Abstract
Regionalisation aims at delimiting provinces within which physical conditions, chemical properties, andbiological communities are reasonably homogeneous. This article proposes a synthesis of the manyrecent regionalisations of the open-sea regions of the Mediterranean Sea. The nine studies consideredhere defined regions based on different, and sometimes complementary, criteria: dynamics of surfacechlorophyll concentration, ocean currents, three-dimensional hydrological and biogeochemicalproperties, or the distribution of organisms. Although they identified different numbers and patterns ofhomogeneous regions, their compilation in the epipelagic zone identifies nine consensus frontiers,eleven consensus regions with relatively homogeneous conditions, and four heterogeneous regions withhighly dynamical conditions. The consensus frontiers and regions are in agreement with well-knownhydrodynamical features of the Mediterranean Sea, which constrain the distribution of hydrological andecological variables. The heterogeneous regions are rather defined by intense mesoscale activity. Thesynthesis proposed here could constitute a reference step for management actions and spatialplanning, such as the application of the European Marine Strategy Framework Directive, and for futurebiogeochemical and ecological studies in the Mediterranean Sea.