The “brown shrimp”, Crangon crangon (Linnaeus 1758), is a benthic key species in the North Sea ecosystem, supporting an intense commercial fishery. Its reproductive pattern is characterized by a continuous spawning season from mid-winter to early autumn. During this extended period, C. crangon shows temporal variations in offspring size and biomass (Urzúa et al. 2012). Shrimps were periodically (January-September, 2009) sampled from a population living in the lower Elbe estuary, North Sea (54º03’-54º04’N; 8º18’-8º24’E; ca 13 m depth). In the laboratory, we quantified seasonal changes in dry weight (W) and carbon content (C) of early-stage eggs and newly hatched larvae. Relationships between biomass data and conditions of temperature and food concentration prevailing during the early life-history stages (oogenesis, embryogenesis, larval hatching) were analysed and modelled.Our data revealed significant seasonal variations, with maximum values of W and C at the beginning of the reproductive season (January), decreasing values throughout spring (April-May), minima in summer (June-August), and a slight increase thereafter. While the absolute values of biomass per offspring showed highly significant differences (P < 0.001), the relative composition (% W) remained similar throughout the reproductive period. According to generalized additive models (GAM), environmental factors affecting the early phases of the reproductive cycle exert significant effects on offspring condition: the C content per egg showed a highly significant negative relationship with day length (r² = 0.40; P < 0.0001), a weak positive relationship with temperature (r² = 0.09; P < 0.05), and a weak negative relationship with food availability (phytoplankton biomass; r² = 0.12; P < 0.05) at the time of beginning oogenesis. The C content per larva was positively correlated with the embryonic carbon content shortly after egg laying (r² = 0.60; P < 0.001) and negatively with the average incubation temperature during the period of embryogenesis (r² = 0.35; P < 0.001). Water temperature (r² = 0.57; P < 0.001) and phytoplankton biomass (r² = 0.39; P < 0.001) at the time of hatching were negatively correlated with larval C content at hatching. “Winter larvae” hatching from larger “winter eggs” showed higher initial values of biomass compared to “summer larvae” originating from smaller “summer eggs”. This indicates carry-over effects persisting from the embryonic to the larval phase. Intraspecific variability in larval biomass is interpreted as part of an adaptive reproductive strategy compensating for strong seasonality in plankton production and transitory periods of larval food limitation.