Short-term variation of phytoplankton assemblages in Mediterranean coastal waters recorded with an automated submerged flow cytometer

Abstract

Short-term variations of phytoplankton communities are poorly documented. To overcome these limitations and make observations on a short-time (hours) scale, we moored a submersible flow cytometer (CytoBuoy b.v.) in the Bay of Marseille. The CytoSub monitored phytoplankton every 30 min at a fixed site (2 m depth) during summer 2005. The data treatment, conducted on the basis of pulse-shape analysis, resolved seven clusters. Daily sampling of nutrients and continuous information on salinity, temperature and wind speed allowed distinction between diel cycles and the impact of environmental factors on phytoplankton communities. Autocorrelation of the time series showed a significant periodicity of ∼24 h for most of the clusters during undisturbed meteorological conditions. Two clusters had regular daily abundance variations in the range 0->10 3 cells cm −3 . Two strong wind events revealed similar cluster succession patterns occurring over several days after the wind events. These results provided by the high frequency in situ analysis suggest that the flow cytometry resolved clusters, showing independent behaviour and distinct environment-correlated variations, which may be considered as functional groups. We point out its potential for global oceanic observing systems for which such systems could provide real biological information.