Ocean acidification impact on ascidian Ciona robusta spermatozoa: New evidence for stress resilience

Rising atmospheric CO₂ is causing a progressive decrease of seawater pH, termed ocean acidification. Predicting its impact on marine invertebrate reproduction is essential to anticipate the consequences of future climate change on species fitness and survival. Ocean acidification may affect reproductive success either in terms of gamete or progeny quality threating species survival. Despite an increasing number of studies focusing on the effects of ocean acidification on the early life history of marine organisms, very few have investigated the effects on invertebrate gamete quality. In this study, we set up two experimental approaches simulating the ocean conditions predicted for the end of this century, in situ transplant experiments at a naturally acidified volcanic vent area along the Ischia island coast and microcosm experiments, to evaluate the short-term effects of the predicted near-future levels of ocean acidification on sperm quality of the ascidian Ciona robusta after parental exposure. In the first days of exposure to acidified conditions, we detected alteration of sperm motility, morphology and physiology, followed by a rapid recovery of physiological conditions that provide a new evidence of resilience of ascidian spermatozoa in response to ocean acidification. Overall, the short-term tolerance to adverse conditions opens a new scenario on the marine species capacity to continue to reproduce and persist in changing oceans.