Patterns of Limb Loss in the Blue Crab, Call/nectes Sap/dus Rathbun, and the Effects of Autotomy on Growth

A substantial proportion of the blue crab (Calfinecles sapidus Rathbun) population in a subestuary of the Chesapeake Bay was either missing or regenerating at least one limb in 1986 (24.8%) and 1987 (18.8%). Most crabs were missing a single cheliped; loss of four or more limbs was rare. Between June and November 1987, laboratory experiments were conducted in which one cheliped or both chelipeds and two pereopods were removed from blue crabs to examine the long-term effect of autotomy on growth and molting frequency. Crabs with all appendages intact served as controls. Loss of a single cheliped did not alter the molt increment, percent wet weight increase, or molting frequency of crabs compared to animals experiencing no limb loss. Multiple limb loss, however, significantly reduced the molt increment and percent weight increase in the first post-autotomy molt but did not affect the duration of the interrnolt. By the second molt following autotomy, molt increments for crabs missing four limbs did not differ significantly from those of intact or singly autotomized animals. Regenerating limbs were 85-88% of the lengths of undamaged, contralateral limbs in the first molt following autotomy. Up to three molts were required to regenerate 100% of the contralateral limb length. Removal of the major, crusher cheliped in both single and multiple autotomy treatments resulted in crabs possessing two minor, cutter claws after regeneration. Crabs failed to regenerate a distinct crusher even after three molts following autotomy. Although multiple autotomy reduced the molt increment in laboratory experiments, the rarity of severe limb loss in the Rhode River indicates that growth in the population is not affected greatly by autotomy. Autotomy refers to the reflex severance of a limb or other body part at a preformed breakage plane (Wood and Wood, 1932; Bliss, 1960; McVean, 1982). Many taxa (e.g., lizards and ophiuroids) can autotomize varying fractions of body parts (Sheppard and d' A. Bellairs, 1972; Wilkie, 1978; Bowmer and Keegan, 1983) and are capable of continuous regrowth of the missing structure (Congdon et a1., 1974). Crustacean autotomy responses differ in that autotomy involves loss of the entire limb. Furthermore, because growth in crustaceans is a discontinuous process, appendages can be replaced only by molting. The cost of autotomy for crustaceans, therefore, could be high since these animals must survive one or more molt cycles before an appendage can be regenerated completely. Crustacean growth is dependent upon the duration of the intermolt (molt interval) and the size increase at each molt (molt increment) (Hartnoll, 1982). The diversion of metabolic resources to regenerate autotomized appendages obviously could affect growth, and limb autotomy has been shown to reduce size increase at the molt in Cancer pagurus (Bennett, 1973), Hemigrapsus oregonensis and Pachygrapsus crassipes (Kuris and Mager, 1975), Uca pugilator (Hopkins, 1982), and Callinectes sapidus (Ary et a1., 1987). Effects oflimb loss appear to be additive, such that the molt increment decreases proportionally as increasing numbers of limbs are lost (Bennett, 1973; Kuris and Mager, 1975). The effect of limb autotomy on the molt interval is complex and depends on the stage in which the limbs were lost and the number oflimbs removed. Multiple limb loss before a critical preparatory stage (probably early pro ecdysis, Do; Skinner and Graham, 1972) either hastened the next ecdysis (Skinner and Graham, 1970;