In the common prawn, Palaemon serratus (Pennant, 1777), the females release larvae twice a year (winter and summer layings). We investigated seasonal differences in larval phenotypes and their consequences on larval performance. We measured the biomass and carbon (C) and nitrogen (N) content (proxy of lipid and protein reserves) at hatching of larvae laid by 6 winter and 6 summer females collected on the coast of Seine-Maritime (France). We incubated these larvae at 3 temperatures (12, 16, and 20 ◦C) and quantified the effects of tem- perature and season on survival, development time, biomass, and C and N content and ratio at metamorphosis. At hatching, winter larvae were larger than summer larvae, but their C/N was similar. Development time increased with decreasing temperature, with no seasonal difference. Within the same clutch, the longer the development time, the greater the weight of the larvae, without affecting their C/N ratio. Seasonal differences in maternal per offspring investment were not as pronounced as expected. Surprisingly, the summer larvae survived and grew better than the winter ones, at least at 16 and 20 ◦C.