Abundance and size composition of the summer phytoplankton communities in the western North

• Main Author: Tsuneo Odate
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1996
• Subjects: Bering Sea; Gulf of Alaska; Pacific; Alaska; Aleutian Islands; Copepods
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.525.5420; http://www.terrapub.co.jp/journals/JO/pdf/5203/52030335.pdf

Chlorophyll a concentrations (Chl a) of size-fractionated phytoplankton samples were measured in the western North Pacific Ocean, the Bering Sea, and the Gulf of Alaska during the summer of 1986. Among samples collected in the upper 100 m (total of 210 samples), 207 samples were dominated by micro- (>10 µm) or picoplankton (<2 µm) and only three samples were represented by nanoplankton (2–10 µm). These 207 samples were classified based on the total Chl a content into three types: Type H (>1.0 µg l–1), Type M (0.5–1.0 µg l–1), and Type L (<0.5 µg l–1). These types further divided into two subtypes (-p and-m), depending upon dominancy of pico (-p) and microplankton (-m). The phytoplankton community was represented by Type L-p in the Gulf of Alaska, where 80 % of the samples fell into this type. It was represented by Type M-p in the western North Pacific and the Oceanic Domain in the Bering Sea, where 53 and 41 % of samples were identified as this type, respectively. In the Middle Domain of the Bering Sea, 68 % of samples collected below the nitracline was Type H-m, which indicates blooms of micro-plankton. This type was also observed in the neritic waters near the Aleutian Islands. These types described above are consistent with a general trend that an increase in phytoplankton abundance is attributed to the growth of microplank-ton. An unusual type occurred above the nitracline of the Middle Domain, where microplankton prevailed, although the total Chl a was less (Type L-m). This type represents a feature of late phase of an ice edge bloom. Another unusual type was found mainly in the Outer Domain of the Bering Sea, where the total Chl a was high and picoplankton prevailed (Type H-p). The predominance of picoplankton seems to result from the heavy grazing intensity of large calanoid copepods upon microplankton but not upon picoplankton 1.