The last generation: F3 of Echinometra sea urchins under experimental climate change

Abstract Ocean warming and acidification are a threat to calcifying marine invertebrates such as Echinoderms. Transgenerational plasticity may allow animals to respond to these conditions, but few studies exposing marine invertebrates to climate stressors over multiple generations exist. Here, data from the final ( F 2 post-settlement, F 3 larvae and juveniles) generations in a long-term (> 6 yrs) experiment on the tropical sea urchin Echinometra sp. A . This commenced with exposing wild collected animals ( F 0 generation) and subsequent generations (larvae and adults both for F 1 and F 2 ) to control (present-day ambient) and climate change (CC) conditions (2 °C above ambient temperatures, 940 ppm p CO 2 ). Survivorship in all F 2 treatments (ranging from all generations being held at ambient conditions to all at elevated conditions) was high (> 50%). Some significant differences in survivorship existed among treatments, although there was no apparent relationship to CC conditions exposure time. There was also no difference in size among treatment groups in the F 2 sea urchins up to 720d post-settlement. As in previous generations, the largest effect on adults was that males exposed to CC conditions have reduced reproductive potential, and there was a significant negative relationship with the number of generations exposed to future ocean conditions and spawning performance. Effects were extreme, in that we could only raise larvae from the control treatment, or those individuals kept for 0.5 generations (only F 2 adults under climate change conditions). Larvae from both parental groups only reached settlement when raised under control conditions. Larval morphology also responded to treatment (reduced arm length under CC conditions) and exhibited negative parental effects (smaller arm and body lengths from parents under CC conditions). Thus, negative parental effects observed in earlier publications did not diminish over the following generations but, in some traits, increased. We therefore detected no evidence of transgenerational acclimation to future ocean conditions.