The Chrysochromulina polylepis bloom in the Kattegat (Scandinavia) May- June 1988. Distribution, primary production and nutrient dynamics in the late stage of the bloom

Chrysochromulina polylepis Manton & Parke bloomed in the Kattegat and the Skagerrak in May-June 1988 and its distribution, as well as primary production and nitrogen dynamics, were investigated in the Kattegat just prior to the decline of the bloom. The bloom occurred throughout the Kattegat area as a subsurface population associated with the pycnocline. The flagellate was actively photosynthesizmg but light-limited in the pycnocline. The primary production of the Chrysochromulina layer represented 50 to 90 % of the total water column production. The specific growth rate of the flagellate was low with doubling times of 4 to 23 d. Ammonium was the major nitrogen source during this late stage of the bloom, accounting for 50 to 85 % of the daily nitrogen uptake. The hourly uptake of ammonium was equal to or exceeded by the ammonium regeneration rate. A minimum primary production of 800 to 1100 fig C 1-I and a nitrogen demand of 10 to 13 fimol N 1-I were estimated from the oxygen supersaturation. Profiles of salinity, temperature and oxygen indicate that the nitrogen was supplied by an intrusion of nutrient-rich water in the pycnocline layer early in the bloom. Possible models for the bloom developments are discussed.