• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.3
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• pp.226-236
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• 1999

Growth, reproduction, mortality, and production of Laminaria japonica were experimentally studied at a cultivation ground on the coast of llkwang, where the largest amount of cultivated Laminaria has been produced in Korea. For this experiment, young sporophytes (0.33 cm in mean length) grown in the laboratory were transplanted at the depth of 3 m and field surveys on them were conducted twice a month from December, 1995 to August, 1996. Plants exhibited an annual life span; they were completely dead by August. Frond width, thickness, and wet weight showed similar pattern of seasonal growth and reached their maxima in July, but frond length showed no more increment after May. Maximum mean frond length and weight were 199.8 cm and 333.0 g wet wt., respectively. Overall meristematic growth in length and weight were 384.0 cm and 393.6 g wet wt., respectively. Absolute growth rates (AGR) which were calculated from the length of tissue developed from meristem varied seasonally; AGR of length and weight reached maxima in March (3.6 $cm{\cdot}d^{-1}$) and May (3.8 g wet $wt{\cdot}d^{-1}$), respectively. Absolute attrition rates gradually increased from February to July. Seasonal differences in growth and attrition rates appeared to be related to seawater temperature and nitrogen concentration in seawater. Reproductive sporophytes bearing sprorangium sorus began to occur from April, and the ratio of sorus area to blade area reached its maximum in July (0.034). Survival rate was exponentially decreased; more than 90% of plants decayed within 56 days after outplanting. After February, mortality was size-specific; mortality of smaller plants less than 30 cm in length were relatively higher. Maximum biomass occured in July (285.6 kg wet $wt{\cdot}m^{-2}$) and annual production was 758.7 kg wet $wt{\cdot}m^{-2}$.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.32 no.4
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• pp.438-443
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• 1999

Germination and growth of Laminaria japonica microscopic stages were investigated under crossed gradients of temperatures and irradiances, and the results related to the seasonal temperature regime in the southeastern coast of Korea. Germination rates of $70\~86\%$ were observed in the temperature range of $5\~20^{\circ}C$, however, at $25^{\circ}C$ no germination of meiospores was observed. The primary factor affecting germination rates at the temperature range of $5\~20^{\circ}C$ was irradiance: germination was significantly reduced at $150 {\mu}E{\cdot}m^{-2}{\cdot}s^{-1}$. Vegetative cell production of female gametophytes was highest at $20^{\circ}C$, but plants were not fertile at the temperature. In the temperature range of $5\~15^{\circ}C$, higher irradiance caused females to reduce cell production, but increased fertility. Cell production was also low at lower temperatures with increased fertility rates. Optimal growth temperature for microsporophytes was $10^{\circ}C$ and their growth rates were light-saturated at $70 {\mu}E{\cdot}m^{-2}{\cdot}s^{-1}$. We have concluded that meiospores released before July could develope to the young sporophytic stage in the southeastern coast of Korea which is off the southern limit of its geographical distribution. However, limiting factor in the development of natural sporophytic population in this region would be the upper temperature limit for the survival of young sporophytes, as water temperature at this area frequently exceeds $25^{\circ}C$ during the summer period.

• Korean Journal of Environmental Biology
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• v.17 no.1
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• pp.1-9
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• 1999

Numerous observations revealed strong evidence of increased middle ultraviolet radiation or UV-B (280 ~ 320 nm) at the earth's surface resulting from stratospheric ozone depletion. UV is the waveband of electromagnetic radiation which is strongly absorbed by nucleic acids and proteins, thus causing damage to living systems. It has been recorded in the East Sea, Korea that solar UV-B impinging on the ocean surface penetrates seawater to significant depths. Recent researches showed that exposure to UV-B for as short as 2h at the ambient level (2.0 Wm$^{-2}$) decreased macroalgal growth and photosynthesis and destroyed photosynthetic pigments. These may suggest that UV-B could be an important environmental factor to determine algal survival and distribution. Some adaptive mechanisms to protect macroalgae from UV-damage have been found, which include photoreactivation and formation of UV-absorbing pigments. Post-illumination of visible light mitigated UV-induced damage in laminarian young sporophytes with blue the most effective waveband. The existence of UV-B absorbing pigments has been recognized in the green alga, Ulva pertusa and the red alga, Pachymeniopsis sp., which is likely to exert protective function for photosynthetic pigments inside the thalli from UV-damage. Further studies are however needed to confirm that these mechanisms are of general occurrence in seaweeds. Macroalgae together with phytoplankton are the primary producers to incorporate about 100 Gt of carbons per year, and provide half of the total biomass on the earth. UV-driven reduction in macroalgal biomass, if any, would therefore cause deleterious effects on marine ecosystem. The ultimate impacts of increasing UV-B flux due to ozone destruction are still unknown, but the impression from UV studies made so far seems to highlight the importance of setting up long-term monitoring system for us to be able to predict and detect the onset of large -scale deterioration in aquatic ecosystem.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.32 no.4
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• pp.444-451
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• 1999

The effect of individual density on the growth and survival of Laminaria japonica was experimentally evaluated. Four density treatments of young sporophytes (0.63 cm In maximum length) grown in the laboratory were transplanted to the southeastern coast of Korea and their survivorship and growth rate were measured twice a month from January to July, 1996. Plants showed higher survivorship at low density. Final densities at three lowest densities were similar, ranging from 34 to 38 inds${\cdot}100 cm^{-2}$. Planis at the highest density, however, suffered greater decline than at lower densities, and only 21 plants remained at the end of this study. Mean frond size (length and width) fluctuated throughout the study period at four densities. During the first two mouths after outplanting, mean frond size was negatively correlated with initial density, However, the size was density independent after three months. As stand density increased, size-frequency distribution through time tended to be more positively skewed. The 10 largest plants grew faster in frond size and attained larger size in the lower density. There was a positive relationship between plant size and relative growth rate (or survival). The slope of yield-density (Y-D) relationships at four densities ranged from -0.060 to -0.137. The study suggests that density can strongly affect the survival and growth of this alga. The density-dependent survival and growth patterns, however, were not strictly consistent with those of terrestrial plants.