EFFECTS OF MERCURY, CADMIUM, 



AND LEAD SALTS ON 



REGENERATION AND ECDYSIS IN 



THE FIDDLER CRAB, UCA PUGILATOR 



Crabs are capable of autotomizing injured limbs at 

 a preformed breakage plane and subsequently re- 

 generating them. The regenerating limb bud 

 grows in a folded position within a layer of cuticle, 

 and unfolds when the animal molts. The length of 

 regenerating limb buds is generally expressed in 

 terms of "R-value" (Bliss 1956) which is length of 

 limb bud x 100/carapace width. Such a regenera- 

 tion index is useful for comparisons of crabs of 

 different sizes. Since regeneration always termi- 

 nates with a molt, the presence of regenerating 

 limbs can affect the timing of ecdysis, and factors 

 which influence ecdysis will also affect regenera- 

 tion. For example, removal of eyestalks, a source 

 of molt-inhibiting hormones, is a standard way of 

 inducing precocious molting. Such animals will 

 regenerate missing limbs rapidly, but will gener- 

 ally die at ecdysis. Skinner and Graham (1972) 

 have shov^Ti that multiple autotomy, producing 

 many regenerating limb buds, can cause acceler- 

 ated regeneration, also leading to precocious molt. 



Heavy metals as pollutants of the marine envi- 

 ronment are of great concern. These chemicals are 

 released as a result of industrial processes and 

 tend to be toxic and to accumulate in organisms. 

 Their toxicity to Crustacea has been studied by 

 Corner and Sparrow (1957), Wisely and Blick 

 (1967), Eisler (1971), Vernberg and Vernberg 

 (1972), and O'Hara (1973). 



This paper reports on the effects of mercury, 

 lead, and cadmium on regeneration in the fiddler 

 crab, Uca pugilator. With its estuarine intertidal 

 habitat, this crab is likely to be subject to heavy 

 metal pollution in industrial areas. 



Materials and Methods 



Fiddler crabs were collected in July and August 

 from Accabonac Harbor, near East Hampton, 

 N.Y., and brought into the laboratory. Autotomy 

 of one chela and six walking legs was induced by 

 pinching each merus with a hemostat. Im- 

 mediately after autotomy, crabs were placed in 

 solutions of Pb(N03)2 (Reagent grade, Fisher Sci- 

 entific), HgCl2 (Reagent grade, Fisher Scientific), 

 or anhydrous CdCl2 (Reagent grade, Matheson, 

 Coleman and Bell) at concentrations of 0.1 or 1.0 

 mgAiter of the metal ion. Crabs were maintained 



in groups of 10 in 1-liter glass aquaria in 200 ml of 

 filtered seawater (30'L salinity, room temperature 

 25°C). Twice weekly the aquaria were washed out 

 and redosed. (In a similar static experimental de- 

 sign, Jackim et al. (1970) determined that the loss 

 of metal ion from solution over a 96-h period was 

 0% for cadmium, 26% for mercury, and 79% for 

 lead.) Crabs were fed twice weekly with Purina 

 Fly Chow^ In all experiments, groups were ar- 

 ranged to have the same mean carapace width and 

 to have equivalent distribution of males and 

 females (5/5). 



The growth of limb buds was measured twice 

 weekly under a dissecting microscope with a cali- 

 brated ocular micrometer. In all cases, the first 

 walking leg was measured as a representative 

 limb. Values thus obtained were converted to 

 R-values, and the means for each group were com- 

 pared by the use of the ^test. Times of molting 

 were recorded for all animals. Limb buds reached 

 R-values of about 20 just prior to ecdysis. 



Whole crabs were analyzed for mercury, cad- 

 mium, and lead following 2 wk of exposure to 0.1 

 mg/liter. Five crabs were used for each assay, 

 which was done by New Jersey Department of 

 Health personnel, using atomic absorption spec- 

 trophotometry. 



Results 



In experiment 1, crabs (mean carapace width 

 15 mm, range 13-16 mm) were exposed to 0.1 vagi 

 liter of lead, cadmium, and mercury. Ten crabs 

 were in each group, total biomass about 11 g. 

 Cadmium had a retarding effect on regeneration 

 (Table 1 ) although most individuals had molted by 

 28 days. The majority of controls molted by 21 

 days, and the rest completed ecdysis by 24 days. 

 Mercury and lead had no retarding effect. 



This experiment was repeated with crabs of a 

 somewhat smaller size (13 mm carapace width, 

 range 11-14 mm). Although cadmium again re- 

 tarded regeneration, the retardation was less and 

 was not always statistically significant (Table 1). 

 These crabs reached ecdysis at the same time as 

 controls (21 days). No effects of lead or mercury 

 were seen. 



In experiment 2, crabs were exposed to lead, 

 mercury, and cadmium at concentrations of 1.0 

 mg/liter. Carapace width of crabs was 15 mm 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



464 



