SMYTH: CALLINECTES LARVAE IN MIDDLE ATLANTIC BIGHT 



Table 2. — Station data forzooplankton collections in the Middle 

 Atlantic Bight, 1975-77. 



larval densities. Tows were of 20-min duration 

 except when large abundances of neuston required 

 premature termination of a tow. The net was me- 

 tered beginning with the June 1976 cruise; before 

 that cruise, sample volumes were estimated on the 

 basis of a standard 20-min tow. Tows were made 

 from an extended boom alongside the ship at 

 speeds of 1.5-2.5 kn. 



During the second year two stations to the north 

 and a transect to the south of the original transect 

 were added. On each cruise neuston samples were 

 taken over 24 h at nine stations (Figure 1; Table 2: 

 A2, B5, CI, E3, Jl, LI, L2, L4, L6). A single neus- 

 ton tow was made at stations Dl, N3, and F2 as a 

 companion to bongo tows. Bongo tows were made 

 at all 12 stations following the procedure used 

 during the first year. In addition, replicate tows 

 were made at stations A2, B5, and E3 (repeated 

 tows of two bongo nets with paired 202 yum and 

 505 yum mesh nets). Three such replicate tows 

 were made at night at each designated station. 



Samples were preserved in a 4% solution of 

 borax-buffered formaldehyde and seawater 

 (Steedman 1976). In the laboratory, major 

 taxonomic groups were quantitatively sorted from 

 whole or split samples (Burrell et al. 1974). Deca- 

 pods were sorted to species and identified (when 

 possible ) on the basis of published descriptions and 

 taxonomic keys. 



Megalopae of several taxa, including Cal- 

 linectes , were reared aboard ship to juveniles. Sev- 

 eral megalopae were removed from a sample and 

 tentatively identified or identification characters 

 noted. Megalopae were placed in plastic tackle 

 boxes with 505 ixm mesh bottoms and the boxes 

 were floated in an aquarium filled with seawater 

 taken in situ. Megalopae were fed Artemia salina 

 nauplii and bits of fresh fish meat. Megalopae with 

 the same characteristics as the megalopae used for 

 rearing were fixed and preserved. 



Abundance was expressed as number per 100 

 m^; for graphical presentation and certain statis- 

 tical procedures abundance was compressed by the 

 transformation logio(Z + 1). Most statistical pro- 

 cedures were based on station means, with eight 

 neuston collections per station. The distribution of 

 sample means tends to normality as the sample 

 size increases (Snedecor and Cochran 1967), and 

 the logarithmic transformation tends to make var- 

 iance independent of the mean (Sokal and Rohlf 

 1969). Based on the i^-max test (Sokal and Rohlf 

 1969), untransformed abundances within stations 

 were very heteroscedastic, while log-transformed 

 abundances at stations with Callinectes larvae in 

 at least six samples did not have unequal var- 

 iances at P <0.05. Coefficients of variation for each 

 station were reduced considerably by the log 

 transformation, and abundances appeared better 

 centered about the median based on "box and 

 whisker" diagrams (Tukey 1977). The assumption 

 of a multivariate normal distribution could not be 

 tested for the data set. Significance levels for 

 mulitvariate data are often difficult to interpret; 

 therefore, significance levels, where indicated for 

 parametric procedures, should be taken as a guide. 



A larval stage index (LSI) similar to that of 

 Manzi and Maddox ( 1976) was calculated for sev- 

 eral larval types. The LSI is a point along the 

 continuum of development from hatching (first 

 zoea) to juvenile; the LSI characterizes the stage of 

 an average individual of a given species in a sam- 

 ple. It is calculated as a weighted average, i.e., 



LSI = 



2 iSi 



f=i 



where i 

 n 



number of the developmental stage, 

 number of developmental stages, 

 first zoeae through adult, 

 abundance of the ith stage. 



The LSI is standardized and constrained in the 

 interval 0.0-1.0 by the assignment of a stage 

 number (1> the megalopa) to the adult stage. 

 Thus, an LSI = 0.67 characterizes animals that 

 have completed, on the average, about two-thirds 

 of the developmental sequence from hatching to 

 first crab. The LSI is, however, a measure of cen- 

 tral tendency and does not indicate statistical dis- 



253 



