Environmental control of mesozooplankton community structure in the Seine estuary (English Channel)

This paper is the first to describe the spatio-temporal changes of mesozooplankton in the Seine estuary. Monthly samples were collected along the estuary in 1996 in order to analyse the seasonal changes of the mesozooplankton community and to identify the major environmental parameters that may influence the spatial distribution of zooplankton in this megatidal estuary. Statistical analysis (canonical correspondence analysis) showed that salinity was the main factor correlated with the longitudinal distribution of zooplankton. Marine species (Temora longicornis, barnacle larvae…) were located in the outer part of the estuary, while more oligohaline species (Eurytemora affinis) were recorded in the inner part of the estuary. A mixed zone was characterised by the presence of the neritic copepods Acartia spp. and Eurytemora affinis. The marine species (e.g. T. longicornis, Oikopleura dioica, Barnacle larvae) showed maximum abundance at the end of spring (June) while the most abundant estuarine species, E. affinis, peaked in late winter-spring and declined with the onset of summer. This copepod dominated the estuarine zooplankton throughout the year, and found in the Seine estuary very high favourable conditions to exhibit ultimate abundances (> 190 000 ind m^–3) which is one order of magnitude higher than those found in other European estuaries. It represented the main prey for major planktonivorous species such as suprabenthic and fish species located living in the upstream zone of the Seine estuary.