Jae Min Baek

Artificial seed production and cultivation of the edible brown alga, Sargassum fulvellum (Turner) C. Agardh: Developing a new species for seaweed cultivation in Korea

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.

The occurrence of pinhole disease in relation to developmental stage in cultivated Undaria pinnatifida (Harvey) Suringar (Phaeophyta) in Korea

Infection rates of pinhole disease in farmed Undaria pinnatifida (Harvey) Suringar were examined between November 2002 and April 2003 at an Undaria farm at Wando on the southwestern coast of Korea. The growth stages of U. pinnatifida can be defined as: a growth phase from December to the end of February, and a decay phase from March to April. There was a significant increase in the level of infection with pinhole disease (measured as the number of pinholes per cm2) between December and April (P < 0.01). Infection progressed from the upper part of the frond in December to the basal part in April. The infection rate of pinhole disease in relation to growth phase on farms over time is limited by the harvest of the seaweed crop at the end of the cultivation period in April. The midrib, sporophyll and stipe showed no signs of infection at any time during the cultivation period. The reduced physiological activity and tissue aging that occurred over time in the sporophytic life phase is the probable cause of the increasing infection rate of the disease.

Effects of pH and Salinity on the Cultivated Brown Alga Sargassumfulvellum and Associated Animals

The effects pH and salinity on the brown alga Sargassum fulvellum were investigated in the context of the removal of two major associated animals, Caprella scaura and Gammaropsis utinomi. Optimum quantum yield (Fv/Fm) of S. fulvellum was also examined in the same experimental conditions as an index of stress. Experiments on pH and salinity tolerances of the two animal species indicated that mortality was more than 80% at extremes of pH (2, 3, 4, 10, 11, 12) and salinity (0, 3.5, 7, 10, 44 psu) after a 5 min treatment. Lethal time (LT50) from pH 2 to pH 4 was less than 90 sec in C. scaura, and less than 70 sec in G. utinomi. From 0 to 10 psu, LT50 was less than 20 sec in C. scaura and less than 60 sec in G. utinomi. The quantum yield of S. fulvellum was not significantly different from controls within the pH range 4~10, and within the salinity range of 7-40 psu. When exposed to pH and salinity conditions outside these ranges, the effect of these factors on the removal of two animal species was higher, but quantum yield was highly reduced. These results indicate that the optimal conditions for removing the animal species without affecting optimum quantum yield were pH 4-10, and salinities 7-10 psu and 44 psu.