Genetic differentiation
among western Atlantic samples was less than that either
between Gulf of Mexico and western Atlantic samples or
among Gulf of Mexico samples (Table 2). Temporal genetic
variation among samples collected from Charleston Harbor over a period of 4 years followed the overall pattern
of little differentiation, while the two collections from the
Mississippi River Delta from 1996 and 1997 were significantly
different. These two collections were from slightly
different locations (Fig. 1), so there may have been either local geographical or temporal variation. Comparisons of
allele frequency distributions of combined Gulf of Mexico
samples and combined western Atlantic samples were significantly
different after Bonferroni correction at locus Pse36,
and combined over loci,
P
< 0.01 (Table 3).