Some factors influencing predation by the flatworm,Stylochus ellipticus (Girard), on oysters
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Some of the effects of low temperature, low salinity, prey size, and predator source on the predatory activity ofStylochus ellipticus on oysters were investigated in the laboratory.
Lowering temperatures below 10 C resulted in a progressive decrease in predation. Salinities as low as 5‰, approximately the lower limit of tolerability of the oysters, appeared to give no lasting decrease in predation. As an oyster predator,S. ellipticus primarily attacked small individuals but large worms (20 mm long) killed oysters as long as 61 mm.
S. ellipticus from seven localities were observed in the laboratory for differences in predatory activity on oysters and barnacles. An obvious preference for one or the other prey species was demonstrated by worms from each locality. Worms from higher salinities preferred barnacles, whereas those from lower salinities preferred oysters. Prey preference might be correlated with a comparatively greater abundance of barnacles in higher salinities and oysters in lower salinities. This relationship could be consistent with the hypothesis of “ingestive conditioning,” which states that a predator develops a tendency to respond more readily to effluents from a given invertebrate prey species after ingestion of living tissues of that species.
KeywordsPrey Species Prey Size Prefer Prey Predatory Activity Oyster Spat
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