Seaweed aquaculture technologies have developed dramatically over the past 70 years mostly in Asia and more recently in Americas and Europe. However, there are still many challenges to overcome with respect to the science and to social acceptability. The challenges include the development of strains with thermo-tolerance, disease resistance, fast growth, high concentration of desired molecules, the reduction of fouling organisms and the development of more robust and cost efficient farm systems that can withstand storm events in offshore environments. It is also important to note that seaweed aquaculture provides ecosystem services, which improve conditions of the coastal waters for the benefit of other living organisms and the environment. The ecosystem services role of seaweed aquaculture and its economic value will also be quantitatively estimated in this review.

The use of seaweeds as human food in eastern Asian countries has a long history, stretching back over a thousand years. However, it was not until the late 1940s that cultivation of seaweeds in near-shore coastal areas began. Due to their location, the Korean peninsula, the Japanese islands and the Chinese coasts share a similar seaweed flora in their coastal waters, and it is not surprising that seaweed species chosen for cultivation, methods of farming and post-harvest processing in these countries have a lot in common. In 2016, the total seaweed production in these three countries reached 16,218,406 t, approximately 53.8% of global seaweed production (FAO). In the course of seaweed farming development in eastern Asia, the development and use of seaweed cultivars have contributed significantly to the seaweed farming industry in terms of improving both the biomass yield and the quality of the food products produced. In this article, the recent development of cultivar-related research and applications practised in Korea, Japan and China are reviewed with particular reference to the key commercial species: Saccharina japonica, Pyropia spp., Undaria spp., Cladosiphon okamurarus, and Nemacystus decipiens. In the past 21 years, 47 certified seaweed cultivars have been used in commercial cultivation in these countries. While much of the development effort has focused on increasing yields, a current emphasis in cultivar breeding programs is to increase the quality of farmed seaweed products. More recently, molecular analyses have been integrated into these programs and have become indispensable tools in the breeding process.

The occurrence of encrusting colonies of the hydroid Obelia geniculata on farmed Saccharina japonica was examined between

Tribute to This paper is dedicated to the memory of Professor Chul Hyun Sohn (1943~2019) Mariculture is regarded as the only option to supply the increasing demands for seaweeds as human food, feeds, fodder, and phycolloids in a sustainable manner. Technologies for culturing a range of seaweed species have been developed successively in Korea since the 1970s. In 2017, Korean marine farms produced 1,761,526 t of seaweed. The key focus of the industry is on the production of Pyropia (523,648 t), Undaria (622,613 t), and Saccharina (542,285 t). Pyropia is economically the most important species in Korea, accounting for up to 68% of total production value. As the top exporter of Pyropia in the world, Korea exported up to US $525 million of Pyropia products to 110 countries in 2018. Other economically important genera include Sargassum, Ulva, Capsosiphon, Codium, and Gracilariopsis, all of which are used for food, and Gelidium, Pachymeniopsis, and Ecklonia which are used as raw material for phycocolloid extraction. Significant work has gone into developing more productive strains of key seaweed species, and in 2012 the Korean government began to certify seaweed varieties. To date, 19 seaweed cultivars have been registered including 13 Pyropia, 5 Undaria, and 1 Saccharina. The industry is now seeking not only to increase productivity but also to add value through processing. Convenience foods and snacks have been developed that target health-conscious consumers and utilize the nutritional properties of seaweeds. The industry is also seeking to promote the sustainability of seaweed farming. One seaweed company in Korea obtained the world's first ASC-MSC (Aquaculture Stewardship Council-Marine Stewardship Council) certification in 2019 and more are expected to follow their lead. With continued research support, the Korean seaweed industry plans to continue to expand to meet new market demands at a sustainable pace.

The mass cultivation of Ecklonia stolonifera Okamura was studied as a possible summer feed for the abalone industry in Korea for the period between August and November when Undaria and Laminaria are not available. Experiments were conducted to investigate the optimal conditions for artificial seed production and mass cultivation of this species. Seedlings of E. stolonifera were reared in an indoor tank for 60 days until they were around 500 μm in length. Following indoor tank culture, the seedlings were transferred in situ to a nursery culture area for 2 months, before begin transferred to the main grow-out area. The maximum growth and development of young thalli in nursery culture area occurred at 2 m depth, whilst maximum growth of thalli in the main culture area occured at 1.5 m depth. Production of E. stolonifera was between 3 and 9 kg wet wt. m −1 in the first year of culture after seeding and 12 to 13 kg wet wt. m −1 in the second year of culture, after management (depth control and fouling organism removal, etc.) of the holdfast. The relationship between optimal water depth for culture and underwater irradiance during the E. stolonifera cultivation was defined as: y =−0.331x+ 8.198 (r 2 =0.9903). The growth rates achieved in this trial indicate that E. stolonifera cultures could produce sufficient biomass to supply summer feed for the Korean abalone industry.

In this study, we investigated the effect and mechanism of Undariopsis peterseniana, an edible brown alga, on hair growth. The treatment of vibrissa follicles with U. peterseniana extract ex vivo for 21 days significantly increased the hair-fiber lengths. The U. peterseniana extract also significantly accelerated anagen initiation in vivo. Moreover, we found that U. peterseniana extract was able to open the KATP channel, which may contribute to increased hair growth. The U. peterseniana extract decreased 5α-reductase activity and markedly increased the proliferation of dermal papilla cells, a central regulator of the hair cycle. The U. peterseniana extract increased the levels of cell cycle proteins, such as Cyclin D1, phospho(ser780)-pRB, Cyclin E, phospho-CDK2, and CDK2. The U. peterseniana extract also increased the phosphorylation of ERK and the levels of Wnt/β-catenin signaling proteins such as glycogen synthase kinase-3β (GSK-3β) and β-catenin. These results suggested that the U. peterseniana extract had the potential to influence hair growth by dermal papilla cells proliferation through the activation of the Wnt/β-catenin and ERK pathways. We isolated a principal of the U. peterseniana extract, which was subsequently identified as apo-9′-fucoxanthinone, a trichogenic compound. The results suggested that U. peterseniana extract may have a pivotal role in the treatment of alopecia.

The kelp Undariopsis peterseniana is warmwater-tolerant, and consequently, there is currently considerable interest in developing commercial cultivation techniques for this species in Korea. U. peterseniana plants have been successfully transferred to the northern coast of Korea beyond their original habitat in Jeju Island (33°30′08.65″N, 126°55′39.02″E). In this study, we cultured a hybrid kelp consisting of a cross between free-living gametophytes of U. peterseniana and U. pinnatifida in an attempt to extend the culture period of Undaria which is an important species for both the abalone industry and for commercial seaweed mariculture for human food applications. Morphological characters and cultivation period were compared between the parent thalli and the hybrid. The cultivation experiment was conducted in Wando, on the southern coast of Korea (34°26′18.68″N, 127°05′ 43.88″E). The morphological characteristics of the hybrid thalli were intermediate between the two species having shallow pinnated blades and a reduced reproductive organ. Hybrid thalli showed faster growth rates, 1.5 times greater biomass, and a longer cultivation period than the parent thalli. The hybrid strain possessed characteristics that indicate it could be used as an alternative kelp source to supply the abalone feed industry.

Sargassum fulvellum is a brown alga recently introduced to the seaweed cultivation industry in Korea. There is current interest in the commercial scale of aquaculture of this species. For the artificial seeding and cultivation of this alga, growth and maturation were investigated from September 2002 to August 2003. Indoor culture experiments for maturation induction were also conducted at temperatures of 5, 10, 15, 20 and 25 • C and irradiances of 20, 50, 80 and 100 μmol photons m −2 s −1 under 16:8 h (L:D) photoperiod. Within a given culture test range, higher temperature and irradiance levels favoured the maturation of receptacles in S. fulvellum. Using temperature and irradiance control for thalli, artificial seed production of this species could be done one month earlier than thalli matured in nature. Under natural condition, receptacle formation of the plants began in February, and the eggs were released from March to April. For mature thalli of 200 g wet wt., artificial seeding was complete enough for attachment on seed strings of 100 m. Mean production obtained from the artificial seeding technique in situ was 3.0 kg wet wt m −1 of culture rope during the cultivation period.