Laboratory studies showed that, given equal abundance of the two limpet species, Collisella pelta Rathke was consumed more often than Notoacmea scutum Rathke by the seastar, Pisaster ochraceus Brandt. The difference in consumption between limpet species appeared
to be a function of ability to avoid capture. Laboratory studies showed that N. scutum could outrun the seastar but C. pelta could not. N. scutum has longer cephalic tentacles than C. pelta which appeared to allow an earlier tactile warning of the seastar's presence.
Both species were able to sense the seastar at a distance, but they responded differently. N. scutum tended to move away from the predator but C. pelta merely moved a greater distance in the direction it was originally facing. C. pelta is most abundant in the upper intertidal
while N. scutum and P. ochraceus are most abundant in the lower intertidal. With better escape mechanisms, N. scutum should be more able to coexist with the seastar than C. pelta and it is suggested that predation pressure may be a possible explanation for the vertical
distribution of the limpets.
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