The bacterial component of the oceanic euphotic zone

Bacteria in the open sea remote from land are sustained strictly on local sources of organic production which should make understanding their nutrition and growth regulation easier than in nearshore systems, estuaries and lakes. Until now, a paucity of data from geographically isolated oceanic sites prevented ready :interpretation. In the past decade investigation of bacterial properties in oceanic systems has increased rapidly, stimulated in part by large oceanographic programs like the Joint Global Ocean Flux Study. Here I review comprehensive investigations of bacterial biomass and production dynamics in the subarctic north Atlantic and north Pacific, oligotrophic gyres in both oceans, upwelling provinces in the equatorial Pacific and northwest Arabian Sea, and in the Ross Sea, Antarctica. Euphotic zone bacterial stocks are remarkably similar across all except the last regime, averaging about 1 g C m(-2). Production and growth rates vary more widely, suggesting independent regulation of biomass and production. The seasonal to annual mean ratio of bacterial to primary production is usually below 20%. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.