SMYTH: CALLINECTES LARVAE IN MIDDLE ATLANTIC BIGHT 



Portunus (Bookhout and Costlow 1974; Kurata 

 1975) and Callinectes (Costlow and Bookhout 

 1959; Bookhout and Costlow 1977) was present for 

 all Callinectes and most, but not all, Portunus 

 specimens. 



The profile of abdominal somites was a more 

 subjective, yet reliable, criterion for the separa- 

 tion of Portunus and Callinectes megalopae. In 

 Portunus the dorsal surface of each somite, par- 

 ticularly the first, was noticeably raised, creating 

 a "bumpy" profile; in Callinectes the profile was 

 noticeably smoother (Figure 2). (See also Book- 

 hout and Costlow 1974, fig. 11; 1977, fig. 11.) Al- 

 though identifications were based on numerous 

 characters, this particular criterion was consis- 

 tent and reliable. 



Carapace lengths in = 418, X = 1.56, SE = 

 0.004 mm) of Callinectes megalopae (measured 

 dorsally from the base of the rostrum to the pos- 

 terior edge of the carapace) were slightly less than 

 carapace lengths reported for C. sapidus (X = 1.65 

 mm) but considerably greater than lengths re- 

 ported for laboratory-reared C. similis (X = 1.30 

 mm) (Bookhout and Costlow 1977). 



I recognized no specific differences among Cal- 

 linectes megalopae or zoeae; therefore, larvae re- 

 ferred to as Callinectes may represent more than 

 one species. Abundance and known distribution of 

 adults (Williams 1974) indicated that most, if not 

 all, specimens were C. sapidus. Several small 

 adult C. similis, however, were taken in neuston 

 collections at station Cl in late October 1975. 



The above characteristics used to separate Cal- 

 linectes and Portunus megalopae were confirmed 

 by specimens reared to the juvenile stage. Por- 

 tunus juveniles were too small ( <10 mm carapace 

 width) for specific identification. One Callinectes 

 megalopa developed to a juvenile stage tentatively 

 identified as C sapidus. 



Distribution 



Callinectes larvae were collected on six of eight 

 cruises and were most abundant in late summer 

 (Figure 3). 



Mean abundance in neuston collections (n = 8) 

 at a single station reached 3,100/100 m^ at L2 in 

 August 1977; at this station abundance in a single 

 neuston collection reached a peak of 16,000/100 

 m^. Abundance generally decreased offshore of the 

 50 m isobath during the summer-fall cruises (sta- 

 tion Jl in August 1977 was an exception). During 

 the second year, with additional stations, larvae 

 were generally more abundant at stations on the 

 most southern transect than at more northerly 

 stations. Peak abundance often coincided with de- 

 pressed LSI's inshore, evidence that reproductive 

 activity inshore closely preceded the sampling 

 periods. Except during the summer, larval popula- 

 tions consisted almost exclusively of late zoeae 

 and megalopae, particularly in central and outer 

 shelf waters. Collections of Callinectes during the 

 fall of 1975 and winter and spring of 1977 com- 

 prised only megalopae. 



Mean and maximum abundance (Figure 3; 

 Table 3) was greater in neuston than in bongo 

 collections except at three stations during summer 

 1977 (Figure 3). During winter 1977, occurrences 

 were too few to be tested at the 0.05 confidence 

 level by the signed rank test. On all other cruises 

 during which Callinectes larvae occurred, abun- 

 dance was significantly greater in surface than 

 subsurface collections (Table 3). 



Diel patterns in neuston abundance of Cal- 

 linectes were not consistent over all cruises (Fig- 

 ure 4). A dawn peak in abundance was evident in 

 summer 1976. Dusk peaks appeared in fall 1975 

 and possibly spring 1977. Total abundance was 

 greatest during darkness (between sunset and 



Table 3. — Comparison of surface and subsurface (neuston vs. bongo) abundance of Callinectes larvae, based on the signed rank test 

 (Wilcoxon 1945). N denotes greater abundance in neuston, significance level indicated by asterisks (* = 0.05, ** = 0.01); P is the 

 probability of a rank sum equal or greater under the null hypothesis of equal surface and subsurface abundance; fraction in 

 parentheses: numerator is the number of occurrences in particular abundance category and denominator is the number of possible 

 occurrences in abundance category. 



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