Feeding Activity Patterns and Carrion Removal by Terrestrial Hermit Crabs at Enewetak Atoll, Marshall Islands

Terrestrial hermit crabs (Coenobita spp.) were observed feeding on a variety of food items corresponding with observations on the genus worldwide . A field experiment was conducted which examined (1) the feeding activity of Coenobita in two habitats and (2) their potential impact on the removal of carrion and on the colonization of carrion by fly maggots. Habitat and time of day influenced the size and species of Coenobita feeding. Large C. perlatus fed only at night and had the greatest impact on the carrion. Although small Coenobita had little effect on the carrion, their feeding activity did reduce the number offly maggots in the carrion. The scavenging activity of hermit crabs may serve a useful role on inhabited islets. The rapid removal of carrion would reduce potential fly breeding sites. TERRESTRIAL HERMIT CRABS, primarily Coenobita perlatus, C. rugosus, and C. brevimanus, are the principal native terrestrial fauna on many islets at Enewetak Atoll (11°30' N 162°10' E). Few studies are available concerning the feeding habits of these crabs, despite their great numbers on some islets (Page and Willason 1982), the alleged importance of hermit crab feeding activity to atoll terrestrial ecology (Niering 1956, 1963; Degener and Gillaspy 1955), and the potential importance of hermit crabs to man as consumers of carrion (Wiens 1962). Studies of the feeding habits of Coenobita have been confined primarily to observations of food items eaten (e.g., Seurat 1904, Ball 1972, De Wilde 1973, Alexander 1979). Little information is available concerning Coenobita feeding patterns or their potential impact on food resources. This study records natural food items eaten by Coenobita at Enewetak and compares these with observations on the genus worldwide. 1 This research was supported by the Mid-Pacific Research Laboratory, Enewetak Atoll, Marshall Islands, and the Marine Science Institute, University of California, Santa Barbara. Manusc ript accepted 121anuary 1983. 2 University of Californ ia, Santa Barbara, Marine Science Institute, Santa Barbara, California 93106. In addition, a preliminary field experiment was conducted to (1) examine hermit crab feeding activity patterns and (2) assess the impact that the feeding activity of hermit crabs might have on carrion removal and on the colonization of carrion by fly larvae . MATERIALS AND METHODS Notes were made on the types of food items eaten by Coenobita at two uninhabited southern islets, Mut and Ikuren, during September and October 1979. These islets were relatively undisturbed by man and had lush vegetation and large hermit crab populations (Page and Willason 1982). Preweighed amounts of raw chicken or reef fish (simulating natural carrion) were enclosed in cages on Mut Islet on 2 October 1979. The 25 x 25 x 25-cm cages were constructed of 5-mm mesh galvanized screen and were sunk 10em into the ground. Carrion was secured to a stake driven through the center of each cage. Chicken and fish were used at beach stations, which were located on sand slightly above the mean high water mark on the lagoon side of the islet. At the interior station, located 30 m inland in a Pisonia Cocos forest, only chicken was used . Three experimental treatments were estab-