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Changes in Floating Population Distribution in Jeju Island Tourist Destinations Before and After COVID-19 Using Spatial Big Data Analysis (공간 빅데이터 분석을 활용한 COVID-19 전후 제주도 관광지의 유동인구 분포 변화)

  • Heonkyu Jeong;Yong-Bok Choi
    • Journal of the Korean Association of Geographic Information Studies
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    • v.27 no.1
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    • pp.12-28
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    • 2024
  • This study aims to identify the trend of changes in tourist floating population before and after COVID-19 in major tourist destinations in Jeju Island through spatial analysis. Seongsan-eup and Andeok-myeon in Jeju Island were selected as the research area, and the research period was set at 1 year before and 2 years after the COVID-19 outbreak. For the analysis, mobile floating population data was refined and processed to calculate floating population distribution and floating population increase/decrease data. This was converted into spatial data and an overlay analysis was performed with location data of major tourist attractions. As a result of the analysis, it was confirmed that the floating population of indoor tourist attractions and small facilities decreased immediately after COVID-19, and that in open coastal areas or large facilities, the floating population decreased less or actually increased. In conclusion, in tourism development, it is necessary to identify changes in floating population according to the characteristics of tourist facilities, and it is necessary to develop tourism facilities and strategies that can respond to risk situations such as pandemics when developing tourist destinations.

Field and laboratory investigation of highly pathogenic avian influenza H5N6 and H5N8 in Quang Ninh province, Vietnam, 2020 to 2021

  • Trong Duc Tran;Suwicha Kasemsuwan;Manakorn Sukmak;Waraphon Phimpraphai;Tippawon Prarakamawongsa;Long Thanh Pham;Tuyet Bach Hoang;Phuong Thi Nguyen;Thang Minh Nguyen;Minh Van Truong;Tuan Pham Dao;Pawin Padungtod
    • Journal of Veterinary Science
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    • v.25 no.2
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    • pp.20.1-20.15
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    • 2024
  • Background: Avian influenza (AI) is a contagious disease that causes illness and death in poultry and humans. High pathogenicity AI (HPAI) H5N6 outbreaks commonly occur in Quang Ninh province bordering China. In June 2021, the first HPAI H5N8 outbreak occurred at a Quang Ninh chicken farm. Objectives: This study examined the risk factors associated with HPAI H5N6 and H5N8 outbreaks in Quang Ninh. Methods: A retrospective case-control study was conducted in Quang Ninh from Nov 2021 to Jan 2022. The cases were households with susceptible poultry with two or more clinical signs and tested positive by real-time reverse transcription polymerase chain reaction. The controls were households in the same village as the cases but did not show clinical symptoms of the disease. Logistic regression models were constructed to assess the risk factors associated with HPAI outbreaks at the household level. Results: There were 38 cases with H5N6 clade 2.3.4.4h viruses (n = 35) and H5N8 clade 2.3.4.4b viruses (n = 3). Compared to the 112 controls, raising poultry in uncovered or partially covered ponds (odds ratio [OR], 7.52; 95% confidence interval [CI], 1.44-39.27), poultry traders visiting the farm (OR, 8.66; 95% CI, 2.7-27.69), farms with 50-2,000 birds (OR, 3.00; 95% CI, 1.06-8-51), and farms with ≥ 2,000 birds (OR, 11.35; 95% CI, 3.07-41.94) were significantly associated with HPAI outbreaks. Conclusions: Combining biosecurity measures, such as restricting visitor entry and vaccination in farms with more than 50 birds, can enhance the control and prevention of HPAI in Quang Ninh and its spread across borders.

Connectedness of the dry bulk carrier market before and after COVID-19 (COVID-19 전후의 건화물선 시장의 연계성)

  • Jung, Dae-Sung;Choi, Ki-Hong
    • Journal of Korea Port Economic Association
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    • v.40 no.2
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    • pp.157-173
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    • 2024
  • This study analyzed the connectivity of the dry bulk carrier market before and after COVID-19 to examine the impact of COVID-19 on the global shipping market. Using the Quantile Time Frequency Connectedness methodology, we analyzed the dynamic connectedness of major dry bulk indices: the Capesize Index (BCI), Supramax Index (BSI), Panamax Index (BPI), and Handysize Index (BHSI). The results are as follows. First, the total spillover connectedness of the dry bulk carrier market increased during the entire period and in the short term after the outbreak of COVID-19, while it slightly decreased in the long term. Second, the roles among the indices changed according to market conditions, with COVID-19 causing the BPI to change from a net receiver to a net transmitter in the short term and the BSI in the long term, affecting net spillover connectedness. Third, it was observed that long-term connectivity tended to increase more than short-term connectedness under extreme conditions. Fourth, the phenomenon of strengthened connectedness under extreme market conditions was confirmed. These results provide important insights into understanding short-term market shocks and long-term stability trends, demonstrating that the connectedness among dry bulk carrier markets strengthens in global crisis situations such as COVID-19. This provides a basis for assessing the resilience and vulnerability of the shipping market and offers useful information for investors and policymakers in crisis management and investment strategy formulation.

Ecological Studies on the Transition of Sheath Blight of Rice in Korea (한국(韓國)에서의 벼 잎집무늬마름병 발생변동(發生變動)에 관(關)한 생태학적(生態學的) 연구(硏究))

  • Yu, Seung-hun
    • Korean Journal of Agricultural Science
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    • v.4 no.2
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    • pp.283-316
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    • 1977
  • In an attempt to obtain a basic information to develop an effective integrated system of controlling sheath blight of rice in Korea, the transition of this disease, the variation of cultural characters and pathogenicity of the pathogen, environmental conditions affecting the disease outbreak and varietal resistance have been investigated. 1. Rice sheath blight which has been minor disease in the past was widely spread, especially since 1971. This disease has promptly spread all over the country and infected 65.2% of total rice growing area in 1976. Various factors are considered to be related to such transition of this disease. Above all, increace of application of nitrogenous fertilizer, early season and earlier cultivation of rice, introduction of more susceptible "Tongil" varieties etc. must be important factors influencing the outbreak of this disease. 2. Great variations in cultural characteristics-such as mycelial growth rate, color of the medium, amount of the aerial mycelium, shape and color of the sclerotia- and in the pathogenicity of isolates of the pathogen, Thanatephorus cucumeris Dank were observed. The optimum temperature for mycelial growth also varied with isolates, from $25^{\circ}C$ to $30^{\circ}C$. There were not necessarily any correlation between curtural characteristics and pathogenicity of isolates of Thanatephorus cucumens. 3. Mycelial grow th of isolates of Thanatephorus cucumens on the PDA medium were correlated with the air temperatures of the region where the isolates were collected. The isolates from the regions with high temperature grew well on PDA medium at $35^{\circ}C$ than those from the region with low temperature, on the other hand, the isolates from the regions with the low temperature grew well on the same medium at $12^{\circ}C$ than those from the regions with high temperature. 4. Pectin polygalacturonase (PG) and cellulase (Cx) were most active on the 3rd day after inoculation on the leaves of rice plant with Thanatephorus cucumeris, whereas pectin methylestrase (PE) was most active on the 4th day after inoculation. Relationship between the activities of PE of isolates and the strength of pathogenicity of isolates was obtained, but PG and cellulase activities were not correlated with pathogenicity of isolates. 5. The tolerence of sclerotia from in-vitro culture to low temperature varied with their water content, the dried cultural sclerotia were more tolerent than wet ones, Dried cultural sclerotia maintained almost 100% germinability for 45 days at $-20^{\circ}C$, whereas wet sclerotia lost viability at $-5^{\circ}C$. The germination ratio of the sclerotia after overwintering changed from 18% to 70% according to the water content of the test paddy fields and the ratio was low in wet paddy condition. 6. To investigate the host range of this fungi in and near paddy field, 17 weeds were inoculated with fungi. The lesions of sheath blight disease was obserbed on Sagittaria trifolia L., Echinochloa crusgalli P. Beauv., Monochoria vaginal is Presl, Polygonum Hydropiper L., Eclipta prostrata L., Digitaria sanguinalis Scapoli. 7. When the level of nitrogen applied was doubled over standard level, total nitrogen content in rice sheath increased, ami when silicate was applied, starch content in rice sheath decreased, inducing the rice plants more susceptible to sheath blight disease. Increased dressing of potash ferilizer reduced the incidence of sheat blight disease. 8. The percentage of infected stems in the early period increased more in the narrow hill plot than in the wide hill plot, but in the late period this tendency was inversed; the percentage of infected stems as well as severity in the wide hill plot increased more compared to the narrow hill plot, and the disease severity in the one plant per hill plot was also low. The number of stems in the wide hill plot was more than the number of stems in the narrow hill plot. This indicates that the microclimate, such as the relative humidity, in the narrow hill plot was more favorable for the development of this disease. 9. There was a high negative correlation between the disease severity of varieties to the sheath blight and the maturity of the varieties, that is, the early varieties were more susceptible than the late ones, and much-tillering varieties usually showed more infection than less tillering varieties. 10. No relationship was obtained between the percentage of infected stems in the early period and the severity after heading, whereas a distinct relationship was obtained between former and latter after Aug. 10.

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Epidemiology and Clincal Analysis of Acute Viral Respiratory Tract Infections in Children(September, 1998-May, 2003) (소아 급성 바이러스성 하기도 감염의 유행 및 임상양상 (1998년 9월-2003년 5월))

  • Lee, Su-Jin;Shin, Eon-Woo;Park, Eun-Young;Oh, Pil-Soo;Kim, Kwang-Nam;Yoon, Hae-Sun;Lee, Kyu-Man
    • Clinical and Experimental Pediatrics
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    • v.48 no.3
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    • pp.266-275
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    • 2005
  • Purpose : Acute respiratory tract infections are the most common illnesses in children. The great majority of these infections involving lower respiratory tracts infections(LRTIs) are caused by respiratory viruses such as respiratory syncytial virus(RSV), parainfluenza virus(PIV), influenza virus (Flu), and adenovirus(ADV), etc. Our purpose was to determine seasonal epidemiology and clinical characteristic features of each viral infection. Methods : Nasopharyngeal aspirate(NPA)s were collected from 4,554 hospitalized children diagnosed as LRTIs on the first day of admission. The study period was from September 1998(Autumn) through May 2003(Spring). Respiratory viruses were detected in 881(19 percent) cases by isolation of the virus or by antigen detection method using indirect immunofluorescent staining. We reviewed the medical records of 837 cases retrospectively. Results : The identified pathogens were RSV in 485 cases(55 percent), PIV in 152 cases(17 percent), FluA in 114 cases(13 percent), ADV in 79 cases(9 percent) and FluB in 51 cases(6 percent). Outbreaks of RSV occurred every year, mostly in the November through December period and of PIV in the April through June period. LRTIs by FluA reached the highest level in January, 2002. FluB infection showed an outbreak in April, 2002. The clinical diagnoses of viral LRTIs were bronchiolitis in 395 cases(47 percent), pneumonia in 305 cases(36 percent), croup in 73 cases(9 percent) and tracheobronchitis in 64 cases(8 percent). Conclusion : Viruses are one of the major etiologic agents of acute LRTIs in chidren. Therefore, we must continue to study their seasonal occurrence and clinical features to focus on management, and also for reasons of prevention.

A study on Huh-Joon's medical thoughts in Dong-Eui-Bo-Kham (동의보감(東醫寶鑑)을 통한 허준의 의학사상에 관한 고찰)

  • Kwon, Hak-Cheol;Park, Chan-Guk
    • Journal of Korean Medical classics
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    • v.6
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    • pp.89-130
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    • 1993
  • Huh-joon's medical thoughts shown on his medical book of the Doog-Eui-Bo-Kham can be summerized as follows. 1. The general trend of medical science in Koryo dynasty is that much more interests were concentrated upon the books about curative means rather than upon the books about theoretical knowledge of medical science. With the development of Hyang Yak(鄕樂) (the term referring either various kinds of domestic medical stuffs such as herbs or the curative methods using those stuffs) and the writing of books on Hyang Yak, independent medical science of the nation's own was established in late Koryo dynasty. And the national medical science was continuously further developed until early Choson dynasty. Briskly-expanded mutual exchanges with China in early Choson dynasty provided Choson opportunities to import Chinese medical science and to examine it. Under this circumstances, he wrote the Dong-Eui-Bo-Kham. 2. As we look over the preface and Chip-Rae-Muo(集例文), we can find the characterstic of Doog-Eui-Bo-Kham is that the philosophical theory of Taoism was quoted in explaining the principles of his medical science and that the main idea of Naekyuog is the basis in explaining the way of curing diseases. 3. 83 kinds of medical books were quoted in the Doog-Eui-Bo-Kham. Besides, as many as 200 kinds of books including Tao-tzu's teaching books(道書), history books(史書), almanac(曆書), and Confucius' teaching books(儒家書籍) were quoted in total. Naekyuog and Eue-Hak-Ip-Mun, Dan-Kye-Sim-Bup were the most frequently quoted books among them. 4. Huh-Joon's medical thoughts about health care were like these. 1) The reason why Huh-Joon regarded the idea of health care as of great importance was that he laid much more emphasises on the preventive medicines rather than on the remedial medicines. The direct reason was that he was greatly influenced by profound knowledge of Taoist's study of discipline and who participated in the editing the books from the beginning. 2) Huh-Joon's outlook on human body started from the theory of "Unity of Heaven and Man"(天人合一論), which implied man was a kind of miniature universe. In addition to that, he largely theory of essence(精), vital force(氣), and spirit(神) which were regarded very important as the three most valuable properties in Taoism. However, he took his medical ground on practical and pragmatic idea that he did not discuss fundamental essence(元精), fundamental vital force(元氣), and fundamental spirit(元神) which were given by Heaven from the received only the theory of essence, vital force, and spirit which were acquired after birth and worked mainly on realistic activity of life. 3) Huh-loon accepted Do-In-Bup(導引法) sharply as a method to prevent and cure diseases. 5. Huh-loon's medical thoughts on remedial aspects are as 1) Naekyung was considered so important in Dong-Eui-Bo-Kham that not only each paragraph was begun with the Quotations from Nackyung but also the edited order of the content of the book the same with that of Naekyung. And differently from the former korean medical books he accepted at large and recorded the theories of the four noted physicians of the Geum-Won era(金元四大家) by Dong-Eui-Bo-Kham. 2) For the first time, Huh-Joon introduced the theory of Un-Ki (運氣論) in the Dong-Eui-Bo-Kahm. However, he accepted it as a pathological function of human body but he did not apply physical constitution, physiological function, pathological function, and remedial methods. 3) Huh-loon liked to use Hyang Yak that he recorded korean name of Hyang Yak(鄕名), places of the production(産地), the time of collecting(採取時月), and the way of drying herbs(陰陽乾正法) in the remedial method of a single medicine prescription for diseases at the end of each paragraph. By doing so, he developed, arranged, and revived Hyang Yak. 4) He believed that since the natural features of China were different from those of Korea the reasons of being attacked with its remedial methods couldn't be the same with different from Chinese medical books which primarily focused on paralysis and the injury of the cold has his own structure in his book that he founded independent science of this nation. He consulted enormous documents He discovered and wrote the theory and therefore concrete methods for diseases so that the book hadthe principles of outbreak of diseases(理), methods of cure(法), prescription(方), and a single medicine prescription(藥) and set system of medical science in a good order. By doing so, he and pragmatic development of medical science.

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Effects of Green Manure Crops on Growth and Yield of Carrot for Reduction of Continuous Cropping Injury of Carrot through Crop Rotation (당근 연작장해 경감을 위한 녹비작물 재배가 당근 생육 및 수량에 미치는 영향)

  • Kim, Seong-Heon;Seo, Dong-Cheol;Park, Jong-Hwan;Lee, Seong-Tae;Lee, Sang-Won;Kim, Hong-Chul;Cho, Ju-Sik;Heo, Jong-Soo
    • Korean Journal of Environmental Agriculture
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    • v.32 no.4
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    • pp.279-286
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    • 2013
  • BACKGROUND: Soil incorporation of green manure crop(GMC) is one of the methods for reducing continuous cropping injury and increasing yield of carrot. The purpose of this study was to evaluate the effects of green manure crops on growth and yield of carrot for reduction of continuous cropping injury of carrot through crop rotation. METHODS AND RESULTS: To reduce the injury by continuous cropping system(CCS) of carrot cultivation, GMCs such as crotalaria and sudangrass were applied, which GMC was sowed in latter-June and returned to soil in latter-October. Nutrient contributions of N, $P_2O_5$, $K_2O$, CaO, and MgO in crotalaria were 8.3, 7.5, 4.4, 7.8, and 2.1 kg/10a, respectively. Nutrient contributions of N, $P_2O_5$, $K_2O$, CaO, and MgO in sudangrass were 8.4, 8.6, 26.8, 0.3, and 2.7 kg/10a, respectively. After incorporation of GMCs into soil, bulk density in soil with GMCs was lower than that in soil without GMCs(control). In soil after incorporation of GMCs, pH was not different in all treatment conditions, and ranged from 6.37~6.64. EC in soil after incorporation of GMCs was lower than that in soil without GMCs. The OM, T-N, and avail. $P_2O_5$ contents in soil with GMCs were higher than those in soil without GMCs. The growth and yields were increased as 39.2%(6,226 kg/10a) in the rotational cropping system(RCS) as compared to continuous cropping system(control and without NPK) of 4,473 kg/10a. Crotalaria cultivation were the most effective crop for reducing the injury of continuous cropping of carrot. CONCLUSION(S): This study suggest that the RCS using GMCs showed lower disease outbreak density in soil for carrot cultivation as compared to CCS without GMCs. Especially, the GMCs good effect for reduction of continuous cropping injury of carrot.

Aviation Safety Regulation and ICAO's Response to Emerging Issues (항공안전규제와 새로운 이슈에 대한 ICAO의 대응)

  • Shin, Dong-Chun
    • The Korean Journal of Air & Space Law and Policy
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    • v.30 no.1
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    • pp.207-244
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    • 2015
  • Aviation safety is the stage in which the risk of harm to persons or of property damage is reduced to, and maintained at or below, an acceptable level through a continuing process of hazard identification and risk management. Many accidents and incidents have been taking place since 2014, while there had been relatively safer skies before 2014. International civil aviation community has been exerting great efforts to deal with these emerging issues, thus enhancing and ensuring safety throughout the world over the years. The Preamble of the Chicago Convention emphasizes safety and order of international air transport, and so many Articles in the Convention are related to the safety. Furthermore, most of the Annexes to the Convention are International Standards and Recommended Practices pertaining to the safety. In particular, Annex 19, which was promulgated in Nov. 2013, dealing with safety management system. ICAO, as law-making body, has Air Navigation Commission, Council, Assembly to deliberate and make decisions regarding safety issues. It is also implementing USOAP and USAP to supervise safety functions of member States. After MH 370 disappeared in 2014, ICAO is developing Global Tracking System whereby there should be no loophole in tracking the location of aircraft anywhere in world with the information provided by many stakeholders concerned. MH 17 accident drove ICAO to install web-based repository where information relating to the operation in conflict zones is provided and shared. In addition, ICAO has been initiating various solutions to emerging issues such as ebola outbreak and operation under extreme meteorological conditions. Considering the necessity of protection and sharing of safety data and information to enhance safety level, ICAO is now suggesting enhanced provisions to do so, and getting feedback from member States. It has been observed that ICAO has been approaching issues towards problem-solving from four different dimensions. First regarding time, it analyses past experiences and best practices, and make solutions in short, mid and long terms. Second, from space perspective, ICAO covers States, region and the world as a whole. Third, regarding stakeholders it consults with and hear from as many entities as it could, including airlines, airports, community, consumers, manufacturers, air traffic control centers, air navigation service providers, industry and insurers. Last not but least, in terms of regulatory changes, it identifies best practices, guidance materials and provisions which could become standards and recommended practices.

PRC Maritime Operational Capability and the Task for the ROK Military (중국군의 해양작전능력과 한국군의 과제)

  • Kim, Min-Seok
    • Strategy21
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    • s.33
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    • pp.65-112
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    • 2014
  • Recent trends show that the PRC has stepped aside its "army-centered approach" and placed greater emphasis on its Navy and Air Force for a wider range of operations, thereby reducing its ground force and harnessing its economic power and military technology into naval development. A quantitative growth of the PLA Navy itself is no surprise as this is not a recent phenomenon. Now is the time to pay closer attention to the level of PRC naval force's performance and the extent of its warfighting capacity in the maritime domain. It is also worth asking what China can do with its widening naval power foundation. In short, it is time to delve into several possible scenarios I which the PRC poses a real threat. With this in mind, in Section Two the paper seeks to observe the construction progress of PRC's naval power and its future prospects up to the year 2020, and categorize time frame according to its major force improvement trends. By analyzing qualitative improvements made over time, such as the scale of investment and the number of ships compared to increase in displacement (tonnage), this paper attempts to identify salient features in the construction of naval power. Chapter Three sets out performance evaluation on each type of PRC naval ships as well as capabilities of the Navy, Air Force, the Second Artillery (i.e., strategic missile forces) and satellites that could support maritime warfare. Finall, the concluding chapter estimates the PRC's maritime warfighting capability as anticipated in respective conflict scenarios, and considers its impact on the Korean Peninsula and proposes the directions ROK should steer in response. First of all, since the 1980s the PRC navy has undergone transitions as the focus of its military strategic outlook shifted from ground warfare to maritime warfare, and within 30 years of its effort to construct naval power while greatly reducing the size of its ground forces, the PRC has succeeded in building its naval power next to the U.S.'s in the world in terms of number, with acquisition of an aircraft carrier, Chinese-version of the Aegis, submarines and so on. The PRC also enjoys great potentials to qualitatively develop its forces such as indigenous aircraft carriers, next-generation strategic submarines, next-generation destroyers and so forth, which is possible because the PRC has accumulated its independent production capabilities in the process of its 30-year-long efforts. Secondly, one could argue that ROK still has its chances of coping with the PRC in naval power since, despite its continuous efforts, many estimate that the PRC naval force is roughly ten or more years behind that of superpowers such as the U.S., on areas including radar detection capability, EW capability, C4I and data-link systems, doctrines on force employment as well as tactics, and such gap cannot be easily overcome. The most probable scenarios involving the PRC in sea areas surrounding the Korean Peninsula are: first, upon the outbreak of war in the peninsula, the PRC may pursue military intervention through sea, thereby undermining efforts of the ROK-U.S. combined operations; second, ROK-PRC or PRC-Japan conflicts over maritime jurisdiction or ownership over the Senkaku/Diaoyu islands could inflict damage to ROK territorial sovereignty or economic gains. The PRC would likely attempt to resolve the conflict employing blitzkrieg tactics before U.S. forces arrive on the scene, while at the same time delaying and denying access of the incoming U.S. forces. If this proves unattainable, the PRC could take a course of action adopting "long-term attrition warfare," thus weakening its enemy's sustainability. All in all, thiss paper makes three proposals on how the ROK should respond. First, modern warfare as well as the emergent future warfare demonstrates that the center stage of battle is no longer the domestic territory, but rather further away into the sea and space. In this respect, the ROKN should take advantage of the distinct feature of battle space on the peninsula, which is surrounded by the seas, and obtain capabilities to intercept more than 50 percent of the enemy's ballistic missiles, including those of North Korea. In tandem with this capacity, employment of a large scale of UAV/F Carrier for Kill Chain operations should enhance effectiveness. This is because conditions are more favorable to defend from sea, on matters concerning accuracy rates against enemy targets, minimized threat of friendly damage, and cost effectiveness. Second, to maintain readiness for a North Korean crisis where timely deployment of US forces is not possible, the ROKN ought to obtain capabilities to hold the enemy attack at bay while deterring PRC naval intervention. It is also argued that ROKN should strengthen its power so as to protect national interests in the seas surrounding the peninsula without support from the USN, should ROK-PRC or ROK-Japan conflict arise concerning maritime jurisprudence. Third, the ROK should fortify infrastructures for independent construction of naval power and expand its R&D efforts, and for this purpose, the ROK should make the most of the advantages stemming from the ROK-U.S. alliance inducing active support from the United States. The rationale behind this argument is that while it is strategically effective to rely on alliance or jump on the bandwagon, the ultimate goal is always to acquire an independent response capability as much as possible.

Ichthyotoxic Cochlodinium polykrikoides red tides offshore in the South Sea, Korea in 2014: I. Temporal variations in three-dimensional distributions of red-tide organisms and environmental factors

  • Jeong, Hae Jin;Lim, An Suk;Lee, Kitack;Lee, Moo Joon;Seong, Kyeong Ah;Kang, Nam Seon;Jang, Se Hyeon;Lee, Kyung Ha;Lee, Sung Yeon;Kim, Mi Ok;Kim, Ji Hye;Kwon, Ji Eun;Kang, Hee Chang;Kim, Jae Seong;Yih, Wonho;Shin, Kyoungsoon;Jang, Poong Kook;Ryu, Joo-Hyung;Kim, Sung Young;Park, Jae Yeon;Kim, Kwang Young
    • 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.