Appearance and characteristics of major phytoplankton species based on long-term monitoring datasets in southern sea of Korea.

To understand the mechanism of phytoplankton bloom forming, we investigated the relationship between several species and water quality factors using long-term monitoring datasets from 1996 to 2003. The seven sites at this study were classified into four groups by phytoplankton species or water quality datasets and the species for phytoplankton bloom forming seems to be mainly influenced by the water quality or surrounding water conditions. E. gymnastica and P. minimum were observed for the longest time period from April to September, and C. polykrikoides shortest time period from summer to autumn. E. gymnastica was observed across the widest temperature range (14–27ºC), and C. polykrikoides narrowest temperature range (20–28ºC). Chaetoceros spp. was observed over the narrowest salinity range (22–33 ppt), and E. gymnastica, P. minimum, H. akashiwo wide salinity range (14–34 ppt). The main reasons for the formation of Chaetoceros spp. and S. costatum blooms seems to be fresh water input through forest and fields by heavy rainfall events. Thalassiosira spp. seems to grow well in conditions of fresh water input and/or in eutrophicated areas with salinities >20 ppt and water temperatures >17ºC. C. furca seems to grow well in sea areas that are affected by inflows of domestic and industrial wastewater and by inflows of freshwater with domestic and industrial wastewater, rather than only freshwater input, after May when water temperatures are higher than 18ºC. E. gymnastica, H. akashiwo, P. minimum, and P. triestinum seem to grow well in eutrophicated sea areas where nutrient levels are high and where domestic and industrial wastewater flow are abundant. C. polykrikoides blooms seem to be due to suitable seawater input from off sea areas, and freshwater after heavy rainfall that has high nitrogen concentration.

Diurnal vertical migration of Cochlodinium polykrikoides during the red tide in Korean coastal sea waters.

The diurnal vertical migration of Cochlodinium polykrikoides (C. polykrikoides), which caused a red tide in the Korean coastal waters of the East Sea/Sea of Japan in September 2003, was examined by determining the time-dependent changes in the density of living cells in relation to the depth of the water column. The ascent of this species into the surface layer (depth of water, 2 m) occurred during 1400- 1500. The descent started at 1600 and a high distribution rate (86%) at 15-20 m was observed at 0300. During the ascent, the cells were widely distributed at each depth level from 0600 hr and at 0800-1100, the cells were primarily distributed in the middle layer (0-6 m). The concentration of dissolved inorganic nitrogen was generally <2.86 μmol l -1, but at 1400-1500, the concentration in the surface layer reduced to <0.14 μmol l -1. Moreover, the concentration gradually increased as the depth increased to > 5 m. These results showed that the nutrientconsumption rate associated with the proliferation of C. polykrikoides during a red tide is more influenced by the inorganic-nitrogen resources rather than the inorganic-phosphorus compounds.

Survival and growth of Cochlodinium polykrikoides red tide after addition of yellow loess.

We examined the survival rate of Cochlodinium polykrikoides after yellow loess addition and conducted culture experiments to investigate the possibility that red tides may be caused by C. polykrikoides individuals that are precipitated when loess is added. At least 15% of the C. polykrikoides cells that precipitated to the bottom layer either by the addition of loess or no addition survived for 1 week at all growth phases, rather than disappearing immediately after precipitating. However, no live cells were observed after 20 days, regardless of phase or loess addition. In the exponential phase, the number of C. polykrikoides cells increased to >2886 cells ml-1 after loess was added. However, in the stationary phase, the number of cells did not increase until 18 days. In the exponential phase, those C. polykrikoides that survived precipitation caused by scattering loess on cultures did not appear to have the ability to cause red tides again because of the short red tide periods in the field, long lag time after loess addition, and low survival rate after loess addition.

Organic and inorganic matter increase related to eutrophication in Gamak Bay, South Korea.

Water quality, the carbon isotope ratio of suspended particulate organic matter (POM), and limiting nutrients were investigated at seven surface and bottom seawater stations in Gamak Bay, South Korea, to evaluate the effectiveness of counter-measures to organic matter increase. The increase in surface water COD in Gamak Bay appear to be the result of phytoplankton growth, which is consistently limited by nitrogen (N) or phosphorous (P), but not by silicon (Si). High chlorophyll a concentrations seem to be caused by freshwater inputs of N and P associated with wastewater in the northern and northeastern portions of the Bay, and by the inflow of NH4-N and P associated with the digestion of organic matter from the bottom layer in western areas. To regulate the increase of organic matter in Gamak Bay, controlling phytoplankton growth, particularly by regulating the input of N or P, may be more important than controlling the input of terrestrial organic matter.

Estimation of Cochlodinium polykrikoides growth potential using a dialysis membrane.

We developed a test to measure the growth potential of C. polykrikoides using a dialysis membrane and artificial seawater. Nitrite nitrogen and inorganic phosphorus in the medium were almost completely removed when the medium was dialyzed against artificial seawater for five or more 6-hour cycles using a dialysis membrane (Spectrum's Spectra/Por 7 Membrane) with a molecular-weight cut-off of 50,000, regardless of the presence of C. polykrikoides. The phytoplankton grew well even after dialysis. To estimate the growth potential of C. polykrikoides, a minimum initial concentration of > 100 cells/ml is required. Methods using short-term starvation culturing of C. polykrikoides to measure growth potential were determined to be ineffective; instead, controlled tests using artificial seawater are recommended. The dialysis membrane used in this study can also be employed to measure the algal growth potential of other phytoplankton species.

Utilization of various nitrogen, phosphorus, and selenium compounds by Cochlodinium polykrikoides.

The abilityof Cochlodinium polykrikoides to use various nitrogen, phosphorus, and selenium compounds as a nutrient source was examined in batch culture experiments to obtain biological information on the mechanism of C. polykrikoides bloom formation. C. polykrikoides grew using a variety of organic or inorganic nitrogen sources except for L-proline. Maximum yields of C. polykrikoides were obtained by gradually increasing ammonium from 5 to 20 microM, but the yield was inhibited by addition of more than 50 microM. Growth was observed in media containing various phosphorus sources, such as phosphate and 11 different organic compounds. Organic nitrogen and phosphorus seem to play an important role in the dominance of phytoplankton species and mass growth of C. polykrikoides. The ability to use a variety of organic nutrients may allow C. polykrikoides to grow to a high density in spite of inorganic nitrogen and phosphorus depletion. C. polykrikoides grew in the presence of selenite, selenate, and Se-(methyl) selenocysteine hydrochloride. However, growth yield was inhibited by addition of more than 500 microM selenate and 1000 microM Se-(methyl) selenocysteine hydrochloride. Therefore, much of the oil effluents seen in 2005 may have a temporary inhibitory action on C. polykrikoides growth but can be expected to have a positive effect in the long term.