Effects of bivalve shell morphology on prey selection by predatory gastropods Rapana venosa (veined rapa whelk, Muricidae) and Laguncula pulchella (Asian moon snail, Naticidae) in temperate estuaries

Prey selection by two predatory gastropods, the whelk Rapana venosa and moonsnail Laguncula pulchella, which differ in feeding strategies, was experimentally examined using six infaunal bivalves (Mactra veneriformis, Moerella rutila, Macoma incongrua, Ruditapes philippinarum, Cyclina sinensis and Meretrix lusoria) and a sessile bivalve Crassostrea gigas, with varying shell morphologies. Both gastropods actively fed on three thin-shelled species (M. veneriformis, M. rutila, and M. incongrua), which required shorter handing times, indicating a preference for low-cost prey. In contrast, the thick-shelled M. lusoria was consumed infrequently by both gastropods due to its longer handling time. However, despite having a thin shell, C. sinensis was not actively preyed upon, likely because its inflated shell shape prevented R. venosa from effectively chipping the shell edge and hindered L. pulchella from fully wrapping the shell with its foot. These results suggest that prey selectivity depends not only on shell thickness but also significantly on shell shape and handling constraints associated with gastropod feeding mechanisms. Furthermore, the two gastropods differed in their ability to exploit sessile bivalves; R. venosa consumed C. gigas despite the longer handling time, whereas L. pulchella did not attempt predation. This suggests that the muricid gastropods, represented by R. venosa, have a broader prey range compared to the naticids. Overall, this study highlights the complex interplay between prey morphology and predator feeding strategies in determining prey selectivity among marine gastropods.