HAWKES ET AL.: RHIZOCEPHALAN PARASITISM OF ALASKA KING CRAB 



was inhibited considerably more than in parasitized 

 male L. aequispina. The condition factor for non- 

 parasitized male L. aequispina (6.5 ± 0.5) was also 

 greater at a highly significant level than for male 

 parasitized crabs (6.1 ± 0.4). The condition factor 

 in parasitized and nonparasitized male golden king 

 crabs did not vary significantly with size 



Nonparasitized female L. aequispina (n = 77) were 

 heavier than parasitized females (n = 43) over most 

 of the length range The linear relationships were 

 significantly different but not parallel, preventing 

 a comparison of the intercepts. Condition factors 

 were not significantly different between the 

 parasitized (5.9 + 0.5) and nonparasitized (5.7 + 0.4) 

 females. Condition factors varied significantly with 

 size and in the nonparasitized crabs but not in the 

 parasitized crabs. 



DISCUSSION 



Weights and, consequently, condition factors were 

 significantly lower in male blue and golden king 

 crabs parasitized by B. callosus. A difference in mean 

 weight was also present in female blue king crabs 

 that were parasitized, although an adequate com- 

 parable sample size of nonparasitized females was 

 not available The prevalence of the parasite was con- 

 siderably greater in king crab populations where sub- 

 legal or smaller size classes of adult crabs were in- 

 cluded in the sample number. In blue king crabs from 

 Glacier Bay, the inclusion of females in the sample 

 also raised prevalence figures since females had a 

 significantly higher prevalence of barnacle para- 

 sitism than male crabs. A potential reason for in- 

 creased barnacle prevalence in smaller crabs could 

 include differential mortality such that fewer 

 parasitized crabs survive to larger size classes. Other 

 explanations include reduced molting frequencies, 

 reduced number of instars and/or reduced growth 

 represented by a reduction in relative molt increment 

 (Hawkes et al. in press). However, reduced weights 

 in parasitized crabs within the same size classes as 

 nonparasitized individuals suggest that growth of the 

 host crab is decreased by B. callosus. The higher 

 parasite prevalence in smaller crabs also supports 

 this conclusion. 



Parasitized crabs may develop significantly less 

 body tissue after molting, which is likely to be a 

 cumulative effect occurring over more than one 

 season. Although the complete life history of B. 

 callosus is unknown, other species of Rhizocephala 

 are known to require at least 9 to 12 mo to reach 

 reproductive maturity and develop an externa in host 

 crabs (Ritchie and H0eg 1981). In males that be- 



come castrated and weight loss of testes is insignif- 

 icant in total body mass (0.2%) and does not account 

 for the weight difference observed. Also testes weigh 

 less than the interna and externa of the parasite In 

 female king crabs a considerable amount of the wet 

 body weight can be attributed to the egg clutch and 

 ovaries. Consequently, gonadal atrophy, nonovigerous 

 conditions and reduced somatic growth rates all may 

 account for the lesser weights observed in parasi- 

 tized female king crabs. 



The percentages of weight difference between 

 parasitized and nonparasitized males was con- 

 siderably different between the two species of king 

 crabs. Golden king crab was less affected by the 

 parasite, sustaining less growth inhibition due to bar- 

 nacle parasitism than parasitized blue king crabs. 

 Parasitized golden king crabs have significantly 

 higher hemolymph protein concentrations in com- 

 parison to either their nonparasitized conspecifics 

 or parasitized blue king crabs. The additional pro- 

 tein may be attributed to the presence of lectins, 

 specific carbohydrate-binding proteins suspected of 

 playing a role in crustacean immunity (Shirley et al. 

 1985). 



If we are correct, reduced crab growth as an ef- 

 fect of B. callosus parasitism would conflict with data 

 from other peltogastrid rhizocephalans (O'Brien and 

 Van Wyk 1985). Other rhizocephalan species tend 

 to be more prevalent on larger crab hosts, making 

 enhanced growth or enhanced survivorship a plaus- 

 ible effect of parasitism. Another explanation is that 

 parasitized crabs have less somatic growth and, as 

 a result, have fewer molts. Molting is a time of 

 greatest mortality for most decapods, and those with 

 lower molting frequencies would have greater sur- 

 vival. The probability of infection may also be greater 

 in certain size classes. Behavioral differences or 

 sampling bias could affect the parasite's relative fre- 

 quency within the host population. Sacculinidae ap- 

 pear to be distributed differently within host popula- 

 tions (O'Brien and Van Wyk 1985). Pugettia producta 

 is a majid crab from California and does not molt 

 after reaching maturity. When parasitized by the 

 rhizocephalan Heterosaccus californicus, there is no 

 significant effect on molt increments of juveniles and 

 the pubertal molt increment is not affected in adults. 

 However, P. producta that are parasitized pass 

 through fewer instars before reaching maturity, and 

 the mean size of these individuals is significantly less 

 than in nonparasitized crabs (O'Brien 1984). Blue 

 crabs, Callinectes sapidus, also have retarded growth 

 when parasitized by Loxothylacus texanus, with most 

 adults appearing as miniature adult females (Over- 

 street 1978). 



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