SEASONAL VARIATIONS IN THE MORPHOLOGY OF THE COCCOLITHOPHORE CALCIDISCUS LEPTOPORUS AT BERMUDA (N. ATLANTIC)
Sabrina Renaud, Christine Klaas
Geologisches Institut, ETH-Zentrum, 8092 Zürich, Switzerland
The seasonal dynamics of the coccolithophore Calcidiscus leptoporus is considered along a monthly sampled time-series from January 1991 to January 1994 off Bermuda (North Atlantic). At this location, environmental parameters show a high seasonality, from a nutrient-rich winter period associated with water-column mixing, to oligotrophic stratified waters in summer.
Phytoplankton in general and coccolithophore community in particular experience important variations following this seasonal pattern, with high phytoplankton stocks in winter and reduced abundances in summer, although associated for coccolithophores to a higher diversity and evenness of the community, species such as E. huxleyi no longer over-dominating the community.
Calcidiscus leptoporus, a relatively rare species never representing an important proportion of the community, displays variations along this time-series both in absolute abundance and in morphology. Higher abundances as well as a sharp decrease in size, associated with evidence of sexual reproduction, occur in spring when the coccolithophore community reaches a higher diversity after the E. huxleyi dominated winter period. The seasonal dynamics of C. leptoporus therefore appears not to be primarily under control of abiotic environmental parameters, but rather to be the consequence of ecological influences on a complex life-cyle.
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