Project: Basin-scale distribution and activity of deep-sea protists in the North Atlantic Ocean

ABSTRACT

Little is known about the distribution and ecology of eukaryotic microbes of the deep sea water column. Most of these microbes are small heterotrophic flagellates that feed on bacteria, where biomass in turn is fueled by the input of dissolved and particulate organic material from the surface. This study seeks to understand the distribution of eukaryotic microbes (i.e., protists) in the context of large, basin scale variations in hydrographic and chemical properties. The main hypothesis is that the abundance and taxonomic composition of protists serve as sensitive indicators of the strength and type (particulate or dissolved) of input of organic carbon into the deep ocean system. Samples in vertical profiles targeting major water masses across the North Atlantic will be collected. In addition, deep sea samples will be retrieved under pressure and incubated at in situ pressure and temperature in four newly designed chemostat systems. These cultures will be sub-sampled under pressure and examined for nutrient concentration, as well as for the purpose of monitoring the abundance of both prokaryotes and protists in the chambers. Using the same pressure samplers in short-term incubations, the investigators will explore the activity of deep sea protists by investigating the proportion of actively feeding organisms on fluorescently labeled bacteria. They will enumerate deep sea protists using a combination of fluorescence in situ hybridization and traditional staining methods, and will support taxonomic classifications using electron microscopy. Semi-automated epifluorescence microscopy with image analysis capabilities will be used to scan major filter areas and probe for rare microbes that normally fall below detection limits of other methods. In laboratory experiments, the investigators will use the newly built culture system to study pressure effects of eukaryotic protists while simulating temperature and pressure changes that sinking particles are exposed to when they sink to the abyss.