Journal of Plankton Research Vol.22 no.12 pp.2181-2203, 2000
© Oxford University Press 2000
Observations of flagellates in colonies of Phaeocystis globosa (Prymnesiophyceae); a hypothesis for their position in the life cycle
National Institute for Coastal and Marine Management / RIKZ, P.O. Box 8039, NL-4330 EA Middelburg, The Netherlands, 1 Forschungs- und Technologie-Zentrum Westküste, Hafentörn, D-25761 Büsum, Germany and 2 University of Groningen, Department of Marine Biology, P.O. Box 14, NL-9750 AA Haren, The Netherlands
Flagellates of Phaeocystis globosa were observed inside colonies in North Sea samples in 1992. Field data suggest that low phosphate concentrations (
0.5 µM) and, as a consequence of sedimentation, a 20- to >100-fold reduction of daily irradiance (to <10 W h m2 day1), triggered the transition of non-flagellate colonial cells to flagellate cells. The colonial flagellates appeared to be similar to cultured solitary Phaeocystis microflagellates; these flagellates do not produce pentagonal stars. Nevertheless, pentagonal stars were observed inside the colonies. This implies that two types of flagellates, microflagellates and the larger pentagonal star-producing mesoflagellates, are formed simultaneously in Phaeocystis colonies. Therefore, this observation fills a missing link in the life cycle of Phaeocystis. It is proposed that micro- and mesoflagellates are the Mikrozoosporen described by Kornmann (Helgoländer Wiss. Meeresunteruchungen 1955, 5, 218233) and that these flagellates are comparable to the small and large zoids described by Parke et al. (J. Mar. Biol. Assoc. UK 1971, 51, 927941). Thus, four different cell types can be distinguished in the life cycle of P.globosa: (i) the haploid microflagellate (3.1 ± 0.1 µm), (ii) the haploid mesoflagellate (4.2 ± 0.1 µm), (iii) the diploid macroflagellate (67 µm) which is Kornmann's (Kornmann, 1955) Makrozoospore, and (iv) the diploid non-flagellate colonial cell (6.1 ± 0.2 µm). A life cycle for Phaeocystis is presented, and the life-cycle transitions still to be tested are identified.
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