Jung Rok Lee’s research while affiliated with Wonkwang University and other places

The red alga Chondria crassicaulis has a wide‐ranging bioactive chemical composition and is used as a local foodstuff, representing a potentially new cultivar in Korea. The cultivation techniques were developed by examining the monthly changes in frond weight in a field population of C. crassicaulis from November 2016 to October 2017. For seedling production, temperature and irradiance effects on the attachment and growth of vegetative propagules of C. crassicaulis were evaluated. In addition, effects of day length and salinity on the propagule growth were examined. C. crassicaulis is a year‐round species with a maximum frond wet weight of 817 mg observed in July 2017, as seawater temperature increases to 20°C. The attachment of vegetative propagules was significantly affected by temperature and irradiance, with maximal values detected at 20–25°C and 60 µmol photons m−2 s−1. The relative growth rates of vegetative propagules of C. crassicaulis were the highest at 20–25°C, 60 µmol pho‐ tons m−2 s−1, and a salinity of 25 psu. In conclusion, due to its tremendous tolerance under variable environmental conditions, the vegetative propagules of C. crassicaulis can be used as seedlings for mass cultivation.

Sediment loading by human activities has increased in recent years and sedimentation in coastal areas is problematic because it removes seaweed forests. In this study, we examined the effects of different sediment quantities (0, 2, 4, and 6 mg cm −2) and particles sizes (<100, 100-250, and 250-600 μm) on zygote attachment, and germling survival and growth of Sargassum thunbergii, an economically and ecologically important species. Zygote attachment was negatively correlated with increased sediment quantities. However, it was not significantly different among sediment particle sizes. In addition, survival and growth of germlings were significantly inhibited by increased sediment quantity. Smaller particle size (< 100 μm) had greater negative impact on the survival and growth than bigger ones. Results of the present study suggest that early development of S. thunbergii is significantly inhibited by sediment. This might be a vital factor that results in forest depletion in Korea.

Silvetia siliquosa is an ecologically and commercially important brown alga that is harvested from its natural habitats, but its population has recently been diminishing along the Korean coast. To develop new techniques for algal population restoration, we tested two newly developed transplantation methods (using polyethylene ropes and natural rock pieces) at two study sites, Gwanmaedo and Yeongsando, on the southwest coast of Korea, from May to November 2014. The transplants on polyethylene ropes showed significantly greater survival, maturity, and growth than those on natural rocks at both study sites. Newly recruited juveniles (<3 cm) of S. siliquosa increased remarkably from May to December near the transplants on polyethylene ropes and natural rocks. Therefore, we suggest that transplantation using polyethylene ropes is more effective than using natural rocks to restore the population of S. siliquosa in Korea.

We examined the effects of environmental factors on zoospore release and germling growth of the green tide alga Cladophora albida under various conditions of temperature{\times}irradiance (zoospore release), temperature{\times}irradiance{\times} nutrient (germling growth), and a single factor test of salinity. Zoospore release was maximized at 30^{\circ}C and 100µmol\;photons\;m^{-2}s^{-1} in the temperature irradiance experiment and at 34 psu in the salinity experiment. Maximum germling growth was observed at 25^{\circ}C with 100µmol\;photons\;m^{-2}s^{-1} and PES (Provasoli`s Enriched Seawater) in the temperature irradiance nutrient experiment, and at 34 psu in the salinity experiment. Germlings grew faster at higher irradiances for a given temperature level, and also grew faster as salinity increased over the range of 5-34 psu. Overall, optimal environmental conditions for zoospore release were 30^{\circ}C, 100µmol\;photons\;m^{-2}s^{-1} and 34 psu. Maximal germling growth occurred at 25^{\circ}C, 100µmol\;photons\;m^{-2}s^{-1}, PES, and 34 psu. C. albida blooms are most likely to occur under these optimal environmental conditions, as plentiful zoospore release and rapid germling growth lead to population growth.

Seasonal variations in seaweed communities were examined at Gwanmaedo and Yeongsando, Korea, from May 2014 to February 2015. Eighty-nine species were identified, including 11 green, 20 brown and 58 red algae. Seventy-three and 74 species were identified at Gwanmaedo and at Yeongsando, respectively. Sargassum thunbergii and Myelophycus simplex were the dominant species, comprising 60.89 and 39.50% of total biomass, respectively, and S. fusiforme was subdominant at the two sites. Of six functional seaweed forms, the coarsely-branched form was the most dominant, forming about 43% of the species number at Gwanmaedo and Yeongsando. Seasonal seaweed biomasses ranged between 53.10 and 172.85 g/m? (average 93.57 g dry wt./m?) and between 83.11 and 176.20 g (138.21 g/m?) at Gwanmaedo and Yeongsando, respectively. The vertical distribution from the high to low intertidal zone was S. thunbergii and Gloiopeltis furcata; M. simplex and S. thunbergii; and S. fusiforme at Gwanmaedo. Seaweed zonation was distinct at Yeongsando, with S. thunbergii and Gelidiophycus freshwateri; M. simplex and S. thunbergii; and S. thunbergii and S. fusiforme. Seaweed biomass, evenness index (J'), and diversity index (H') values were greater at Yeongsando (138.21 g/m?, 0.51, 2.18 respectively) than at Gwanmaedo (93.57 g/m?, 0.48, 2.04), indicating that the seaweed community at Yeongsando is more stable than that at Gwanmaedo.

Seaweeds were identified after qualitative sampling at 14 stations of Dokdo coasts from May to July 2013 and seaweeds and animals inhabiting 23 Eisenia bicyclis plants were examined to evaluate its ecological role. Biomass was calculated by using regression between stipe length and weight of E. bicyclis. A total of 128 species were identified, including 18 green, 35 brown, and 75 red algae. Coarsely branched form was dominant functional group occupying 47.66% and 91 species (71.09%) were in ESG I group, growing in stable environmental coast. Also, R/P, C/P, and (R+C)/P were 2.14, 0.51, and 2.66, respectively showing temperate and mixed flora. Biomass and density of E.bicyclis were 23.74kg m-2 and 64 fronds m-2. Twelve seaweeds and 83 animal species (15 Annelida, 25 Mollusca, 34 Arthropoda, 3 Echinodermata, and 6 others) were observed from 23 holdfasts and Ericthonius pugnax was dominant taxon having 538 (43.11%) of 1,248 animal individuals. These results indicate that E.bicyclis is a keystone species showing very important ecological role. In conclusion, the number of seaweeds increased because of intensive research and dominance of coarsely branched form and ESG I group seaweeds, representing that environmental condition of Dokdo is still intact.