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.

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.