Thermal tolerance of single larval stages has rarely been studied, eventhough the larva might be the actual physiological bottleneck of all life history stages setting distribution limits. Therefore, temperature tolerance of Zoea I was examined in two different population of the Chilean kelp crab Taliepus dentatus. We measured activity, oxygen consumption, cardiac performance and the CN composition of larval T. dentatus of two populations from central and southern Chile at various temperatures (1) to determine at which organisational level T. dentatus larvae get first affected by temperature, integrating variables from the organismal, tissue functional to the biochemical elemental level, and (2) to compare the thermal tolerance of larvae from varying environmental temperature regimes to look at functional differences between populations as a correlate of adaptation capacities of the Zoea. Our mechanistic analysis explicitly sheds light on how temperature affects the physiology of crab larvae. We found that the highest organisational level gets affected first, seen in activity decrements at unsuitably high or low temperatures, paralleled by decreases in oxygen consumption rates. Cardiac performance is more robust to temperature changes. Heart beat rate decreases only at very high and low temperature extremes and stroke volume is almost temperature independent. The comparison between the southern and central populations showed a limited but clear adaptation of larvae from the southern sampling site to the colder environmental temperature regime, visible at all organisational levels.