Evidence that rising coastal seawater temperatures increase reproductive output of the invasive gastropod Crepidula fornicata

Although water temperature is thought to be an important factor in the proliferation of the invasive slipper limpet Crepidula fornicata along the northern European Atlantic coast, evidence for this proposition is scarce. We used quantitative histology to compare the reproductive dynamics over 2 temporally-separated sexual cycles (2000-2001 and 2006-2007) from the same C. fornicata population in Bourneuf Bay, France. Water temperature and chlorophyll (chl) a data were also analyzed in relation to historical trends and to reproductive processes. Historical temperature data show a progressive warming trend, especially since 1995, when the slipper limpet problem began to be severe. Similarly, the incidence of high chl a peaks increased markedly from 1996 onwards. Significantly higher water temperatures and more chl a peaks were found for the 2006-2007 sampling period compared to 2000-2001, and corresponded to (1) an increase in duration of brood presence, most notably the appearance of broods earlier in the year, and (2) an increase in intensity of gametogenesis in 2006-2007. These results support the hypo thesis that increased Northern European water temperatures enhance the reproductive success of C. fornicata, both through more favourable gametogenic/brooding temperatures and through enhanced phytoplankton availability.