IMIS

Individually marked Japanese oyster drills, Ocinebra japonica, were presented with a choice of four different food organisms: mussels (Mytilus edulis); clams (Venerupis japonica); and oysters (Crassostrea gigas and Ostrea lurida). During the course of the 65-day experiment mussels constituted 42.6 per cent of the food organisms attacked by drills; clams, 36.5 per cent; and oysters, 20.9 per cent. The average time that an Ocinebra took to drill though a shell and finish feeding on the body mass are: mussels, 4.98 days; clams, 6.31 days; Olympia oysters, 5.70 days; and Pacific oysters, 14.0 days (on the basis of one Pacific oyster). Experimental evidence suggests that a drill will continue to attack the same species of food organism that it had attacked previously, rather than moving to an easily accessible organism of a different species.