Snail Predation by Hemigrapsus nudus and Hemigrapsus oregonensis: Sex and Species Differences in Chela Size

Abstract

The relationship between propus size and use of snails as prey in sympatric populations of Hemigrapsus nudus and Hemigrapsus oregonensis was investigated. Propal height and propal width increases with body size in a predictable manner in male and female crabs of both species. Sexual dimorphism of propal height and width relationships in both shore crabs is apparent, but there was no detectible difference in chela size between H. nudus and H. oregonensis. The lack of difference in chela size between sympatric H. nudus and H. oregonensis suggests that there is no character displacement in this trait. Both species of crabs showed a strong feeding preference for the thin-shelled gastropod Lacuna vincta over the thicker shelled Littorina scutulata, likely due to the ease of consumption. There were no differences in snail consumption rates between male and female H. nudus of similar propal heights, mostly due to high feeding variation among individual crabs.