The size dependence of sea star locomotion: Does bigger mean faster?

Abstract

As a general rule, larger-bodied animals within a species move at faster absolute speeds independently of locomotive mode. The relationship between body size and speed in sea stars is decidedly less clear. One species of sea star follows the general trend, three species show no correlation between body size and speed, and one species exhibits the opposite relation. To address these puzzling observations, I quantified body size, body shape, and crawling speed in four previously unstudied species of Northeast Pacific sea stars: the multi-armed stars Pycnopodia helianthoides and Solaster stimpsoni, and the fixed-arm number Dermasterias imbricata and Leptasterias hexactis. Only L. hexactis exhibited statistically significant allometries in arm width, arm length, and oral disk. When correlating measures body size with crawling speeds, larger individuals within the multi-armed species were faster - but larger individuals of fixed-arm species crawled slower. Crawling speed differences between plastic and fine sand differed among species.