Nest-building behavior by the amphipod Peramphithoe femorata (Kroyer) on the kelp Macrocystis pyrifera (Linnaeus) C. Agardh from Northern-Central Chile.

Many small arthropod herbivores from terrestrial and marine environments construct tubicolous nest-like domiciles on their host plants or algae by rolling up selected portions of the leaf or blade. Nests serve as both shelter and food, which results in conflicting needs for the grazers because feeding activity continuously destroys parts of the nests. While the nesting habit of ampithoid amphipods and other peracarid crustaceans is widely known, very little is known about the nest dynamics and how the conflict between shelter and food requirements is resolved. Herein we examined the nest-building behavior and nest occupancy of the kelp-dwelling amphipod Peramphithoe femorata on the giant kelp Macrocystis pyrifera. Domiciles on the distal-most part of the blades were occupied by amphipods and were steadily advanced toward the blade base. Since the blades grow from a basal growth meristem, blades and nests develop in opposite directions. Thus, the amphipods exploit the kelp growth pattern to maintain their nests in the medium-distal part of the blades. During a 2-week-long experiment, we observed that blade elongation equaled nest advancement during the first 8 days after nest construction. Thereafter, blade growth slowed down and was surpassed by nest advancement rates, possibly forcing amphipods to seek out new blades. Nest occupancy was generally short (1-4 days), but some amphipods resided longer (>4 days) in their nests. The sophisticated nest-building behavior of P. femorata and other ampithoids maximizes nest persistence, offers optimal protection against predators, and promotes feeding on nutritive or, alternatively, on less defended tissues.