UNH URC 2020 - Green sea urchins need friends: Decision making and risk in Strongylocentrotus droebachiensis in competitive and non-competitive foraging environments
From Sierra Rose Walsh
Green sea urchins (Strongylocentrotus droebachiensis) have unique foraging behaviors not currently understood. Pilot studies have examined these behaviors with captive urchins and have noted that competition may change urchin foraging behaviors. We ran experimental trials on green sea urchins to investigate behavior of solitary and groups of urchins when offered a high value food source (shrimp). Urchins were placed in one of two environments: competitive (five urchins total) or non-competitive (alone), with three replicates of each in three types of experimental trials. The base of these trials involved timing the urchins’ movement across a tank from a uniform starting point to an animal protein food source, rewarding the urchins with some of the animal protein once the food was reached within the trial duration; we also recorded a lack of results within each trial. The three trial types involved the urchins being able to use kelp as cover and a food source during the trial, have no cover, or use mussel shells for cover but not as food. Over the course of the trials, trade offs among attraction of the food source, competition, and refuge from potential predation were observed. Solitary urchins more frequently favored any type of refuge than urchins in competitive environments despite the high value food source, which were more likely to access the food within the allotted time, and to access the food quicker, suggesting a competitive effect. These results indicate that urchins make riskier decisions when in groups.