Questions about source regions for recruitment of young at the beginning of the growing season, when few adults are present, are important for biological oceanographers who seek to understand what regulates the rates and geographic distributions of secondary production in the ocean. Molecular evidence was used to identify potential source regions for recruitment of C. finmarchicus onto Georges Bank. The study was particularly interesting (and particularly amenable to genetic analysis) since there may be multiple source regions, based on circulation patterns and copepod overwintering patterns, including: the Gulf of Maine [ Meise-Munns et al., 1990; Batchelder and Miller, 1991], the Slope Water [ Miller et al., 1991], the Scotian Shelf [ Sameoto and Herman, 1990 (but see Tremblay and Sinclair [1992]), and the Gulf of St.\ Lawrence [ Herman et al., 1991; Plourde and Runge, 1993]. The importance of the estuary of the St. Lawrence River for recruitment of C. finmarchicus has been emphasized by Plourde and Runge [1993], who have dubbed it a Calanus ``pump.''
or C. finmarchicus in this domain, there were moderate levels of
molecular diversity [ Bucklin et al., 1992, 1994]. The numerous,
genetically
similar haplotypes (i.e., sequence variants for a 350 base pair region of the
mitochondrial 16S rRNA) resulted in a nucleotide diversity, 
, of 0.0061
and a haplotype diversity, h, of 0.67. There were 30 different haplotypes
among 104 individuals; the haplotype frequency distribution was highly skewed,
with a single ubiquitous haplotype and numerous unique haplotypes (Figure 1).
Despite significant differences in haplotype frequencies among the samples
(
), the sample-to-sample variation (genetic ``patchiness'') of C.
finmarchicus did not resolve into regional differentiation between the Gulf of
St. Lawrence, the Gulf of Maine, and Georges Bank (
) (Figure 2),
based on chi-square tests using Monte Carlo simulations [ Roff and
Bentzen, 1989]. Comparison of the haplotype frequencies in pooled samples
of the western North Atlantic versus those in samples of C. finmarchicus
from the Norwegian Sea indicated significant genetic structure at ocean-basin
scales (
). Gene flow was relatively low across the Atlantic
(
and 
). Since gene flow is
sufficiently high to effectively homogenize the populations along the
continental shelf of the western North Atlantic, both the Gulf of St.\
Lawrence and the Gulf of Maine may function as source regions for populations
of C. finmarchicus on Georges Bank. Studies are ongoing to confirm the
importance of the Gulf of St. Lawrence as a source region and to identify
additional molecular markers that may elucidate patterns of transport within the
region.