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

Abstract

The horizontal distribution of bacteria (BACT), bacterial production (FDC), picoplanktonic cyanobacteria (CYANO), and photosynthetic (PNF) as well as heterotrophic (HNF) nanoflagellates was studied at the end of June on the SW coast of Finland, the Baltic Sea. Samples were taken at 0 and 10 m depths from three transects ∼500 and 800 m apart. The distance between sampling points was ∽20 m. Cell counts of BACT, CYANO, PNF, HNF and the FDC showed 3- to 5-fold deviations in the whole data set. Differences between the duplicate counts within the subsamples were 10–20%. Within the transects, the maximum values were 1.2–3.0 times higher than the minimum values. Differences between the transects were statistically significant for all variables except FDC. Deviations in cell numbers between the surface and 10 m were quite irregular. but often statistically significant. In most cases, the organism groups did not correlate significantly with each other. The horizontal distribution of pelagic microbes was sufficiently uniform, on a meter scale. for one sampling point to give a reliable estimate of microbial densities in the area under investigation. The differences between the surface and the lower stratum of the mixed layer (10 m) were in most cases statistically significant.