The euryhaline, eurytherm copepod Acartia tonsa plays a key role in many marine food webs as a grazer on phytoplankton and as prey species for commercially important planktivorous fishes. The different populations of this cosmopolitan species experience a wide range of environmental conditions. This study aims to elucidate the response of A. tonsa to changes in multiple environmental factors. The effects of temperature (T), salinity (S) and the interaction of both variables on recruitment processes were investigated to show potential influences of changes in environmental conditions on its life cycle and population dynamics. Estuarine conditions appeared to be optimal for reproduction, despite the marine origin of the population. Interactive effects of T × S were more pronounced when the population was exposed for a longer period of time to constant laboratory conditions. Potential resting eggs were identified based on morphology and hatching characteristics, and were mainly produced at high S and low T. Our results emphasize the importance of investigating the combined effects of different physical factors to gain a better understanding of potential changes in population dynamics resulting from climate-induced changes in key environmental factors.