Microbial Eukaryotes in Marine Oxygen Minimum Zones

Abstract

Increasing ocean temperatures and anthropogenic influences are contributing to marine oxygen minimum zone (OMZ) expansion, with consequent changes in nutrient and climate-active trace gas cycling. As a result, bacterial and archaeal mediation of biogeochemical transformations within marine OMZs has received attention. Less is known about the role of protists within OMZs, despite their potential importance to biogeochemical cycles. Here, we discuss responses of protist populations to water column oxygen deficiency in three ecosystems: the Saanich Inlet, a seasonally anoxic fjord on the coast of Vancouver Island, British Columbia, and two examples of permanently anoxic/sulfidic end-member water columns in Cariaco Basin (Venezuela) and Framvaren Fjord (Norway). Small subunit ribosomal RNA gene sequencing approaches partnered with multivariate statistical methods have been used to characterize microbial eukaryotes in each of these habitats. Common and unique patterns of community composition exist between the three locations reflecting different responses of components of the protistan community to specific geochemical parameters. Within Saanich Inlet, temporal fluctuations in rare populations of ciliates and flagellates may be significant to biogeochemical cycling particularly as a result of symbioses with, and predation on, other microbes.