investigated during the spring-intermonsoon (April 22 to 30) of 2010 along transact 10 N of the Bay of Bengal,northern Indian Ocean.Surface phytoplankton biomass (Chl a) was (0.065 ± 0.009) μg/L,being greater than 80% of which was contributed by pico-phytoplankton (20 μm) accounting for 58% and nano-(3-20 μm) or pico-cells for 15% and 27%,respectively.In particular,the cells concentration coupling well with phosphate level was observed at middle layer (75-100 m) of 87 to 89 E,dominated by micro-cells diatoms (e.g.,Chaetoceros atlanticus v.neapolitana,Chaetoceros femur and Pseudonitzschia sp.) and cyanobacteria (i.e.,Trichodesmium hildebrandtii),with the cells concentration reached as high as 4.0 × 10 4 and 4.3 × 10 4 cells/L.At the rest of the transact however,dinoflagellates (e.g.,Amphisdinium carterae and Prorocentrum sp.) were the dominant species,with the cells concentration varying from 0.3 × 10 3 to 6.8 × 10 3 cells/L.Our results also indicate that the regulation of large cells (micro-,nano-) on phytoplankton biomass merely occurred at DCM layer of the Bay.