• Ocean and Polar Research
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• v.27 no.2
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• pp.125-133
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• 2005

This study described the phonology and reproductive potential of four species of Korean seagrasses, Zostera caespitosa, Z. caulescem, Z. Japonica and Z. marina. Z. caespitosa and Z. caulescens sampled from a mixed stand at the subtidal area of Yulpo Bay, Geojedo of the South Sea of Korea in November 2002 and August 2003. Z japonica and Z. marina occurred at the depth between the middle intertidal and shallow subtidal (<1m below mean sea level) of Seungbongdo (in Yellow Sea) samples collected in February and October 2003. The sexual reproductive phase of the four Zostera species was apparently different in timing of flowering, reproductive period, fruiting and seed maturing. Z. caespitosa flowered from February to early May $(10-16^{\circ}C)$, and its seed production completed in early May. The reproductive shoots of Z. caulescens began to appear in January $(9^{\circ}C)$, and its flowering followed from February to June $(10-19^{\circ}C)$. The flowers of Z. japonica were observed from July to September $(18-22^{\circ}C)$, and its seeds matured from August to September. The most commonly I marina flowered from April to August $(7-21^{\circ}C)$ and developed into seeds in July. Z. caulescens, the largest plant, had the highest number of seeds per shoot and longest spadix length. Z. marina, which was intermediate In size, recorded the highest reproductive potential. The study indicates that the reproductive phase and potential of the four species of seagrass from Korea are highly related to water temperature, and the populations of these species show a perennial lifespan with a low sexual reproductive input.

• Korean Journal of Environmental Biology
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• v.35 no.4
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• pp.492-500
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• 2017

The purpose of this study was to investigate the seasonal distribution of phytoplankton as prey for oysters and to characterize the environmental factors controlling their abundance from June 2016 to May 2017, in the northeast coast between Tongyeong and Saryang Island, particularly for the oyster farming area. During the survey period, water temperature changed from $7.54^{\circ}C$ in February to $29.5^{\circ}C$ in August. The abnormal high temperature persisted during one month in August. Salinity was low due to summer rainfall and typhoon. The lowest level was 30.68 psu in September, and it peaked at 34.24 psu in May. The dissolved oxygen (DO) concentration ranged from $6.0-9.45mg\;L^{-1}$, and the DO concentration in the surface layer was like that in the bottom layers. The seasonal trends of pH were also like those of DO. The pH ranged from 7.91 to 8.50. Nitrate with nitrite, phosphate, and silicate concentrations ranged from $0.14{\mu}M$ to $7.66{\mu}M$, from $0.01{\mu}M$ to $4.16{\mu}M$, and from $0.27{\mu}M$ to $20.33{\mu}M$, respectively. The concentration of chlorophyll a (Chl. a) ranged from $0.37{\mu}g\;L^{-1}$ to $2.44{\mu}g\;L^{-1}$ in the surface layer. The annual average concentration was $1.26{\mu}g\;L^{-1}$. The annual mean phytoplankton community comprised Bacillariophyta (69%), Dinophyta (17%), and Cryptophyta (10%), respectively. Dinoflagellate Prorocentrum donghaiense in June was the most dominant at 90%. In the summer, diatom Chaetoceros decipiens, Rhizosolenia setigera and Pseudo-nitzschia delicatissima were dominant. These species shifted to diatom Chaetoceros spp. and Crytophyta species in autumn. In the winter, high densities of Skeletonema spp. and Eucampia zodiacus were maintained. Therefore, the researchers thought that the annual mean Chl. a concentration was relatively lower to sustain oyster feeding, implying that the prey organism (i.e., phytoplankton) was greatly controlled by continuous filter feeding behavior of oyster in the vicinity area of the oyster culture farm.

• ALGAE
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• v.32 no.2
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• pp.101-130
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• 2017

The ichthyotoxic Cochlodinium polykrikoides red tides have caused great economic losses in the aquaculture industry in the waters of Korea and other countries. Predicting outbreak of C. polykrikoides red tides 1-2 weeks in advance is a critical step in minimizing losses. In the South Sea of Korea, large C. polykrikoides red tide patches have often been recorded offshore and transported to nearshore waters. To explore the processes of offshore C. polykrikoides red tides, temporal variations in 3-dimensional (3-D) distributions of red tide organisms and environmental parameters were investigated by analyzing 4,432 water samples collected from 2-5 depths of 60 stations in the South Sea, Korea 16 times from May to Nov, 2014. In the study area, the vegetative cells of C. polykrikoides were found as early as May 7, but C. polykrikoides red tide patches were observed from Aug 21 until Oct 9. Cochlodinium red tides occurred in both inner and outer stations. Prior to the occurrence of large C. polykrikoides red tides, the phototrophic dinoflagellates Prorocentrum donghaiense (Jun 12 to Jul 11), Ceratium furca (Jul 11 to Aug 21), and Alexandrium fraterculus (Aug 21) formed red tides in sequence, and diatom red tides formed 2-3 times without a certain distinct pattern. The temperature for the optimal growth of these four red tide dinoflagellates is known to be similar. Thus, the sequence of the maximum growth rates of P. donghaiense > C. furca > A. fraterculus > C. polykrikoides may be partially responsible for this sequence of red tides in the inner stations following high nutrients input in the surface waters because of heavy rains. Furthermore, Cochlodinium red tides formed and persisted at the outer stations when $NO_3$ concentrations of the surface waters were < $2{\mu}M$ and thermocline depths were >20 m with the retreat of deep cold waters, and the abundance of the competing red-tide species was relatively low. The sequence of the maximum swimming speeds and thus potential reachable depths of C. polykrikoides > A. fraterculus > C. furca > P. donghaiense may be responsible for the large C. polykrikoides red tides after the small blooms of the other dinoflagellates. Thus, C. polykrikoides is likely to outgrow over the competitors at the outer stations by descending to depths >20 m and taking nutrients up from deep cold waters. Thus, to predict the process of Cochlodinium red tides in the study area, temporal variations in 3-D distributions of red tide organisms and environmental parameters showing major nutrient sources, formation and depth of thermoclines, intrusion and retreat of deep cold waters, and the abundance of competing red tide species should be well understood.

• Korean Journal of Poultry Science
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• v.28 no.3
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• pp.215-224
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• 2001

Since nitrogen(N) is a volatile compound affected by many environmental factors, determining the N content of manure tends to be difficult. Upon arrival in the laboratory, the manure should be moist and refrigerated. Manure samples will have variable N contents due to drying temperature, and the presence of soil in the sample will affect N content. Acidification of the sample prevents ammonia volatilization and should be done before drying. It is recommended that manure samples be pretreated with a strong oxidizing agent, KMnO$_4$, followed by digestion under reduced conditions (reduced Fe-$H_{2}$ $SO_{4}$ ), which achieves a complete recovery of both $NO_{3}$ -N and $NO_{2}$ -N without a low recovery of $NH_{4}$ -N, resulting in a more accurate determination of N content. Accuracy of results for N content determined by recently developed rapid analysis techniques in the field should be tested by comparison with results obtained at laboratories using approved standard methods. Most commonly, the Kjeldahl system is used to determine manure N content. More research is needed on the effects of species, breed, age and individuals on the nutrient contents of manure. The procedures for manure sampling on the farm, shipping and handling of the sample until it reaches the laboratory, and the methods of sampling of the manure at the laboratory must be studied. Development of animal agricultural laboratories where feed, manure, soil, and water are all analyzed by appropriate specialists is needed.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.26 no.2
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• pp.182-197
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• 1993

Algal community on the subtidal rocky zone of the South Sea of Korea was divided into two or three sequencing zones. The upper subtidal zone was characterized by the wave exposure-tolerant surf wrack(Pachymeniopsis, Gigartina), which formed dense swirling carpet. Its vertical range was from the surface to $3{\sim}5$ meters in depth, and more deeply extended in turbid waters including Sorido, Yokchido, Pijindo, Manjedo. The mid subtidal zone ranging from 5 to 25 meters in depth was characterized by a large brown algal forest (Ecklenia, Sargassum). But it was generally unrecognizable in that turbid waters, in which the vertical limit of vegetation was at most $10{\sim}15$ meters in depth. The low subtidal zone was characterized by a general lack of algal species and was not easily distinguished from the mid or sometimes from the upper zone. There was a distinct difference in abundance of vegetation between turbid waters and clear waters including Munsom, Kwantaldo, Yosodo, Hongdo, Ch'ujado. In turbid waters the vegetation was much poorer because the tubidity caused from the muddy sediment inhibited an algae to settle down and to grow up. On the basis of the phytogeographical methods using UPGMA, the 10 studied islands were classified into two groups, Munsom and the others. This floristic discontinuity between the two groups might be caused from the difference of water temperature.

• Ocean and Polar Research
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• v.27 no.2
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• pp.149-159
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• 2005

Samples were collected from five stations in February, May, July, and September 2004 to investigate seasonal variations in the phytoplankton community and the relationship between dominant genera and environmental factors in Asan Bay. In February, microphytoplankton contributed 80% to the total chlorophyll a. Diatom dominated the phytoplankton community, accounting for 85.9% of the total cell number, followed by dinoflagellates (6%). Dominant species were Skeletonema costatum and Thalassiosira spp. Abundant diatom, including S. costatum and Thalassiosira spp., may be affected by water temperature and silicate at Station 1 and 2 in February 2004. In May, the nanophytoplankton contribution to total phytoplankton was higher than in other seasons. However, abundance of S. costatum and Thalassiosira spp. decreased, since the growth of S. costatum and Thalassiosira spp. might be limited by phosphates (P) resulting from low P concentration and a high DIN:DIP ratio in the outer region. In July, dominant phytoplankton groups were diatom (39%), cryptophyceae (28%), and cyanophyceae (20%). Dominant genera were Oscillatoria spp. and phytoflagellate of a monad type in the inner region (Station 1 and 2), whereas S. costatum was dominant in the outer region (Station 4 and 5). In September, dominant phytoplankton were diatom (69%) and cryptophyceae (28%). Dominant genera were phytoflagellate of the monad type, S. costatum in the inner region, while Chaetoceros spp. was dominant in the outer region.

• The Korean Journal of Malacology
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• v.19 no.2
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• pp.143-152
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• 2003

Water temperature during the culturing period was 10.4-25.5$^{\circ}C$ and there was a little difference between rearing sites. Salinity (25.00-31.17 psu) and DO (over 6.13 mg/l) showed reasonable condition for the growth of bay scallop. Concentrations of chlorophyll-a were ranged 1.69-7.40 $^{\mu}$g/l, and they fluctuated monthly in the every sampling site. During the growing period from June to October, dominant phytoplankton species were Ceratium sp. in Nammeon and Hoejin, Chaetoceros sp. in Dolsan. Density of phytoplankton was high in July, August and October, but it was low in September and November. When young bay scallops were cultured for 185 days in Nammyeon, Hoejin and Dolsan, shell heights were grown for 0.19 mm/day, 0.18 mm/day and 0.16 mm/day, respectively, and total weights were increased 0.16 g/day, 0.16 g/day and 0.13 g/day, respectively. Daily growth rates of shell height were 0.606%, 0.581% and 0.549%, and daily growth rates of total weight were 1.972%, 1.857% and 1.746%, respectively. Maximum predicted values of shell height calculated by von Bertalanffy growth model were 52.62 mm, 51.74 mm and 48.91 mm, respectively. Survival rate was the highest in Nammyeon (87.0%), but the rates in Hoejin and Dolsan sharply decreased after November.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.5
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• pp.707-712
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• 1998

Seasonal variation in the proximate composition, cholesterol (CHOL) and $\alpha$-tocopherol ($\alpha$-Toc) content of 12 spices of fish muscle, which caught off Tongyeong coast of the Southern Sea (Nam-Hae) from Mar. 1995 to Feb. 1996, was studied. Lipid and moisture content showed remarkable seasonal variation and there were a negative correlation between the both (r= -0,85, p<0.001), while protein and ash content unchanged almost through the sampling period. The lipid content of anchovy, hickoryshad, black sea bream, finespotted flounder sea eel, bastard, and file fish was high in Dec. Oct. Nov. Jan. Jan. Nov, respectively, and low in the season corresponding to their spawning period. However, in case of striped mullet, yellow tail, mackerel, rock fish and red sea bream, there was no correlation between their lipid content and spawning period, and thus these fishes fore considered to be affected more by water temperature and the content of their diet. CHOL content increased In :he season containing a high level of lipid, whereas $\alpha$-Toc content unchanged almost through the sampling period.

• Korean Journal of Agricultural Science
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• v.28 no.1
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• pp.18-26
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• 2001

Application of the Asian ladybird (Harmonia axyridis) to control several species of aphids in the plastic green houses in mind, control effects of aphid populations regulated by the Asian ladybird were observed. The green peach aphid, the turnip aphid, and the cotton aphid were present on mustard plants, Angelia utlis, ornamental kales, and egg plants at greenhouses in spring, summer, and winter. Adults and larvae of the Asian ladybird used in experiments were collected from aggregated sites at Taejon in the autumn and reared on the cotton aphid in the laboratory. In winter, more number of adults and larvae of ladybirds than in other seasons were needed to control aphid population in successively double plastic greenhouses with supplied subterranean water for keeping warmth. In spring and summer, it was possible to keep the aphid populations low when necessary by manipulating ladybird populations according to the density of aphids. On the other hand, the innate increasing rate of aphid, the aphid population density at the time of applying ladybird, the predacious ability of ladybird at specific developmental stages, and needed periods should be taken into account to control aphids. In addition, the environmental factors, for example, optimum temperature and humidity should be considered to be biologically effective when ladybirds are released to greenhouses.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.6
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• pp.669-676
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• 2017

To understand the relationship between environmental factors and phytoplankton community structures and why early outbreaks of Cochlodinium polykrikoides occur in the inner bay of Korea, short-term investigations were conducted at 17 stations in the eastern part of the South Sea of Korea, with sessions every two weeks from July 7 to August 24, 2016. The water temperature increased from $22.3^{\circ}C$ in the first survey to $28.4^{\circ}C$ in the fourth survey, which was a rise of about $6.01^{\circ}C$. Salinity was relatively high at Stns. 8 13 in the inner bay. In the first survey, rainfall of about 150 mm was observed, so nutrients were supplied at a high level and a high concentrate of Chl. a was observed. Cryptophyta (Crpytomonas spp.) represented 58.3 % of the community, followed by Bacillariophyta at 33.8 %. In particular, at Stn. 5, Dinophyta Prorocentrum spp. accounted for a very high percentage, 32.2 %. In the second survey, low phytoplankton populations were observed, and Bacillariophyta (Chaetoceros spp.) accounted for 61.0 %. At Stn. 4, Skeletonema spp. showed high populations but did not appear at other stations even at a low density. In the third and fourth surveys, phytoplankton populations were very low. Bacillariophyta represented 78.0 % in the third study and 73.3 % in the fourth. Interestingly, although the appearance of C. polykrikoides was investigated at the beginning of the red tide in the coastal area, they were not observed inshore, implying that the likelihood of inflow by the germination of resting cysts was low for the inner bay during this study period. In addition, environmental characteristics such as salinity and nutrient presence were significantly different between sampling stations due to the existence of a semi-closed bay in the southern sea, resulting in dominant phytoplankton species and community composition differing in these short-term investigations.