intestinal contents, indicating that feeding was not inhibited, 

 and food was not limited. However, even though feeding was 

 taking place, this did not necessarily mean that the ingested 

 food was assimilated. The generally poor condition and 

 significantly lower frequency of crystalline styles in the 500MW 

 and WLISc mussel populations appeared to support this assertion 

 (Table 14) . 



Examinations of the effect of parasitism on gonadal 

 development revealed that in light infections, the development of 

 gametic- follicles was inhibited, while in severe cases, the 

 mussels were totally castrated. Such parasite-induced castration 

 was observed in only 34 of the 409 slides examined, constituting 

 approximately 8%; moreover, 35% of the observed castrations were 

 seen in the Rlr population. Also, the infection among the four 

 populations was not significantly different (Table 16) . Thus, 

 parasitism probably exerted only a limited stress on the mussels 

 at the three experimental stations, WLISc, 500MW, and WLISrN. 



In addition to the infection caused by Proctoeces maculatus, 

 Chytridiopsis mytilovum infection in the transplanted populations 

 was significantly higher (65-80%) than that of the Rlr population 

 (52%) (G H =3.837, d.f.=3, p<0„05). Because C^. mytilovum invades 

 ova of M^. edulis , this observation provides additional support 

 for the assertion that gonadal development in the WLISrN and 

 WLISc populations was retarded; this was reflected in the higher 

 proportion of immature individuals at these locations. 



The prevalence of Pinnotheres maculatus infection in the 

 transplanted populations was 15% less than that of the Rlr 

 population. Once a female crab enters a mussel host, it is 

 generally "imprisoned" for life due to its large size, which 

 prevents its escape. The reduction in occurrence of this 

 infection could only be explained by the death of the female 

 crabs in situ . This finding suggests that P^ maculatus is more 

 susceptible or sensitive to the changing environment at WLIS than 

 the other two parasites. However, the reduction of percent 

 infections could also be interpreted as a lack of new parasite 

 invasions into the mussel host. 



Leucocytic infiltration, a well known indicator of tissue 

 inflammation which has been used by mammalian pathologists in 

 identifying foci of abnormal tissues was of limited use in the 

 present study. Unlike that in mammalian hosts, leucocytic 

 infiltration in marine bivalve mollusks is associated with the 

 normal resorption of unspawned gametes. It is, therefore, a part 

 of the normal function of the molluscan leucocytes. Furthermore, 

 they also play an important role in nutrition and defense (Feng 

 et al. , 1977). In the present study, some of the heightened 

 leucocytic infiltration could be attributed to the presence of 

 Proctoeces maculatus and to the post spawning resorption of 



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