Sea Star Acrobatics: Testing the Righting Response of Eight Different Asteroid Species on Two Different Substrata

Abstract

Sea stars typically live with their oral side facing the substratum, and the ability to right themselves when turned over is important response to avoid desiccation and predation. The righting time of 8 species of sea stars; Henricia leviuscula (3 color variations), Henricia pumila sp. nov., Leptasterias hexactis, Pyconopodia helianthoides, Pisaster ochraceus, and Pteraster tesselatus were tested on two different substrata to determine if it affects righting time. The righting times were measured when sea stars were placed with their aboral side on the substratum in two different tanks, one covered with sand and another with no sediment. Since podia adhesion to the substratum is required for a sea star to right itself, it was expected that substrata with a smaller grain size would cause an increase in righting time compared to a flatter surface. Sea star diameter was measured to determine the correlation between size and righting time. Leading arm identification was also observed to test the initiating arm preference. P. tesselatus was the only species that was unable to right itself in sand. In most species, sand increased the average righting time compared to other substrata. Individuals with a larger diameter were found to have an increased righting time. No significant relationship was found to which arm initiated the response in all individuals. This study helps to add to the minimal knowledge of this unusual behavior of echinoderms.