Interannual variability of metazooplankton biomass in ocean margins: late winter vs. summer

The main goal of this part of the Department of Energyʹs (DOE) Ocean Margin Program (OMP) was to quantify metazooplankton biomass and its composition in relation to hydrographic variables. The study periods were March, and June/July 1994 and 1996. Meteorological forcing was not pronounced during the periods of observation. Hydrographic conditions differed clearly between March 1994 and 1996, which was reflected in zooplankton biomass in the entire water column (mg C m−2), which was higher in 1994 and 1996. There was little difference during summer in hydrographic conditions and metazooplankton biomass between 1994 and 1996. Local biomass maxima were much more pronounced in March than during summer. The magnitudes of biomass abundance in March are close to the highest values encountered elsewhere on continental shelves and slopes. Those in summer only occasionally reflect those of highly productive ocean margins. mposition of dominant taxa hardly varied between the March studies, but differed to some extent between June 1994 and July 1996. The composition of post-naupliar stages of the abundant copepod genera Centropages and Temora differed within seasons, showing different states of reproductive activity. Short-term observations like ours on the abundance, distribution and composition of metazooplankton assemblages provide limited insight into intraseasonal and interannual variability.