Factors controlling the temporal dynamics of egg production in the copepod Temora longicornis

The factors controlling the temporal dynamics of egg production rate (EPR) in Temora longicornis were investigated during a 3 yr study. T longicornis produced eggs all year round, with an annual maximum (EPRmax) between 27 and 48 eggs female(-1) d(-1) during spring/summer and minimum of 1.4 eggs female(-1) d(-1) in autumn/winter. The highest EPR values were measured when copepods were heaviest and in situ chlorophyll a (chl) increased above similar to 1 to 3.5 mu g l(-1), irrespective of ambient temperature, EPR was positively related to copepod body weight (BW) and chl, whereas it was negatively related to suspended particulate matter (SPM) and temperature. Stepwise multivariate analysis showed that copepod BW, chl and SPM explained most of the variability associated with fecundity, outweighing the effect of temperature. Moreover, the lower EPRmax measured in spring 1996, as compared to 1997 and 1998, suggests that food nutritional quality was probably another important factor affecting copepod fecundity. Since BW was inversely related to temperature, by controlling copepod BW, temperature indirectly determined the maximum potential reproductive output of T longicornis. Acting on at least in Situ physical parameters like temperature and SPM, climate change could represent an important modulator of secondary production in this and other copepod species.