Abstract

Sargassum fusiforme is a commercially important macroalga in Eastern Asia. To support the conservation and restoration of S. fusiforme populations, we investigated its predominant reproductive mode using a population genetics approach. Two sampling schemes were employed: random sampling of 80 samples at > 1 m intervals across four sites, and quadrat sampling of 207 samples using 50 cm × 50 cm quadrats subdivided into 10 cm grids at two sites. Clonemates were identified based on the microsatellite genotypes. In random sampling, only three clonal pairs were detected. In the quadrat sampling, each quadrat contained 4–7 genets, with an average extent of 23.2 ± 14.3 cm (standard deviation) and a maximum of 70.7 cm. The genetic indices (Pareto β, inbreeding coefficient, variance of inbreeding coefficient, genotypic richness, and synthetic linkage disequilibrium) suggested higher clonality at Site B than at Site D. Contemporary gene flow analysis indicated that over 65% of sexual recruitment was limited to within the quadrats, whereas at least 10% extended over meters to kilometers. Taken together, these results suggest that S. fusiforme disperses its offspring both sexually and clonally on a small scale and sexually on a larger scale.

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