Short-term variations of the vertical distribution of cyanobacteria in the open Mediterranean

• Autores: Michel Denis, Valerie Martin, Valerie Andersen
• Localización: Scientia Marina, ISSN 0214-8358, Vol. 64, Nº. 2, 2000, págs. 157-163
• Idioma: inglés
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• Resumen

  • A general study of biogeochemical processes (DYNAPROC cruise, May 1995) was conducted at a station in the open northwestern Mediterranean Sea where horizontal advection was weak. During this experiment, short-term variations of the vertical distribution of cyanobacteria were investigated and a possible link with diel vertical migration was considered. Consistently, the experimental work was conducted at a time scale of a few hours. Cyanobacteria were the most abundant population in the pico- and nanoplankton size-class. Their vertical distribution was monitored over 36 h with a frequency of 4 h. With such a time resolution, they experienced a single grazing event during daytime and, at night, they were heavily grazed when the upper layers were occupied by organisms migrating from the aphotic zone. The corresponding integrated (0-90 m) losses of cyanobacteria during the night amounted to 534 mg C m-2. Though daytime grazing is most likely due to nanoflagellates and microzooplankton, night-time grazing could significantly involve migrant macrozooplankton organisms and sustain a periodic export of organic matter. This study stresses the importance of the potential export of organic matter as a consequence of the diel vertical migration, export that could not be accounted for by measurements at longer time scale.