Phaeocystis pouchetii at the eastern Bering Sea shelf

During the three spring-summer seasons of 1992-1994, the distribution of Phaeocystis pouchetii was studied in the middle and outer domains of the southeastern Bering Sea shelf, in the deepwater areas adjacent to the continental slope, and in the coastal zone of the Pribilof Islands. The P. pouchetii blooms were encountered in the late spring (June 1993) and in the summer(July 1994) seasons at a water temperature of 4-8 degreesC. The duration of blooms varied from two to four weeks and longer. In the course of the blooms, the maximum number of P. pouchetii colonies reached ten thousand per liter, and the peak abundance of solitary cells was as high as a few million per liter. Along with P. pouchetii, other phytoplankton species, mainly from diatoms, were abundant too. Degradation of the Phaeocystis blooms at the shelf was accompanied by an increase in the abundance of bacterioplankton, geterotrophic nano- and microplankton, in particular, and choanoflagellates. A great biomass of the Phaeocystis colonies under degradation in the shallow coastal zones of the islands and in some parts of the middle shelf sinks down to the bottom and is involved in the benthic foodweb. At the outer shelf, in the part of the domain of the middle shelf, and in the deepwater areas adjacent to the continental slope, most of the Phaeocystis biomass is utilized in the pelagic foodweb, to a great extent, through the bacterial trophic chain.