We examined the early life stage process of the kelp Ecklonia cava from zoospore settlement to juvenile sporophyte in the field. The microspatial genetic structure of an E. cava population in a 4 m × 4 m area was analyzed using microsatellite markers to evaluate the spatial distribution of individuals. Within this area, 169 adults and 87 juveniles were analyzed, and the distributional pattern was aggregated for juveniles, uniform for adults, and random for all individuals. The kinship coefficient decreased with increasing distance and reached zero at approximately 2 m. Using a parentage analysis, the parents of 8 and 46 juveniles in the study area were identified at the 95% and 80% confidence levels, respectively. Among the juveniles, selfing was confirmed in 3 and 7 individuals at the 95% and 80% confidence levels, respectively. Although the selfing juveniles that survived appeared to grow normally, the frequent occurrence of selfing may drive the distributional change between juveniles and adults. Most of the parents had two or fewer juvenile offspring within 2.5 m in the study area. Although the stipe length of the parents did not affect the dispersal distance of the zoospores, each parent appeared to release zoospores in a specific direction. In E. cava, the local population may be maintained by the short dispersal distance of most spores and the occurrence of selfing, and the rare zoospore settlement in distant areas may allow low levels of gene flow among local populations.
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