Low pH Does Not Impact Reproductive Success but Leads to Negative Carry-Over Effects Between Parents and Larvae in a Mediterranean Gastropod

Understanding how marine organisms respond to ocean acidification across all life stages is essential for assessing the future resilience of ecosystems. We investigated the effects of long-term exposure to low pH conditions (pH_T ranging from 7.95 to 7.22) on the reproductive traits and intracapsular development of Hexaplex trunculus, a predatory Mediterranean gastropod. Spawning success, fecundity, and capsule morphology were not affected by pH. However, larval development was significantly impaired at pH_T lower than 7.51, with observed delayed development and fewer larvae developing successfully to the hatchling stage. Cross-transplantation of spawns between pHs indicated a negative carryover effect of parental exposure to low pH on larval development, although this was partially reversible when spawns were transferred back to the ambient pH. Notably, we observed inter-individual variability in larval growth, suggesting that phenotypic plasticity or genotype-specific tolerance may play a role in moderating sensitivity to future ocean acidification. Our study highlights the importance of considering parental exposure, natural pH variability, and within-population variation when assessing species responses to global drivers.