Maturation Rates of the First-year Sporophyte of an Early Maturing Perennial Kelp Ecklonia cava

Abstract

The sporophytes of the warm temperate perennial kelp Ecklonia cava are known to mature from the second year. In some populations, however, thalli were recently suggested to mature within one year of germination in field observations, but the precocity was not directly confirmed in culture studies. In the present study, maturation rate of first-year sporophytes was examined for the first time. Free-living gametophytes were obtained from two wild populations in Moroiso and Jogashima Island, Miura Peninsula. The sporophytes derived from these populations were reared in a land-based tank (Exp. 1) or in open sea conditions (Exp. 2), respectively. The maturation rates of the sporophytes in the first year were 66% in Exp. 1 and 60% in Exp. 2. At the time of the maturation check, both stem diameter and total length were significantly larger in mature thalli than in immature ones (p<0.01, except total length in Exp. 1). Since the precocious thalli can mature earlier than the peak of browsing by herbivorous fishes (summer to autumn), they can be considered as candidates of a donor of zoospores to produce seedlings for restoration and expansion of the kelp beds.