Morphological and DNA sequence variation in the kelp Costaria costata (Phaeophyta)

Kelp species show substantial intraspecific morphological variation. The annual kelp, Costaria costata (C. Agardh) Saunders, is found in the lower intertidal and subtidal regions of shores which vary in exposure from strongly wave-exposed to sheltered. Phenotypic variation was studied in this monotypic genus. Individuals of C. costata were collected from two morphologically-distinct populations (one wave-exposed and the other wave-sheltered) at Cape Beale and Stanley Park, Vancouver, Canada, in May 1985. Analysis of morphological variation, using multivariate statistical techniques, indicated significant differentiation between plants from the two sites. Blade widths and thicknesses were the major discriminating variables. Restriction fragment length polymorphism (RFLP) analysis of nuclear DNA with 42 anonymous probes demonstrated one polymorphism. Most of the probes are hypothesized to encode highly repeated, dispersed sequences. These repeat sequence probes comprised 80.9% of all cloned fragments. Primary sequence analysis of 1595 base pairs of small-subunit ribosomal DNA and 204 base pairs of upstream sequence (probe pCc 18) failed to show any divergence between plants from the two sites.