To predict effects of global change on marine populations, it is important to measure the effects of climate stressors on performance and potential for adaptation. Adaptation depends on heritable genetic variance for stress tolerance being present in populations. We determined effects of near-future ocean conditions on fertilisation success of the sea urchin Pseudoboletia indiana. In 16 multiple dam-sire crosses, we quantified genetic variation in tolerance of warming (+3°C) and acidification (-0.3-0.5 pH units) at the gastrulation stage. Ocean acidification decreased fertilisation across all dam-sire combinations with effects of pH significantly differing among the pairings. Decreased pH reduced the percentage of normal gastrulae with negative effects alleviated by increased temperature. Significant sire by environment interactions indicated the presence of heritable variation in tolerance of stressors at gastrulation and thus the potential for selection of resistant genotypes, which may enhance population persistence. A low genetic correlation indicated that genotypes that performed well at gastrulation in low pH did not necessarily perform well at higher temperatures. Furthermore, performance at fertilisation was not necessarily a good predictor of performance at the later stage of gastrulation. Southern range edge populations of Pseudoboletia indiana may benefit from future warming with potential for extension of their distribution in south east Australia.