Prevention of Shell Burial as a Benefit Hermit Crabs Provide To Their Symbionts (Decapoda, Paguridea)

Abstract

symbionts incur through their association with hermit crabs. However, as Ross & Sutton (I96I) have pointed out, most of the proposed benefits have been inferred and not demonstrated. Furthermore, these particular benefits will vary depending on the species of hermit crab and symbiont. Shelter or protection from predators (Orton, 1922) and greater ease in acquir ing food are the most commonly proposed benefits. Associating with a hermit crab could help the symbionts acquire food in various ways depending on the species involved. The sea anemone, Adamsia palliata (Bohadsch), is actually fed by the hermit crab, Pagurus prideauxi Leach (cf. Fox, 1965). The polychaete, Nereis fucata (Savigny), is able to steal food from the hermit crab by placing its pharynx between the third maxillipeds of the crab (Brightwell, 1951). Other symbionts, such as the hydroid, Hydractinia echinata (Fleming) (cf. Schijfsma, 1935; Wright, 1973), and various sea anemones (Balss, 1924) share in the crab's meal by passively waiting for pieces of food to come into contact with them. While there has been some question as to how much food these symbionts actually acquire in this manner, the hermit crabs do provide mobility that presumably enhances the symbionts' chance of finding food (Balss, 1924; Ross, I960; Ross & Sutton, I96I; Jensen, 1970; Wright, 1973). Still other benefits have been suggested besides protection and food. From observations made on aquarium specimens, Wright (1973) concluded that the hermit crab's movement and respiratory current would help keep Hydractinia echinata free of sediments. Balss (1924) suggests that one benefit of the hermit crab's movement is in providing the symbionts with oxygen-rich water. Although specific benefits to particular organisms undoubtedly occur, the study reported here suggests that at least in the temperate sand littoral zone, a general benefit provided by hermit crabs is to keep the shells and associated organisms from being buried by sand. The study was conducted from October, 1972 through March, 1973 in Tampa Bay at St. Petersburg, Florida. To obtain a measure of the incidence of the burial of gastropod shells un occupied by hermit crabs, the openings of some shells were sealed to prevent entry by hermit crabs. The shells were placed in small groups at various locations within