Donax clams are an abundant species on
the beaches of North Carolina and reports suggest the occurrence of multiple
species. This study uses both morphometric and genetic analysis of specimens
collected from four different locations at three different depths to clarify
the species composition and distribution on Wrightsville Beach, North Carolina.
A total of 12 clams were collected by benthic coring at three depths at each of
four sites. Abundance differed significantly between sites with over 50% of the
clams being collected from a single site. Clams were more abundant in the swash
zone relative to the subtidal depths (knee and waist deep water) . Using the
diagnostic characteristics of shell angle and the relationship between shell
width and shell length, morphometric analysis supported the finding that there
is only one species present on Wrightsville Beach. The angle measurement had a
calculated mean of 129.3° which was very close to reported values for Donax
variabilis. Regression analysis of shell width length and height
relationships also suggested the presence of a single species. Genetic analysis
of the mitochondrial 16s gene revealed a small level of nucleotide diversity.
Twenty-three samples were sequenced and 415 base pairs compared. Three sites were
polymorphic and one site exhibited an insertion/deletion. Comparison of the 23
sequences revealed the presence of four haplotypes. Nucleotide sequence
diversity was estimated to be well within the range reported for populations of
a single species. The results of these analyses suggest the presence of a
single species on Wrightsville Beach, NC.