北海道南西部恵山沖におけるPseudocalanus minutus と P. newmani (Copepoda; Calanoida) の鉛直分布および生活史

• Main Authors: 山口, 篤, 志賀, 直信
• Format: Article in Journal/Newspaper
• Language: Japanese
• Published: 日本プランクトン学会
• Subjects: Pseudocalanus; vertical distribution; life cycle; southwestern Hokkaido; 660; Pseudocalanus minutus
• Online Access: http://hdl.handle.net/2115/57092

The vertical distributions and life cycles of Pseudocalanus minutus and P. newmani off Cape Esan，southwestern Hokkaido，were investigated. The vertical distribution patterns were examined by using samples collected by Motoda horizontal closing nets (0.35 mm mesh) in July，October and December 1994 and April 1995. For the analysis of life cycle，a series of vertical hauls with a 0.45 m net (0.10 mm mesh) was made at a time interval of 1-2 months from July 1981 to September 1982 and June 1994 to July 1995. The vertical distribution patterns of P. minutus and P. newmani were different in several aspects. P. minutus exhibited a marked seasonal vertical migration，residing near surface in spring and summer，and most copepodite V stage below 200 m in autumn and winter. The copepodite V below 200m was characterized by large deposited oil droplets，and presumed to be in “diapause". In contrast， P. newmani were distributed in the upper 200 m throughout the year. P. newmani were more resistant to higher temperature than P. minutus，th e highest tolerable temperature for the former being estimated to be ca. 15℃. Both P. minutus and P. newmani showed similar seasonal changes in numerical abundance，th e annual peak was reached in 2-3 months after the spring phytoplankton bloom. Life cycle modes of both species were however dissimilar. The analysis of the stage composition of copepodites suggests that the spawning of P. minutus occured mainly in spring，whereas that of P. newmani was throughout the year. The magnitude of reproduction of P. newmani was small through autumn to winter. The present results are compared with those of the both species in other geographical regions.