This study compares the effect of temperature on the post-embryonic development time and weight-specific growth rate in 2 populations of Acartia clausi from different biogeographic areas (northern and southern Europe). Development was followed from nauplius 1 to adult at 3 temperatures (10, 15 and 18 degrees C) at saturating food conditions. The relationship between development time and temperature was established by fitting Belehradek's function. The northern population had a shorter generation time at all temperatures. At 10 degrees C, the development time was estimated to be 33.9 and 36.4 d decreasing to 16.3 and 17.4 d at 18 degrees C for the northern and southern populations, respectively. Prosome length decreased with temperature, and the southern population had longer individuals at all temperatures. ANCOVA revealed a significant (p < 0.001) positive effect of temperature on the growth rates, and nauplii grew faster than copepodites (except at 18 degrees C in the southern population and 20 degrees C in the northern population). Significant differences between populations were noted during larval growth, with nauplii from the north growing faster at high temperatures (18 degrees C). The results indicate that the 2 A. clausi allopatric populations subjected to different temperature regimes have different temperature responses, in particular at high temperatures.