Abstract
ABSTRACT The Olympia oyster (Ostrea lurida)‡ was historically abundant in Willapa Bay, WA, but populations were decimated by overexploitation in the mid to late-1800s and have failed to recover. We investigated the potential role of two introduced predatory gastropods, the Japanese drill (Ocinebrina inornata) and the eastern drill (Urosalpinx cinerea), in limiting Olympia oyster recovery. We quantified the bay-wide distribution, local abundance, and per capita effects of drills, and asked how each of these three components of total invasion impact might be influenced by another dominant introduced species, the Pacific oyster (Crassostrea gigas). Bay-wide sampling revealed differences in spatial distribution of the two drill species, with U. cinerea more abundant toward the head of the estuary and O. inornata more abundant toward the mouth. Individual feeding trials indicated that both drill species preferred Pacific oysters to Olympia oysters of similar size, and preferentially attacked smaller oysters. W...
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