Aspartate transcarbamylase du mesozooplancton et prerecrutement de la sole: les conditions d’une approche systémique en Manche

In temperate neritic areas, meteorological conditions prevailing during winter and the following spring play a major role on the main features of the spring development pattern of pelagic ecosystems. Interannual fluctuations of this environment lead to qualitative and quantitative variations of secondary production which may strongly influence processes regulating the recruitment of many species. A method for assessing pelagic secondary production is based on measurement of the activity of an enzyme, aspartate transcarbamylase, and has been carried out during spring periods for six years in succession, in the southwestern part of the English Channel. These works have permitted the establishment of a close correlation between the quantitative variations of this enzyme activity and changes in biomass with time of the mesozooplankton community. For the same years, other authors have performed, in the eastern English Channel, the assessment of sole pre-recruitment, which shows striking analogies with interannual variations of the secondary production index. Therefore, from a macroscale point of view, more or less favourable years appear in quite agreement for both estimates. The general oceanographical features, the spatio-temporal scales of involved processes are presented and allow to explain why, and within what limits, such results can be successfully achieved for some fish populations and especially sole in the English Channel.