Offspring size and performance in variable environments: field studies on a marine snail

This study links offspring size and energetic content to offspring performance (measured as growth and survivorship) in the intertidal gastropod Nucella ostrina and examines the effect of hatching size on performance at different times of year and in contrasting environments. The relationships between individual hatchling size and organic content were compared both within and among clutches of N. ostrina. Hatchling size was positively, significantly, and predictively correlated with hatchling organic content both within and among clutches, demonstrating that hatching size could be reliably used as an indicator of maternal investment. The slope of the relationship between hatchling size and organic content varied between clutches, suggesting intrapopulation variation in embryonic growth geometry. In field outplants, hatching size always had a positive and significant effect on growth, and small hatchlings took approximately one month to reach the initial size of their larger siblings. More large hatchlings than small hatchlings were recovered in every experimental outplant. The effect of hatching size on recovery was not significant in short (9 d) outplants, but recovery of large hatchlings was significantly greater than recovery of small hatchlings in two out of three long‐term (36 or 54 d) outplants. Overall recovery was lower in the summer, the long‐term outplant in which size did not significantly affect recovery. In experiments testing the relationship between hatching size and survivorship in two environments that differed in degree of sun exposure, size significantly and positively affected recovery in the more shaded habitat (with higher overall recovery) but not in the sun‐exposed environment. Thus, larger hatching size in N. ostrina results in (1) increased hatchling growth, (2) considerably shortened time to maturity, and (3) higher survivorship. However, the advantage of large hatching size was decreased under more severe environmental conditions, those which resulted in higher overall hatchling mortality. Contrary to predictions, poor environmental conditions may not be more likely to select for large offspring size in intertidal habitats: during periods of high heat stress, mortality may be largely random with respect to size.