ICES Phytoplankton and Microbial Plankton Status Report 2009/2010

In the North Atlantic and connected seas, as elsewhere in the world’s oceans, microbes are extremely numerous, with abundance exceeding, by orders of magnitude, those of any other planktonic group (>107 microbes ml–1). Not only do microbes constitute the largest reservoir of biomass involved in energy and material transfer, but also the largest reservoir of genetic information involved in supplying functional players to the ecological theatre. Microbial plankton are ribosome-encoding organisms from all three domains of cellular life (Bacteria, Archaea, Eukarya) as well as capsidencoding organisms (viruses). Cellular microbes obtain energy from light (phototrophy) or chemicals (chemotrophy), electrons from water (lithotrophy) or organic carbon (organotrophy), and carbon from inorganic (autotrophy) or organic (heterotrophy) compounds, with the possibility of mixed modes of nutrition (mixotrophy). In oxygenated waters of the euphotic zone, primary production (virtually entirely microbial) is carried out by phytoplankton, which are photolithoautotrophs, comprising a huge diversity of algae of domain Eukarya and cyanobacteria of domain Bacteria. Microbial secondary production is carried out by chemoorganoheterotrophs belonging to the domain Bacteria.