Effect of warming on European green crab (Carcinus maenas) populations from larvae to sexual maturity

Understanding the effects of climate change on the physiology of marine species, particularly during their early life stages (larvae and juveniles), is essential for predicting population dynamics. Carcinus maenas is a widely distributed species of significant ecological and economic importance. This experimental study investigates the effects of warming on the early life stages of the European green crab, C. maenas, through two complementary experiments: (1) larval development and survival were assessed under three temperature regimes—approximately 18.5 °C (representing the annual average Portuguese seawater temperature between 1980 and 2020, used as the control), and two projected climate change scenarios: RCP 4.5 (+1.5 °C) and RCP 8.5 (+3.5 °C), and (2) juvenile survival and growth were monitored in mesocosms from early settlement to sexual maturity. Results indicated that larval mortality exceeded 90 % across all treatments, with 75 % occurring within the first 8 days (95 % CI: 7–8), and that warming enhanced larval survival, with the RCP 4.5 scenario yielding the highest survival rates compared with the control. Additionally, warming also reduced the pelagic larval duration, which declined from 27 (±2) days at 18.5 °C to 16 (±1) days at 22 °C. Similarly, the duration of the megalopa (settlement) stage decreased from 10 to 6 days. Therefore, despite high mortality, accelerated development under warming may enhance population resilience. Juvenile mortality was also high, with 50 % of settled individuals dying within the first 50 (95 % CI: 31–46) days, and differences in growth and survival between sexes were observed: females reached sexual maturity faster than males 83 ± 12 and 109 ± 20 days, respectively. Moreover, only 24 % (95 % CI: 16–34) of the settled females reached sexual maturity, compared to just 9 % of males (95 % CI: 5–18). These results indicate that C. maenas reach reproductive maturity within six months. The biological data reveal a fast growth increment, high larval and juvenile mortality, and suggest that projected climate change scenarios through the end of the century will have a limited impact on the species' population dynamics and recruitment. • Larval mortality rates exceeded 90 % across all temperature treatments. • Warming accelerated larval development and increased survival. • Juvenile mortality was high, with 50 % dying within the first 50 days. • Juveniles reached sexual maturity in less than four months. • Females reached sexual maturity faster than males.