. The Biological bulletin. Biology; Zoology; Marine biology. NEMERTEAN NUMBERS AND DEVELOPMENT 135 worms than small ones, but they also have more area to harbor worms and from results of the analysis of variance tests, it appears that worms are not selecting crabs on the basis of size. From data on the per cent of infected crabs, the average number of worms/ crab, and the analysis of variance results, it can be seen that in both species females with eggs are most heavily infected, followed by males, then by females without eggs. There was a strong seasonal component to both the infection rate
. The Biological bulletin. Biology; Zoology; Marine biology. NEMERTEAN NUMBERS AND DEVELOPMENT 135 worms than small ones, but they also have more area to harbor worms and from results of the analysis of variance tests, it appears that worms are not selecting crabs on the basis of size. From data on the per cent of infected crabs, the average number of worms/ crab, and the analysis of variance results, it can be seen that in both species females with eggs are most heavily infected, followed by males, then by females without eggs. There was a strong seasonal component to both the infection rate and the number of worms per crab in both populations of crabs (Figs. 1, 2) and in all groups of crabs. The worm population was highest from October to January with sharp peaks in November. The peaks in worm population precede the winter reproductive period of H. oregonensis (Fig. 1) which is the major reproductive period for this crab species (Kuris, 1978; Roe, personal observation). The fall peak in the worm population does not correspond at all to the (summer) repro- ductive cycle of P. crassipcs (Fig. 2) ; indeed, most of the infection of this species is also in fall and winter (Fig. 2) even though females brooding eggs are the most heavily infected hosts when they are present. Average number of worms /crab Percentoqe of crabs with worms Percentage of female crobs brooding eggs. July A S 0 N 1975 Feb A M J J AS 1976 TIME Figure 2. Percentage of Pachygrapsus crassipcs population at Elkhorn Slough, Cali- fornia, harboring Carcinoncmcrtcs epialti externally, average number of worms/crab, and per- centage of females of the crab population that were brooding eggs each month. Vertical lines along the solid line are one standard error from the mean and are shown only when the standard error exceeded For most months, sample size was 25 crabs (July 1975, N = 14; August 1975, N = 18; September and October 1975, N = 20; November 1975, N = 24; July 1976, N = 22; October 1976, N = 2
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