Organisms employ varying strategies to procure resources and defend themselves from competitors and potential predators. Decorating behavior, or attaching biotic and abiotic materials to the body, by majid crabs can potentially assist in this regard and may be influenced by factors such as algal substrate composition and social interactions among the crabs. To determine these potential functions and factors we created a baseline catalog of behaviors (ethogram) exhibited by the decorating crab Microphrys bicornutus. Decorating by this crab involved a complex set of behaviors that begins when a crab approaches an algal substrate, removes, then manipulates pieces resulting in the attachment of algae to specialized hooked setae on the exoskeleton of its body. In general, once decorated, the crab remained motionless on the substrate for considerable periods of time compared to other behavioral acts. In addition to the decorating behaviors exhibited when solitary, crabs were involved in limited agonistic behaviors during encounters with conspecifics. Specifically, crabs showed aggressive behaviors including active strikes and displays that apparently served as warning to conspecifics. Crabs also showed a concomitant decrease in motility (when not actively engaged with another individual) during these conspecific encounters. Such behaviors may help crabs maintain dispersed distributions around algal substrate sources thereby decreasing intraspecific encounters. Overall, data from these trials suggest that Microphrys bicornutus shows a generalist tactic and uses algae based on abundance rather than preference for an algal species. Decorating by these crabs, and others, provide excellent opportunities to explore community-level interactions in marine ecosystems.
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