GENETIC-VARIABILITY AND SPATIAL SEPARATION IN THE SEA PALM KELP POSTELSIA-PALMAEFORMIS (PHAEOPHYCEAE) AS ASSESSED WITH M13 FINGERPRINTS ANDRAPDS

Postelsia palmaeformis Ruprecht is an annual species, occuring from so uthern California to Vancouver Island Canada, in upper intertidal site s exposed to extreme wave shock. Because of its limited spore dispersa l, discrete and inbred populations are likely on the local scale, yet dispersal of drifting and fertile thalli raises the possibility of out bred populations on a regional scale. M13 minisatellite DNA fingerprin ting and random amplified polymorphic DNA (RAPD) markers were used in a complementary fashion to investigate genetic variability among 24 in dividuals on scales of clusters (= coalesced holdfasts). <1 m, 20 m, 2 5 m, 16 km, and 250 km. Based on M13 fingerprinting, genetic relatedne ss within clusters was extremely high. Three of six clusters had at le ase two identical individuals, and similarity values within five clust ers were greater than or equal to 0.90. Similarities between. two of t hree clusters separated by <1 m were significantly higher than between cluster pairs separated by 25 m and 250 Km: however, the similarity b etween two clusters separated by 25 m was equivalent to the similarity between two clusters separated by 250 km. Thus, genetic relatedness a s determined by M13 fingerprinting generally decreased as distance inc reased to 25 m. Conversely, RAPD data easily discriminated populations separated by 16 and 250 Km but were not useful in discriminating indi viduals from <1 to 25 m. Results from the complementary data sets sugg est that most dispersal occurs over distances of 1-5 m, individuals wi thin a cluster are siblings, and distinguishable biogeographic populat ions are present along the coast.