Trends in Early Larval Traits of a Global Invader at Home Across a Latitudinal Gradient: The European Shore Crab <i>Carcinus maenas</i>

ABSTRACT Aim This study sets out to understand the variability in larval traits of dispersive life stages of a famous invader, the European shore crab Carcinus maenas , in its native distribution range. Location North East Atlantic coast from the Norwegian Arctic to the southern European distribution limit of C. maenas in Southern Spain. Taxon European shore crab Carcinus maenas (Crustacea, Decapoda). Methods We quantified latitudinal patterns in larval body mass, elemental composition (C and N content), and thermal tolerance of the first larval stage. We collected crabs from four populations spanning 25° of latitude (Vigo in Northern Spain; Bergen, Trondheim, and Bodø in Norway) and reanalysed published and unpublished data of body mass and elemental composition of additional populations from Germany, Wales, France, and Southern Spain. Furthermore, we used two laboratory experiments to test the thermal tolerance limits of the first larval stage from Vigo and the Norwegian populations. In the first experiment, we reared larvae from hatching to Zoea II at seven temperatures (9°C–27°C) and from hatching to LT 50 at 6°C. In the second experiment, we exposed freshly hatched larvae acutely to increasing or decreasing temperatures (up to 40°C and down to 3°C). Results Across the entire European range, we found a substantial increase in dry mass and carbon and nitrogen content of freshly hatched larvae with latitude. Norwegian populations exhibited higher survival at 9°C than the Vigo population. Furthermore, LT 50 at 6°C increased from South to North. All populations showed high survival in the range 12°C–24°C but low survival at 27°C. Main Conclusions Larval tolerance quantified by using survival to Zoea II is not clearly related to the tolerance quantified with the acute experiments, indicating that each method assesses different aspects of thermal tolerance. Tolerance to low temperature correlated positively to tolerance to high temperature, suggesting that variation among females in larval responses reflects a general physiological quality rather than trade‐offs. We provide evidence for potentially adaptive variations in larval body mass and thermal tolerance across a latitudinal gradient for C. maenas .