The effects of density and size on the hiding response of Christmas tree worms (Spirobranchus giganteus)
Hiding is a common anti-predatory behavior that many organisms utilize. This anti-predatory tactic is adjusted to minimize factors such as lost time spent foraging and reproducing. Variation in hiding exists to minimize these costs while optimizing the benefit of predator avoidance. The hiding behavior of Christmas tree worms, Spirobranchus giganteus, was observed using an artificial stimulus to assess how density (number of individuals cm-2 ), existence within an aggregation or as a solitary individual, the nearest neighbor behavior, and body size affect the re-emergence time of the worms after hiding. This study also assessed the natural hiding responses of S. giganteus using videos. Individuals that were solitary had significantly longer re-emergence times than individuals that were part of an aggregation. These results emphasize the benefits of aggregated living in reducing the hiding time of Christmas tree worms. In aggregations, the re-emergence times of an indirectly stimulated individual increased with distance from the directly stimulated worm. These results could be indicative of a communication system within aggregations. Within these aggregations, reemergence times were consistent regardless of size whereas solitary individuals had significantly longer re-emergence times as the size of the worm increased. Variations in hiding times illustrate the importance of refined behavioral decisions in animals. Hiding behaviors of aggregated individuals could be a useful tool in studying community dynamics, specifically the existence and mechanisms of communication between individuals.