The response specificity of the Atlantic drill was further investigated to determine which cue sources (i.e., predator or prey) were eliciting these defenses. Neither species of drill uses a density-dependent risk assessment, as the effect of predation effluent was similar at both high and low densities of conspecific drills. This is consistent with an adaptive behavioral response and has the potential to transmit large positive indirect NCEs of the crab to oysters. In the presence of chemical effluent from crabs eating conspecifics, drills increased hiding behavior by 2 to 6 times, and reduced the number of oysters consumed by 50 to 67%. I investigated the consumptive (CEs) and non-consumptive effects (NCEs) of a native crab predator (the red rock crab, Cancer productus) on a system of two invasive oyster drills (the Atlantic drill, Urosalpinx cinerea, and the Japanese drill, Ocinebrina inornata), a native oyster (the Olympia oyster, Ostrea lurida), and an introduced but commercially valuable oyster (the Pacific oyster, Crassostrea gigas).
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