JPR Advance Access originally published online on March 30, 2004
Journal of Plankton Research 2004 26(6):637-645; doi:10.1093/plankt/fbh065
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Journal of Plankton Research Vol. 26 No. 6 © Oxford University Press 2004; all rights reserved
Relationship between vegetative cells and cyst production during Alexandrium minutum bloom in Arenys de Mar harbour (NW Mediterranean)
Institut de Ciències Del Mar (CSIC), Barcelona, Spain and 1 Instituto Oceanografico Vigo, Vigo, Spain
*Corresponding Author: esther{at}icm.csic.es
A recurrent Alexandrium minutum bloom in the Arenys de Mar harbour (Catalan coast, North Western Mediterranean) was monitored in order to establish the relationship between vegetative cells and cyst production. The bloom lasted from January 21 to February 24, 2002 and reached cell concentrations of up to 47 x 106 cell L1. Two aspects related to the resting cysts deposition were studied: (i) production of resting cysts during the bloom period (by means of sediment traps) and (ii) distribution of resting cysts in the sediment after the bloom (May 2002). Cyst formation in Arenys clearly started in a period with high vegetative cell densities in the water column. Once production was initiated encystment fluxes remained constant for two weeks, and covering the periods of maintenance and decline of the bloom. High cyst fluxes (up to 6000 cysts cm2 day1) were quantified as a result of the high vegetative cell concentration. Moreover, encystment occurring in less than 1% of the total population indicates that most of the cells are not involved in resting cysts formation. A comparison of the resting cyst flux values obtained from the sediment traps and the resting cyst concentrations in surface sediment (6283270 cysts cm3) three months later, revealed that the number of cysts in the sediment decreased during that time. The studies of excystment showed a high germination percentage (91%) and germling viability (100%). These data, together with the resting cyst distribution in the sediment, are important in assessing the role of resting cysts in the bloom dynamics of A. minutum in confined waters.