Measuring zooplankton standing stock and production is a central problem in marine biology since zooplankton, particularly copepods, link primary productivity to fisheries productivity. The aim of the present study was to determine the seasonal and annual variation in the standing stock and secondary production of the main calanoid copepod species found in the Menai Strait, eastern Irish Sea between January 1996 and December 1997. In addition, the reproduction and the respiration rate of the dominant copepod species, Temora longicornis, was investigated between 1996 and 1998 to study its population dynamics. The in situ temperature during January through to April differed between years, with the winter 1996 being colder than that of 1997 and 1998. The timing of the spring phytoplankton bloom also differed between years with the Chla maximum in 1996 occurring ~1 month later than in 1997 and 1998. T. longicornis produced eggs all year round with maximum carbon-specific egg production rates (EPR) of (~0.14 d ^-1) coinciding with the spring phytoplankton bloom and minimum rates (~0.01 d ^-1) in winter. The pattern of natural EPR variability indicates that individual fecundity was positively related to female weight and food quantity and negatively related to tidal range (i.e. total suspended sediment). In all three years, the hatching success (% HS) of the eggs laid decreased up to ~80 % during peak phytoplankton production and was significantly negatively correlated (r = -0.47, p<0.05, d.f.= 96) with ambient Chl-a concentration. These non-hatching eggs could have been diapause eggs. The respiration rate of T. longicornis varied during the year increasing both with body weight and with temperature. The metabolic daily energy loss of an adult copepod account for between 4 % and 8 % of its body carbon (winter and summer respectively). Maximum total copepod standing stock occurred during the spring phytoplankton bloom and minimum between autumn and winter with total annual standing stock in 1996 (618 mg-C m^-3) being ~ 4 times lower than in 1997 (2530 mg-C m^-3). Calanoid copepod total annual production varied between 37-160 mg-C m^-3 yr^-1 for 1996 and 1997 respectively with T. longicornis accounting for ~50 % of the total followed by C. hamatus (~25 %), A. clausi (~20 %) and Pseudocalanus sp. (5 %). Annual carbon flow in the Menai Strait was estimated from copepod production with measures of primary production, production of bacteria and ciliates at this site. It is suggested that since the spring increase in T. longicornis population could not be attributed to the EPR of over-wintering females alone, the excess of copepods may either originate from the hatching of resting eggs during winter or from transport of animals from southern regions. If resting eggs were implicated in copepod population dynamics the annual variation in copepod standing stock may be controlled by climate change through differential hatching rate of resting eggs in winter.