Microzooplankton herbivory and bacterivory in the North Water Polynya

Abstract

Polynyas are regions of reduced ice cover in high latitude environments, which are ordinarily ice-covered. There are few comprehensive studies of microbial processes in polynyas although there are many of phytoplankton and metazoans which show their productivity is greater than surrounding regions. Here I report rates of growth of microbial prey and pattems of microzooplankton herbivory and bacterivory in the North Water Polynya (NOW), from April through July, 1998. Growth rates ranged from 0.0 to 1.1 day⁻¹ for phytoplankton and 0.0 to 1.2 day⁻¹ for bacteria. Highest bacterial grazing mortality was during July (1.3 day⁻¹) whereas for phytoplankton highest mortality was during late April (2.2 day⁻¹). Further investigation of protist size-dependent grazing, using high-resolution image analysis, indicated that microzooplankton were preferentially grazing small-sized bacteria. A substantial amount of carbon was channeled through the microbial food web in the NOW suggesting that microbial processes cycle large amounts of biogenic carbon in this polar region.