Early development of Costaria costata (C. Agardh) Saunders and cultivation trials

Costaria costata (C. Agardh) Saunders is one of common kelps distributed in many coastal areas worldwide; however, in China, no reports have been made on cultivation of the genus. To investigate potential cultivation of the species in the northern part of China, trials on isolation and preservation of the gametophytes were conducted using C. costata from Korea; growth and development of the gametophytes were observed. We showed that at 10±1°C, 60 μmol m⁻²s⁻¹ and 12:12 h (L:D), freshly released zoospores settled down within 1 hour, and then developed into the primary cell during the following 2 days. After a vegetative growth phase lasting 6–8 days, female gametophytes became 3–4 times larger in diameter than that of the primary cell, but still remained at a unicellular stage, while male gametophytes divided into 4–10 cells with only a slight change in size. Fertilization occurred within 10 days after the zoospores were released from the sporangia, and the apical and basal tissues of the juvenile sporophyte divided and differentiated into the blade and stipe. Temperature and irradiance influenced gametophytic vegetative growth and developmental patterns. Generally, low irradiance (15 μmol m⁻²s⁻¹ and 30 μmol m⁻²s⁻¹) was unfavorable to the induction of fertility, but it enhanced female gametophyte division. The optimal conditions for vegetative growth were 15°C and 30 μmol m⁻²s⁻¹. After transplantation of the juvenile seedlings and after eight months cultivation, the harvested mature blade reached 194 cm in length and 32.7 cm in width. Our study proves that it is feasible to implement propagation and large scale cultivation of C. costata in northern China.