A MODELING INVESTIGATION OF COPEPOD EGG-PRODUCTION IN THE IRISH-SEA

A combined physical and biological model is used to estimate egg production for two representative species of copepods in the Irish Sea. The model is driven by meteorological and hydrographic data, and calculates stratification and phytoplankton growth. Copepod egg production is calculated from the surface chlorophyll concentration and temperature. Egg production rates of adult female Calanus helgolandicus and Acartia clausii were measured on two cruises in the Irish Sea during May of 1992 and 1993 in conjunction with measurements of chlorophyll and temperature, and the model is compared with these observations. Predictions of chlorophyll and temperature structure for 1992 show goad agreement with the data, and the model successfully simulated the spatial variation of egg production over the region covered by the cruise. In 1993, weather conditions led to earlier stratification and phytoplankton growth, as predicted by the model. The cruise covered a wider area than in 1992 and a wider range of hydrographic regimes and chlorophyll concentrations was observed. The relationship between egg production and chlorophyll agreed well with the data; however, there were discrepancies in the spatial details of the chlorophyll predictions, leading to errors in the modelled egg production. These may have arisen from errors in simulating the timing of onset of nutrient depletion, which was not a significant factor in 1992. The parameter values for the egg production model indicate that the copepods, particularly Calanus, derived energy from foods other than phytoplankton. (C) International Council for the Exploration of the Sea.