A high-frequency time series at Ocean Weather Ship Station M (Norwegian Sea): population dynamics of Calanus finmarchicus

Abstract

Between the end of March and mid-June 1997, net samples in the upper 100 m were taken almost daily on Weathership M (Norwegian Sea) to determine the abundance and stage composition of Calanus finmarchicus. Biomass showed high day-to-day variability with several peaks, ranging from 0.05 to 6.3 g C m -2 , with an average of 0.84 g C m -2 . Consequently, stage abundances were also highly variable, but stage composition was consistent. Although population egg production was almost constant throughout the study period, a clear cohort was formed. During the pre-bloom period, nauplii and Copepodite Stage I (CI) were frequently abundant, but further stage development proceeded only during the short bloom. At the end of the bloom, no young nauplii continued to grow, but older stages did. Some specimens had reached CV at the end of the investigation period. The extended seasonal presence of some stages made estimates of stage duration and production difficult. Three different numerical methods were applied to estimate productivity and production. All methods resulted in similar estimates of productivity, 0.031 to 0.055 d -1 , corresponding to a production of 30 to 56 mg C m -2 d -1 . These rates are considerably lower than optimum rates measured in the laboratory, suggesting strong food limitation of growth during most of the observation period.