Vertical distribution and population structure of Calanus finmarchicus at station India (59 degrees N, 19 degrees W) during the passage of the great salinity anomaly, 1971-1975

Abundance, vertical distribution and stage composition of Calanus finmarchi cus was analysed for a period of four and half years, 1971-1975, based on d ata collected at weather station India in the North Atlantic (59 degrees N, 19 degrees W). The passage of the Great Salinity Anomaly in the area was r eflected by a decrease in the salinity from 1973 to 1975. Calanus finmarchi cus arrives at the surface by the end of March and stays in the upper 50 m, but with a stage segregation in the vertical distribution, until the desce nt periods at the end of May-June and in August-September. During this peri od two or three cohorts develop, apparently in close relation with the phyt oplankton pulses. Abundance is highly variable, with maximum values ranging from 8770 ind m(-2) in 1974 to 56,541 ind m(-2) in 1973. There was no clea r effect of the Great Salinity Anomaly, the maximum abundance occurring the year the Great Salinity Anomaly arrived, 1973, and the minimum values occu rring the next year, 1974, when the effect of the Great Salinity Anomaly wa s well established. However, the structure of the population seems to have been affected during the Great Salinity Anomaly. Possible interactions betw een phytoplankton blooms, the Great Salinity Anomaly and C. finmarchicus po pulation dynamics are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.