, 1997) could thereby be exacerbated, decreasing reproductive output in affected males. Conversely, reduced sperm swimming under acidified conditions could increase sperm longevity due to lowered consumption of limited endogenous energy provisioning ( Mita and Nakamura, 1998). Greater sperm longevity may increase chances of successful fertilization if sperm–egg-encounter rates remain sufficient over see more prolonged periods of time ( Levitan, 2000 and Marshall, 2002). Impacts of CO2-driven ocean acidification on

sperm swimming behavior of G. caespitosa may interact with other acidification impacts on fertilization variables such as male–female compatibility, egg competition or polyspermy block efficiency ( Evans and Marshall, 2005, Evans and Marshall, 2005 and Marshall and Bolton, 2007). Metabolism inhibitor Negative impacts of CO2-induced ocean acidification have also been

reported for later life-history stages of serpulid tubeworms, such as weaker calcareous tubes ( Chan et al., 2012 and Smith et al., 2013). Resultant cumulative effects on reproductive success and survivorship are likely to exacerbate the rate or intensity of selection pressure of climate change. Patterns of sperm swimming responses of G. caespitosa to CO2-induced acidification observed here were similar to those of Arenicola marina sperm in lowered seawater pH ( Pacey et al., 1994). Sperm activation in A. marina was delayed and sperm speed was reduced in HCl-acidified seawater (pH < 7.6). Interestingly, our findings are very different to those from Cediranib (AZD2171) a study on the related serpulid species Pomatoceros lamarckii ( Lewis et al., 2012). Sperm speeds of P. lamarckii were robust to CO2-induced pH reductions, percent motility was significantly reduced, but responses were non-linear. These findings may be explained by differences in experiment design and sample

size (5 pooled assays ( Lewis et al., 2012) vs 23 single individuals in this study). As outlined earlier, conducting adequately replicated studies will help to clarify whether these differences are caused by high inter-individual variability or differences in average responses between species. In conclusion, the substantial inter-individual variation in sperm responses observed here may ameliorate effects of future climate change, if the traits that drive phenotype robustness are heritable. Sperm from some G. caespitosa will be better equipped to cope with acidification than others, creating ‘winners’ and ‘losers’ in a future acidified ocean ( Schlegel et al., (2012). This observed resilience to near-future conditions could increase the potential for adaptation to far-future conditions, if gathering of advantageous alleles can occur quickly enough. Likewise, rapid selection against phenotypes susceptible to acidification may quickly reduce genetic diversity and lead to severe flow-on consequences for fitness and competitive ability downstream. Very few studies to date have investigated climate change impacts on polychaete species ( Chan et al.