FISHERY BULLETIN: VOL. 86, NO. 3 



snails on Monday, 10 on Wednesday, and 4 on Satur- 

 day; therefore Tuesday was assigned 15 snails, 

 Thursday and Friday 10 snails, and the total for the 

 week was 64 snail-days. 



Except where noted in the text, results were 

 analyzed by multiple analysis of covariance 

 (MANCOVA) using ranked data followed by Dun- 

 can's multiple range tests (a = 0.05) to locate sig- 

 nificant differences within the MANCOVA. Mantle 

 cavity volume was used as the covariate for com- 

 paring levels of P. marinus infection intensity, dry 

 weight, and shell weight gain between treatment 

 groups (e.g., parasitized and control oysters). 

 Similar tests comparing biochemical parameters 

 between treatment groups included the intensity of 

 P. marinus infection and tissue dry weight as co- 

 variates. When the requirement of parallelism was 

 not met, the MANCOVA was modified as described 

 by Smith and Coull (1987). Perkinsus marinus in- 

 fection intensity was used as both a dependent and 

 independent variable because, although B. impressa 

 can influence the intensity of P. marinus infection 

 (White et al. 1987), P. marinus itself can affect the 

 biochemical composition of oysters (Soniat and 

 Koenig 1982; White et al. in press). Only parasitized 

 oysters (or those recovering from parasitism) were 

 used in analyses of the effect of snail scale (intensity 

 of parasitism). 



The FAA pool was analyzed three ways: 1) the 

 entire pool, 2) the pool minus taurine and hypo- 

 taurine because these are the only amino acids not 

 found in protein, and 3) after exclusion of the major 

 components (taurine, hypotaurine, glycine, and ala- 

 nine) so that changes in the lesser constituents of 

 the pool could be examined. 



All analyses for the 4-wk exposure period used 

 MANCOVA analyses with nested variables, which 

 took into account which of the 4 domes the oysters 

 were in during the exposure period. Overall, signif- 



icant differences in biochemical composition (i.e., 

 amino acid content, glycogen, protein, etc.) between 

 the 2 nonparasitized domes or between the 2 snail 

 parasitized domes did not occur more frequently 

 than expected by chance (Binomial Test, a = 0.05). 

 Therefore, the two equivalently treated domes of 

 each treatment group (Fig. 1) were lumped together 

 for comparison with precontrol and recovery 

 oysters. Nevertheless, the experimental design 

 represents a case of pseudoreplication; hence the 

 caveats of Hurlbert (1984) should be considered 

 when reviewing the statistical analysis. 



RESULTS 



Growth, Perkinsus marinus Intensity, 

 and Reproduction 



Boonea impressa affected oyster growth rate, the 

 intensity of infection by P. marinus, and reproduc- 

 tive state. The mean initial shell weights of the 

 precontrol, control, and parasitized groups were not 

 significantly different from each other. By the end 

 of the 4-wk exposure period, both parasitized and 

 unparasitized oysters had gained weight, but oysters 

 parasitized by B. impressa gained significantly 

 less weight than unparasitized oysters (Table 1). 

 Oysters with more snails typically gained less weight 

 than oysters with fewer snails. The relationship 

 between the intensity of B. impressa parasitism 

 (snail scale) and weight gain among parasitized 

 oysters was significant (Spearman's rank, P = 0.03; 

 weight gain normalized to initial weight, P = 0.001, 

 Fig. 2). 



Mantle cavity volume did not vary among any of 

 the treatment or recovery groups. Condition index 

 was not significantly different between treatment 

 groups or between recovery groups. Condition in- 

 dex was significantly higher in the two recovery 



Table 1 .—Mean and standard deviations for initial shell weight (g) and average shell weight gain per oyster during 

 the 4-wk exposure period and 4-wk recovery period. Significance levels (sig.) from Duncan's multiple range test 

 (o = 0.05). A test was restricted to a single column. Groups having the same letter within a column are not significantly 

 different. 



556 



