THE ROLE OF COPEPODS IN THE PLANKTONIC ECOSYSTEMS OF MIXED AND STRATIFIED WATERS OF THE EUROPEAN SHELF SEAS

The European shelf seas can be divided into regions which have tidally mixed waters and thermally stratified waters. The tidally mixed near shore environments support zooplankton communities dominated by smalle r copepods and having large meroplankton contributions. These small co pepods (Centropages spp., Temora spp., Acartia spp., Paral Pseudo/Micr ocalanus spp.) together with the microzooplankton component form a dif ferent and more complex food web than the larger copepod/diatom link a ssociated with thermally stratified waters. The copepods Calanus finma rchicus and C. helgolandicus account for over 90% of the copepod dry w eight biomass in stratified waters. Although occurring in lower number s in mixed waters they can still make significant contributions to the biomass. A 31 year time series from the European shelf shows the inte r- and intra-annual variability of these species. The basic biology an d food web that these two systems support, and the transfer of energy, can result in marked differences in quantity and quality of particula tes available as food for fish larvae. Calanus dominated systems allow the primary production to be directed straight through the trophic fo od chain (diatoms/Calanus/fish larvae) while the near shore communitie s of smaller copepods limit the amount of energy being transferred to the higher trophic levels. Eighty-two Longhurst Hardy Plankton Recorde r hauls were used as the data base for this study. In all cases the zo oplankton was dominated by copepods both in numbers and biomass accoun ting for > 80% of total zooplankton dry weight in the Irish Sea, Celti c Sea, shelf edge of the Celtic Sea and the northern and southern Nort h Sea in Spring.