Growth rates and planktonic development periods of marine invertebrate larvae have important consequences for the ecology of marine invertebrates. The growth and development of the larvae of a common southern Australian polychaete was examined to determine whether it was limited by natural concentrations of planktonic food, and whether naturally occurring variation in maternal investment in offspring influenced larval growth and development. Larvae that were provided concentrated diets of natural planktonic food were larger than larvae that were provided with food at ambient concentrations, but both experimental groups of larvae reached developmental stages immediately preceding settlement at the same time. Thus, larval growth was limited at natural concentrations of planktonic food but larval development rates were unaffected. These trends were also apparent in larvae fed with different concentrations of laboratory cultured food. Maternal investment in offspring (eggs) was higher on average for larger females than for smaller females. Larvae developing from smaller eggs were also smaller before settlement than larvae developing from larger eggs. Both maternal investment in offspring and the extent to which larval growth is food limited may vary spatially and seasonally along the southern coastline of Australia owing to the yearly occurrence of nutrient-rich oceanographic upwellings.