Effects of CO2 and Temperature on Early Life-Stage Development in the American Horseshoe Crab, Limulus polyphemus

It is important to anticipate the effects of global climate change on the fitness and viability of living marine resources (LMRs). The horseshoe crab, Limulus polyphemus, is an important LMR as a food source for migratory birds, a medical model, and bait for various fisheries. Females typically excavate a nest in beach sand of intertidal habitats and lay distinct clutches of eggs. After hatching, the horseshoe crab larvae disperse from their nest into the sea during tidal inundation. This study aimed to investigate future climate effects, particularly sea-water temperature and acidity, in early life-stages of horseshoe crab development under single stressor (temperature) and multi-stressor (temperature and CO₂) scenarios. For the single-stressor experiment, eggs were reared at a wide range of ten constant temperatures (10 to 24 °C) and separated into starved and fed treatments groups after hatching. Response variables included embryo survival, embryonic period duration, larval size (instar-I), developmental and survival rates of instar-I larvae, and size after molting to instar II. For the multi-stressor investigation, larvae from a common environmental history as embryos were separated into eight constant CO₂ (~ 550 to 2,000μatm pCO₂) levels at two temperatures (18 or 22 °C). Larvae were maintained until molting into instar-II. Survival, developmental rate, and size at transition to instar-II larvae were quantified. It is expected that these variables will serve as bioindicators of the resilience of early life-stage horseshoe crab to changing climates.