Shields et al.: Fecundity and reproductive potential of Cancer anthonyi 



301 



Results 



General observations 



Ovigerous females varied from 89 to 153 mm in cara- 

 pace width (Fig. 1), with a mode at 140 mm. Broods of 

 C. anthonyi were oviposited without observed prior 

 mating or molting by the female crab, and were ob- 

 served for every mature crab held in the laboratory; 

 some crabs brooded at least three clutches per year in 

 the laboratory (Table 1). At a mean seawater tempera- 

 ture of 15°C, crab eggs took approximately 40 days 

 to develop from oviposition to eclosion (Table 1). Subse- 

 quent broods were typically produced within 1-2 months 

 after eclosion of the previous brood. Crab embryos 

 from subsequent broods (second and third) were viable 

 and hatched normally. In addition, the seminal recepta- 

 cles of 24 crabs that were dissected after the eclosion of 

 at least a second brood contained viable spermatozoa. 



Broods oviposited in sand- and gravel-bottomed 

 aquaria were smaller than those from crabs in the field 

 (mean fecundity/pleopod = 2.75 ± 0.73(SD) x 10 5 , ver- 

 sus 4.10 ± 0.67 (SD) x 10 5 ; N = 12 and 12, respective- 

 ly; t = 4.72, P< 0.001); but food or holding effects may 

 have confounded ovarian develop- 

 ment and fecundity in lab-held crabs. 



Cancer anthonyi brooded an esti- 

 mated 0.73-3.30 million eggs per 

 clutch depending on crab size. Crab 

 fecundity (log fecundity/pleopod) 

 was significantly different between 

 broods in different stages of em- 

 bryogenesis (Table 2; ANOVA, 

 Sidak's inequality, F<0.05). Clutch 

 size did not differ significantly be- 

 tween broods in early and middle 

 stages of development, hence these 

 broods were combined for the size- 

 fecundity analyses. 



At eclosion, female crabs active- 

 ly aided the hatching process. Fe- 

 males stood upon all of their legs 

 and vigorously aerated their brood 

 by agitating their abdomens and 

 pleopods. Water currents through 

 the gill chamber appeared to reverse 

 their usual direction and flowed 

 anteriorly through the egg mass. 

 This facilitated eclosion, and pushed 

 hatched prezoeae out of and away 

 from the clutch. Within 2-3 days 

 after hatching, female crabs stripped 

 their pleopods of empty and dead 

 eggs. The setae of cleaned pleopods 

 attained a golden sheen comparable 



Table 2 



Changes in log fecundity/pleopod with embryogenesis. EDS 

 refers to developmental stages of embryogenesis [class 1, EDS 

 I-II; class 2, EDS III-IV; class 3, EDS V-VII; class 4, EDS 

 VIII] (Shields and Kuris 1988a, Shields et al. 1990). Days of 

 development are based on temperatures of 15°C. Values with 

 different letters are significantly different (ANOVA, Sidak's 

 inequality, P<0.05). 



EDS 

 class 



Days of 

 development 



N 



Fecundity/pleopod 

 (log no. of eggs) ± SD 



1-12 

 13-30 

 31-38 

 39-40 



97 



129 



78 



31 



5.504 ± 0.200 

 5.517 ±0.201 

 5.399 ± 0.239 

 4.748 + 0.421 



to their appearance on a freshly molted crab. 



Size-fecundity relationship 



The fecundity per pleopod (log) was positively corre- 

 lated with crab size (log CW) (R 0.521, P<0.001, 

 N 219; Fig. 2), but fecundity per crab (log) was not 



2.00 



2.08 2.12 



Carapace width (log mm) 



2.16 



Figure 2 



Size (CW)-fecundity relationships for Cancer anthonyi with broods in different stages 

 of embryogenesis. Fecundities of crabs with eggs in early and middle stages of em- 

 bryogenesis (boxes, solid line) and late embryogenesis (diamonds, dashed line) were 

 highly correlated with crab size (in early and middle EDS, log fecundity/pleopod = 

 2.135(log CW) + 1.015, R = 0.521, N = 219; in late EDS, log fecundity/pleopod = 

 3.321(log CW) + 1.637, R = 0.544, N = 70; P<0.001 for both). Fecundities of crabs 

 with eggs near hatching (triangles, dotted line) were not correlated with size (log 

 fecundity/pleopod = 0.723 (log CW) + 3.217, R = 0.055, N = 30, P>0.05). See text for 

 ANCOVA results. 



