ABSTRACT. – Ocean acidification due to anthropogenic emissions of CO₂ is the new kid on the block of climate change research and has received considerable attention as changes in seawater acidity and carbonate chemistry can severely affect marine organisms from the species to the ecosystem level. The degree of sensitivity within a species can vary greatly along ontogeny, often leading to highest sensitivities in early life stages. Recent studies using the cuttlefish Sepia officinalis, demonstrated that it’s oviparous developmental mode can constitute an additional challenge for early life stages as increases in environmental pCO₂ add on top to the already high CO₂ concentration inside the egg. The micro-environment inside the egg is characterized by low pH, hypoxia, hypercapnia and high ammonia concentrations as a result of the animal’s metabolism and the limited diffusion permeability of the egg capsule. This oviparous developmental mode in combination with lower pH regulatory capacities are probably the major reasons why S. officinalis embryos respond more sensitively towards seawater acidification compared to adults. Although stronger hypercapnia levels (> 0.3 kPa; < pH 7.5) could demonstrate potentially negative effects on the development, metabolism and calcification, acidification levels as predicted for the coming century will probably not severely affect S. officinalis. This relative tolerance may be a consequence of a lifestyle in benthic coastal habitats, pre-adapting S. officinalis to natural fluctuations in environmental pCO₂.