The mode of dislocation of Astropecten aranciacus

Abstract

1. The mode of dislocation of the sea star Astropecten aranciacus was investigated on 23 individuals at the NE-coast of Sardinia. All were small to medium-sized representatives of the species; their radius (R) varied between 5 and 15 cm. The observations were carried out on 2 level sediments with different sand-grain diameter. Each sea star was followed for 30 min and its locations were recorded every minute. 2. A. aranciacus does not move continuously. It stops intermittently for an average duration of 2 minutes. On coarse grained sand, stops occur more frequently than on fine grained sand. 3. The average distance travelled in 30 min was 3.7 m on fine sand, 1.6 m on coarse sand. Including the stops, the cruising speed varied mostly between 0 and 20 cm/min on fine sand, and between 0 and 10 cm/min on coarse sand. 4. Generally, the observed paths were all or partially straight. In accord with this, the ratio W/D between the distance travelled (W) and the shortest between the starting and end position (D) was smaller than 2 for most animals. 5. Small ripple marks (on fine sand) do not seem to influence the direction of dislocation. Single observations indicate, however, that more pronounced ripple marks (on coarse sand) may have an influence. © 1973 Biologischen Anstalt Helgoland.