The zooplankton biomass in the Sea of Japan

We examined seasonal, annual variation and horizontal distribution of zoopl ankton in the Sea of Japan from 1966 to 1990. Zooplankton was most abundant in the spring. The spring maximum appeared in February-March and in April- May in the southern and eastern parts of the study areas, respectively. In the summer and autumn, a secondary peak was most conspicuous in the eastern part. The difference between the estimated biomass at night and day was la rge in the spring and small in summer and autumn. The biomass in the offsho re southern area peaked about every 3 years between 1966 and 1983, and incr eased abruptly in 1990. The density in the area north of 39 degrees N or 40 degrees N was high. Total biomass estimated in the upper 150 m layer in th e Sea of Japan (10(6) km(2)) was 9.5 x 10(6) t in the daytime and 16.6 x 10 (6) t at night.