MEPS 619:35-51 (2019)  -  DOI: https://doi.org/10.3354/meps12950

ABSTRACT: Ocean acidification impacts many marine biota. Although evolutionary responses should occur during persisting environmental change, little is known about the adaptability of copepods. Therefore, we set up a 3½ yr long selection experiment, maintaining Acartia tonsa populations in seawater treated with 200 and 800 μatm CO₂, and feeding them with algae cultured under corresponding CO₂ conditions. In 3 reciprocal transplant experiments, roughly 1 yr apart, we measured developmental rates, C:N and C:P ratios, egg production and hatching rates of the different lines. In the transplant experiments, we observed significantly lower developmental rates in the high CO₂ treatment independent of the selective history. Egg production and hatching success were unaffected by the experimental conditions, but we observed an earlier hatching of eggs from females with a high CO₂ selective history. Over the experimental period, beneficial adaptations of the copepods cultured under high CO₂ conditions of elevated seawater pCO₂ and associated food quality were not detected. However, towards the end of the experiment, copepods cultured under elevated pCO₂ and fed with high CO₂ algae showed increased body mass and decreased prosome length.

KEY WORDS: Ocean acidification · CO₂ · Acartia tonsa · Adaptation · Body stoichiometry