Horizontal distribution of photo- and heterotrophic microorganisms on the coastal area of the northern Baltic Sea--a case study

The horizontal distribution of bacteria (BACT), bacterial production(FDC), picoplanktonic cyanobacteria (CYANO), and photosynthetic(PNF) as well as heterotrophic (HNF) nanoflagellates was studiedat the end of June on the SW coast of Finland, the Baltic Sea.Samples were taken at 0 and 10 m depths from three transects500 and 800 m apart. The distance between sampling points was20 m. Cell counts of BACT, CYANO, PNF, HNF and the FDC showed3- to 5-fold deviations in the whole data set. Differences betweenthe duplicate counts within the subsamples were 10–20%.Within the transects, the maximum values were 1.2–3.0times higher than the minimum values. Differences between thetransects were statistically significant for all variables exceptFDC. Deviations in cell numbers between the surface and 10 mwere quite irregular. but often statistically significant. Inmost cases, the organism groups did not correlate significantlywith each other. The horizontal distribution of pelagic microbeswas sufficiently uniform, on a meter scale. for one samplingpoint to give a reliable estimate of microbial densities inthe area under investigation. The differences between the surfaceand the lower stratum of the mixed layer (10 m) were in mostcases statistically significant.