The blue bat star Patiria pectinifera was long considered a slow-moving grazer but is in fact a predator capable of catching agile animals. A research group led by Graduate Student Haruto Gushiken and Professor Satoshi Wada of the Graduate School of Fisheries Sciences at Hokkaido University has shown that P. pectinifera found in Hakodate Bay exhibit a previously unknown behavior referred to as "standing-on-tiptoe," and this behavior is a foraging technique to capture crabs, which move faster than the starfish. The findings were published in Plankton and Benthos Research.
(A) A focal individual in its general posture with tube feet attached to the glass wall and the edge of its central disk sealed against the glass wall or slightly raised.
(B) Only the tips of the arms are touching the glass wall, and the central disk has pulled away from the glass wall (standing-on-tiptoe state). The white arrow points to a shore crab about to enter the space between the disk and the aquarium wall.
(C) A shore crab (white arrow) has entered the space below the uplifted disk and the lifted edge has been lowered and adheres to the glass.
(D) The starfish pressing its stomach against and feeding upon the captured crab.
Provided by Hokkaido University
Patiria pectinifera is a familiar starfish widely found in Japan and is also displayed in touch pools and other facilities of aquariums throughout Japan. This starfish is known to be a cleaner of the sea, which feeds on seaweed, small organisms on the seaweed and detritus by pressing its everted stomach against them. Because it moves slowly, no previous studies have been conducted with the assumption that it preys on agile organisms such as crabs. However, upon closer examination of P. pectinifera feeding on at the beach, starfish feeding on crabs were observed multiple times.
In this study, the research group verified the behavior of P. pectinifera to capture crabs in laboratory experiments. The following two experiments were conducted using wild-caught P. pectinifera and Gaetice depressus individuals. In Experiment 1, the starfish behavior was video-recorded for 99 hours using a 1-second time lapse in an aquarium with one starfish and five live crabs (live-crab condition) and an aquarium with one starfish alone (no-crab condition). In Experiment 2, the starfish behavior was video-recorded for 99 hours using a 1-second time lapse in an aquarium with one starfish and five live crabs as in Experiment 1 (live-crab condition) and an aquarium with one starfish and one dead crab (dead-crab condition). Although the live-crab condition in Experiment 1 was the same as that in Experiment 2, different starfish individuals were used in the respective experiments.
Based on the video recordings, the research group collected data on the crab-eating behavior (standing-on-tiptoe behavior) of P. pectinifera under each condition and compared the number of starfish that engaged in the standing-on-tiptoe behavior between the conditions. In the recorded videos, the starfish were observed to raise their central disk (the center of the star shape), with only five arms (each tip of the star shape) being attached to the aquarium (standing-on-tiptoe behavior), and when a crab entered the space under the disk, they lowered the raised disk and captured the crab. Furthermore, in Experiments 1 and 2, the standing-on-tiptoe behavior was observed more frequently under the live-crab condition than under the no-crab and dead-crab conditions. These data indicate that P. pectinifera engages in the standing-on-tiptoe behavior more frequently when live crabs are present.
The results of this study disprove the common belief that P. pectinifera cannot prey on agile organisms like crabs and reveal that it is indeed an ingenious predator. A number of marine invertebrates are known to be slow movers, such as P. pectinifera. The results are expected to contribute to the advancement of research on the behavior which slow-moving organisms engage in to prey on fast-moving organisms.
Journal Information
Publication: Plankton and Benthos Research
Title: "Standing on tiptoe": A novel foraging technique in the starfish Patiria pectinifera
DOI:10.3800/pbr.19.84
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.