The effect of temperature on brood development was investigated for three intertidal hymenosomatid crabs: Halicarcinus cookii, H. varius and H. innominatus in Kaikoura, New Zealand. The duration of brood incubation decreased as temperature increased, as did the interbrood period. The duration of each stage of brood development also decreased with increased temperature, but the proportion of total incubation time for each stage remained relatively similar at different temperatures. Hymenosomatid crabs have determinate growth, but moult to maturity at different sizes, thereafter devoting most of their energy to reproduction. The number of broods a female could carry in her lifetime was estimated for each species. Halicarcinus cookii was estimated to be able to produce eight complete broods of 1146 eggs per lifetime, H. varius was estimated to be able to produce seven complete broods of 1051 eggs per lifetime and H. innominatus was estimated to be able to produce six complete broods of 1081 eggs per life time. With the predicted global temperature rise of 2°C in the next 50 years, the authors estimate that, for all three species, a female could produce one extra brood per lifetime (a 10–15% increase in fecundity depending on species), even more if crabs reach maturity faster, potentially leading to a significant population increase.