Little is known of the capacity that marine metazoans have to evolve under rapid pCO2 changes. Consequently, we reared a marine polychaete, Ophryotrocha labronica, previously cultured for approximately 33 generations under a low/variable pH regime, under elevated and low pCO2 for six generations. The strain used was found to be tolerant to elevated pCO2 conditions. In generations F1 and F2 females' fecundity was significantly lower in the low pCO2 treatment. However, from generation F3 onwards there were no differences between pCO2 treatments, indicating that trans-generational effects enabled the restoration and maintenance of reproductive output. Whilst the initial fitness recovery was likely driven by trans-generational plasticity (TGP), the results from reciprocal transplant assays, performed using F7 individuals, made it difficult to disentangle between whether TGP had persisted across multiple generations, or if evolutionary adaptation had occurred. Nonetheless, both are important mechanisms for persistence under climate change. Overall, our study highlights the importance of multi-generational experiments in more accurately determining marine metazoans' responses to changes in pCO2, and strengthens the case for exploring their use in conservation, by creating specific pCO2 tolerant strains of keystone ecosystem species.

In order to allow full comparability with other ocean acidification data sets, the R package seacarb (Gattuso et al, 2015) was used to compute a complete and consistent set of carbonate system variables, as described by Nisumaa et al. (2010). In this dataset the original values were archived in addition with the recalculated parameters (see related PI). The date of carbonate chemistry calculation is 2016-11-09.