G.Valet, M.Sieracki1)
Seawater microplankton represents an essential worldwide water ecosystem. It maintains the metabolic balance e.g. by assimilating CO2 from the atmosphere and is part of the food chain for larger animals in the oceans. The study of microplankton organisms is of increasing importance to obtain knowledge on the influence of increased atmospheric CO2 levels as well as of higher UV irradiation levels caused by the rarefication of the ozon layer.
Microplankton is composed of a mixture of many different types of microscopic organisms. Flow cytometric measurements of forward (FCS) and sideward (SSC) light scatter of these cells in combination with natural fluorescence (chlorophyll, phycobiliproteins) result in a complex pattern of overlapping cell populations.
Characteristic differences of microplankton populations around Georges Bank (Cape Cod) are detected by standardized and automated list mode data classification with the CLASSIF1 (2) multiparameter classification program (Ann.NY Acad.Sci.677,233-251(1993), Partec,Münster, Germany). This permits the distinction of individual sample collection positions along a cruise as well as the discrimination of typical microplankton patterns at the sweet/salt water transition area inside Georges Bank, on the bank itself and on its ocean directed side.
No prior knowledge on the microplankton cell populations is required for this analysis i.e. it is applicable for the characterization as well as for the standardized detection of changes in unknown microplankton populations like for the investigation of influences of increased UV-irradiation or CO2 levels as well as altered water quality.