To investigate the effects of elevated seawater p CO_2 on the early developmental stages of marine benthic calcifying organisms, we exposed the eggs and larvae of Argopecten irradias, an important bivalve species in Chinese aquaculture, in seawater equilibrated with CO_2-enriched(1000 ppm) gas mixtures. We demonstrated that elevated seawater pCO_2 significantly interfered with fertilization and larval development and resulted in an increased aberration rate. Fertilization in the treatment(pH 7.6) was 74.3% ± 3.8%, which was 9.7% lower than that in the control(p H 8.3)(84.0% ±3.0%). Hatching success decreased by 23.7%, and aberration rate increased by 30.3% under acidic condition. Larvae in acidified seawater still developed a shell during the post-embryonic phase. However, the shell length and height in the treatment were smaller than those in the control. The development of embryos differed significantly at 12 h after fertilization between the two experimental groups. Embryos developed slower in acidified seawater. Nearly half of the embryos in the control developed into D-shaped larvae at 48 h after fertilization, which were considerably more than those in the treatment(11.7%). Results suggest that future ocean acidification(OA) would cause detrimental effects on the early development of A. irradias. To investigate the effects of elevated seawater p CO_2 on the early developmental stages of marine benthic calcifying organisms, we exposed the eggs and larvae of Argopecten irradias, an important bivalve species in Chinese aquaculture, in seawater equilibrated with CO_2-enriched (1000 ppm) gas mixtures. The treatment of elevated seawater pCO 2 significantly interfered with fertilization and larval development and resulted in an increased aberration rate. Fertilization in the treatment (pH 7.6) was 74.3% ± 3.8%, which was 9.7% lower than that in the control (p H 8.3) (84.0% ± 3.0%). Hatching success decreased by 23.7%, and aberration rate increased by 30.3% under acidic condition. Larvae in acidified seawater still developed a shell during the post-embryonic phase. However, the shell length and height in the treatment were smaller than those in the control. The development of embryos differed significantly at 12 h after fertilization between the two experimental groups. Embryos develo Nearly half of the embryos in the control developed into D-shaped larvae at 48 h after fertilization, which were considerably more than those in the treatment (11.7%). Results suggest that future ocean acidification (OA) cause detrimental effects on the early development of A. irradias.