Differences in resource allocation to reproduction across the intertidal-subtidal gradient for two suspension-feeding marine gastropods: Crepidula fornicata and Crepipatella peruviana

The sedentary, suspension-feeding gastropods Crepidula fornicata and Crepipatella peruviana can be found in large numbers both subtidally and intertidally. Although intertidal animals often show reduced reproductive output compared with that of subtidal animals, we know little about how the reproductive output of marine gastropods is affected by exposure to intertidal stresses. We documented reproductive characteristics for intertidal and subtidal Crepidula fornicata in Rhode Island, USA (2012, 2013), and Crepipatella peruviana from Pelluco Beach, Chile (2010-2012). Females of both species brood encapsulated embryos for at least several weeks before releasing offspring, facilitating determinations of individual fecundity (embryos per egg mass). As expected from the environmental stresses experienced uniquely by intertidal individuals while emersed, including an inability to feed, intertidal females of C. peruviana had lower fecundities, producing significantly fewer egg capsules per brood; the mean number of eggs per capsule did not differ significantly by habitat. In marked contrast, the size-adjusted fecundity of Crepidula fornicata was significantly higher for intertidal females than for subtidal females; however, rather than brooding more egg capsules per individual or making larger egg capsules, intertidal females crowded each capsule with significantly more eggs. This study adds to previous work showing how exceptionally well-adapted C. fornicata is to intertidal life, and may help to explain why this species has been so unusually successful as an invasive among calyptraeid gastropods. Future studies will be required to identify the specific conditions that have provoked these adaptations in C. fornicata, and to understand the mechanisms through which this species achieves them.