Comparison of predatory behavior and drillhole characteristic between Rapana venosa and Glossaulax didyma

Abstract

In order to extract information about predators from the drillhole characteristics, predatory behavior, drillhole-site selectivity, and preference of prey size and species were examined in Rapana venosa and Glossaulax didyma. Laboratory experiments used predators and the prey bivalves collected from Lake Hamanako in Shizuoka Prefecture, central Japan. Glossaulax didyma always drilled around umbo of bivalve shell, and it preferred similar prey size to its shell size. In contrast, observation of predatory behavior of R. venosa revealed that this species usually killed prey bivalve without drillhole but left slit-shaped scratches or nomarks using probably poisoning or suffocation. Rapana venosa preferred the largest individuals among the different sizes of Ruditapes philippinarum, and it consumed first Cyclina sinensis rather than R. philippinarum and Scapharca kagoshimensis. Our results made clear the differences of the drillhole characteristics and preference of prey size between R. venosa and G. didyma, and enabled to suggest the predator species from the dead and fossil shell.