Starfish Capture Crabs by Standing on Tiptoe without Apparent Attractive Signaling

Predator–prey interactions are strongly influenced by the relative mobility of the two parties, as mobility determines the strategies available to predators. Predators that are slower than their prey often rely on alternative strategies, such as mimicking non-threatening objects or actively attracting prey. The blue bat star Patiria pectinifera uses a distinctive “standing-on-tiptoe” posture to capture the crab Gaetice depressus, a species that moves faster than the starfish. To investigate whether P. pectinifera uses signals that attract crabs, we observed crab behavior toward starfish exhibiting the tiptoe posture with their behavior toward a slowly elevated stone tile. If starfish use signals, crabs are expected to enter beneath starfish more frequently than beneath a stone tile. Unfortunately, although there are several differences in the experimental conditions between the two treatments, in stone-tile trials, 10 of 25 crabs (40%) entered the space beneath the tile, whereas in starfish trials, 10 of 30 crabs (33%) entered the space beneath the starfish. These results imply that starfish in the tiptoe posture might not lure crabs by using attractive signals. In this context, the tiptoe posture of P. pectinifera might represent a form of aggressive masquerade primarily operating in a predatory context.