The green macroalga Cladophora vadorum bloomed along the coast at Sangrok Beach, Buan, South Korea, in September 2015. To elucidate the cause of bloom, the effects of environmental factors on the vegetative growth of adult fragments were examined. Growth experiments were carried out under different combinations of temperatures and irradiances, and with a single factor of nutrients (nitrogen, phosphorus). The maximal growth of C. vadorum was reported under the combination of 25°C and 100 μmol photons m -2 s -1 . The species grew under a wide range of N and P concentrations. The growth of C. vadorum peaked at 50 μM PO 4 3-, 80 μM NH 4 + , and 100 μM NO 3 -. Adult fragments formed holdfasts and new branches within 3 days in culture and became adults, showing polarized growth patterns, in 2 weeks. This is the first report showing the development of numerous bladelets from a segment in Cladophora species. The present results indicate that Cladophora blooms appear under growth conditions that are favorable in terms of temperatures, irradiance, and nutrients via fragment growth patterns producing rapid holdfasts and many bladelets.

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 2 (average 93.57 g dry wt./m 2 ) and between 83.11 and 176.20 g (138.21 g/m 2 ) 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 2 , 0.51, 2.18 respectively) than at Gwanmaedo (93.57 g/m 2 , 0.48, 2.04), indicating that the seaweed community at Yeongsando is more stable than that at Gwanmaedo.

The effects of CO 2 concentration, nutrient levels, and irradiance on the growth of germlings and juveniles, and on the photosynthesis of adults were examined in a green tide alga, Ulva australis. We used a factorial experimental design with two CO 2 concentrations (380 and 750 ppm), two nutrient levels (control and PES medium), and two irradiance levels (50 and 100 μmol photons m -2 s -1 ). Germlings grew best (664.15±61.45 μm in length) under conditions of 750 ppm, PES, and 100 μmol photons m -2 s -1 after 10 days in culture. Relative growth rates (RGR) of the juveniles were greatest (4.41% day -1 ) under conditions of 750 ppm, PES, and 50 μmol photons m -2 s -1 after 5 days in culture. Photosynthetic efficiency (F v /F m ) of the adult discs was 0.73 ± 0.05 before the experiment and reached a maximum (0.83±0.01) under conditions of 750 ppm, control, and 50 μmol photons m -2 s -1 after 5 days in culture. Growth (germlings and juveniles) and photosynthesis (adult discs) of Ulva australis increased when CO 2 levels were 750 ppm. Additionally, the optimal irradiance for growth and photosynthesis differed among stages, wherein germlings grew best at 100 μmol photons m -2 s -1 , juveniles grew best at 50 μmol photons m -2 s -1 , and adults photosynthesized most at 50 μmol photons m -2 s -1 . The performance of Ulva australis at all examined life stages was enhanced under the PES nutrient treatment. In conclusion, the physiological responses of U. australis to varying CO 2 , nutrient, and irradiance levels differed slightly among life stages. However, growth and photosynthesis always increased with elevated CO 2 and nutrient concentrations. These results indicate that U. australis green tide blooms might occur more frequently in coastal areas if CO 2 and nutrient concentrations increase.

No abstract

We examined seasonal variation in the structure of marine macroalgal communities at five sites around the Byeonsan Peninsula, Korea, from January to October 2011. Sixty eight species were identified, including 11 green, 17 brown and 40 red algae. Species richness was highest at Gyeokpo (51 species) followed by Sambal (47), Gosapo (34), Byeonsan (33), and Habgoo (18). Seaweed biomass ranged from 12.98 to 145.33 g dry wt/m 2 , with maximum and minimum biomasses at Gyeokpo and Habgoo, respectively. Sargassum thunbergii was the representative alga species occupying 47.89% of the total biomass. The dominant seaweeds were S. thunbergii, Corallina pilulifera, Ulva spp, Gracilaria vermiculophylla, and Carpopeltis affinis. No distinctive vertical distribution of seaweeds was found because S. thunbergii, Ulva spp, and G. vermiculophylla were all distributed from high to low shore. Community indices were as follows: dominance index (DI), 0.44-0.61; richness index (R), 6.27-10.35; evenness index (J'), 0.38-0.59; and diversity index (H'), 1.48-1.71. Gyeokpo had the most biomass and highest species richness, and the lowest percentage of Ulva species. However, species richness declined at Gyeokpo, from 78 to 51 species within 10 years, implying that eutrophication and sedimentation from Mankyeong and Dongjin rivers have reduced the stability of seaweed communities.