The bacterial component of the oceanic euphotic zone

Bacteria in the open sea remote from land are sustained strictly on local s ources of organic production which should make understanding their nutritio n and growth regulation easier than in nearshore systems, estuaries and lak es. Until now, a paucity of data from geographically isolated oceanic sites prevented ready :interpretation. In the past decade investigation of bacte rial properties in oceanic systems has increased rapidly, stimulated in par t by large oceanographic programs like the Joint Global Ocean Flux Study. H ere I review comprehensive investigations of bacterial biomass and producti on dynamics in the subarctic north Atlantic and north Pacific, oligotrophic gyres in both oceans, upwelling provinces in the equatorial Pacific and no rthwest Arabian Sea, and in the Ross Sea, Antarctica. Euphotic zone bacteri al stocks are remarkably similar across all except the last regime, averagi ng about 1 g C m(-2). Production and growth rates vary more widely, suggest ing independent regulation of biomass and production. The seasonal to annua l mean ratio of bacterial to primary production is usually below 20%. (C) 1 999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.