Choanoflagellida on the southeastern Bering Sea shelf

Seven species of planktonic choanoflagellates, among which Calliacantha nat ans was the most abundant, were found on the southeastern Bering Sea shelf. The C. natans abundance on the outer shelf and in the adjacent deepwater d omain located south of Saint George Island was as high as 3.5 million cells /l. The intensive development of the species was related to the Phaeocystis pouchetii bloom termination. The degradation of the P. pouchetii mucous ma trix resulted in the formation of microcosms with high concentrations of di ssolved and suspended organic matter favorable for the development of bacte rioplankton and heterotrophic nanoplankton. This situation gave rise to the formation of a developed bacterial food web in the planktonic community. T he mode of feeding of C. natans allowed the species to occupy the trophic n iche, which, in the planktonic communities, is usually occupied by ciliates and heterotrophic flagellates.