GROWTH AND GRAZING LOSS RATES IN SINGLE-CELLED PHAEOCYSTIS SP (PRYMNESIOPHYCEAE)

Growth and grazing loss rates of natural Phaeocystis sp. single cells were measured using a seawater dilution technique. Measurements were performed during an intense Phaeocystis sp. bloom in the North Sea between 19 April and 5 May 1988. Experimental results yielded rapid carbon turnover rates. Population growth rates varied from 0.033 to 0.098 h-1, grazing loss rates from 0.037 to 0.174 h-1. From measured growth rates, average doubling rages of 1.3 doublings d-1 were calculated. The growth rates would have resulted in maximum carbon production rates of 146 mg C m-3 d-1. Grazing rates increased in the course of the bloom and exceeded growth rates at the end. Grazing loss was caused primarily by microzooplankton feeding. Ciliates and heterotrophic dinoflagellates were identified as the major potential consumers of single cells of Phaeocystis sp. at the beginning of the bloom. The grazing impact of larger microzooplankton species appeared to increase during the progressing bloom. © 1990 Springer-Verlag.