ГЕТЕРОТРОФНЫЙ МИКРОПЛАНКТОН ЮЖНОЙ ОКОНЕЧНОСТИ ЖЕЛОБА СВЯТОЙ АННЫ В ОСЕННИЙ ПЕРИОД (КАРСКОЕ МОРЕ)

Abstract

The paper concerns the pelagic microbial community of the southern part of the St.Anna trough in the late vegetation period. in 2007 and 2011. The abundance, biomass and production of bacterioplankton, as well as the abundance and species composition of heterotrophic flagellates and ciliates were analyzed. The abundance and bacterial production values observed in the trough were significantly lower than the values typical of the surface brackish water layer above the Kara Sea shelf. The bacterioplankton abundance values of the upper warm layer in 2007 were several times lower than in 2011 (10-60*103 cells/ml and 24-147*103 cells/ml, respectively). In the deeper water layers, this difference diminished. The interannual differences in the values of bacterioplankton production were also most pronounced in the upper 60-meter layer: 0-0.17 and 0.05-0.87 mgC/m3 per day in 2007 and 2011, respectively. The distribution of the abundance of heterotrophic flagellates and ciliates is significantly influenced by the contour current along the slope of the trench. In the area of its influence in 2007, high values of the number of flagellates (154 ± 29 cells/ml) were observed throughout the water column, whereas in 2011 maximal values were confined to the upper 50-meter layer, exceeding almost twice the abundance at neighboring stations (810 ± 102 and 481 ± 61 cells/ml, respectively).The results of multifactor analysis showed that the number of heterotrophic flagellates, as well as the number of protozoan species decreased with depth. However in the euphotic layer there was a difference between two years of observations: in 2007, the abundance of consumers depended on the state of primary producers, whereas in 2011 the main factor affecting their abundance was the number of bacteria. Analysis of the species composition of heterotrophic flagellates suggests that the complex vertical hydrophysical structure of the water column does not affect substantially the microbial community of the region. However the influence of main currents of the area under consideration may be traced regarding the distribution of the abundance and species composition of heterotrophic microorganisms.