Responses by phytoplankton communities to temperature elevation in the vicinity of condenser effluent from nuclear power plants and mixotrophic ecology of a newly described dinoflagellate species, Ansanella granifera
원전 온배수 영향 해역 수온 상승에 대한 식물플랑크톤 군집의 반응 및 신규 기재 와편모류 종인 Ansanella granifera의 혼합영양 생태 연구

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자연과학대학 해양학과
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서울대학교 대학원
engulfmentfeedinggrowthingestionmixotrophynuclear power plantphytoplanktonthermal condenser effluent
학위논문 (박사)-- 서울대학교 대학원 : 지구환경과학부 해양학 전공, 2016. 2. 정해진.
The effect of future global warming and climate change on marine ecosystems could be estimated by the ecosystem change in the waters adjacent to the thermal condenser effluent from nuclear power plants. As of the end of 2014, there are 437 nuclear power plants in operation around the world. In Korea, there are 24 units in operation and the temperature rise(△T) across the condenser is about 7~9 ℃.

The effect of warming on phytoplankton communities was analyzed based on data collected from 9 sampling stations in the Hanbit and Hanul nuclear power plant sites where field cruises were carried out seasonally for 11 years since 1999.
To predict the effect of global warming and temperature rise of seawater on marine ecosystems, (1) physicochemical properties of seawater near nuclear power plants were determined, and abundance and biomass of phytoplankton were analyzed. Furthermore, (2) seasonal data were analyzed with respect to temperature rise. (3) Based on the seawater properties and phytoplankton communities, effects of the temperature rise on marine ecosystems were predicted.

Between 1999 to 2009, temperature varied from 2.4 to 37.6℃ in Hanbit site and from 7.8 to 30.2℃ in Hanul site. The Hanbit and Hanul sites showed notable differences in physicochemical properties such as nutrient concentrations, water transparency, and tidal current velocity as well as biological properties such as the composition of dominant phytoplankton groups.

The peaks of diatom biomass were observed at 11℃ and 32℃ for Hanbit, but 4℃ and 20℃ for Hanul. However, peaks for dinoflagellate were observed at higher temperatures than diatom with peaks at 14℃, 29℃ and 35℃ for Hanbit. For Hanul, the biomass of dinoflagellate increased from 14℃ to 20℃ and decreased above 20℃.

The peaks of net-phytoplankton expressed as chlorophyll a concentration were observed at 11℃ and 26-29℃ at both Hanbit and Hanul. At temperatures where the abundances of total phytoplankton were high, the chlorophyll a of net-phytoplankton was the dominant fraction. However, at low temperatures or very high temperatures (above 35℃ in Hanbit), chlorophyll a of nano-phytoplankton was the dominant fraction.

The effect of temperature elevation on the phytoplankton abundance was not always negative. Generally, the phytoplankton abundances at the discharge station was lower than those at intake station. However, in winter, thermal condenser effluent from Hanbit resulted in increased phytoplankton abundances at the discharge station (i.e., positive effect). The water temperature at the Hanbit discharge station varied from 3.3~18.8℃.

Base on the changes in dominant phytoplankton groups associated with increasing water temperature, it is expected that a temperature increase due to global warming may cause increases in the fraction of dinoflagellates relative to the other phytoplankton. Furthermore, dominance by eurythermal and high-temperature adapted planktons is expected.

Thus, present results may provide a basis to better understanding of the effects of thermal discharge effluent on marine ecosystems, especially on abundance and biomass of phytoplankton and predicting changes in marine phytoplankton community due to global warming.

As the one of most remarkable indicators for the rise of seawater temperature, the ratio of dinoflagellates to total phytoplankton was shown to be very important in this study. Thus, revealing the eco-physiological responses of dinoflagellates, in particular new species, to different temperatures is very important.

I explored the growth-associated eco-physiology of a newly described mixotrophic dinoflagellate Ansanella granifera isolated from the water of Shiwha Bay, Korea in 2010. I explored the feeding mechanism and the different types of species that A. granifera was able to feed on. In addition, I measured the growth and ingestion rates of A. granifera feeding on the prasinophyte Pyramimonas sp., the only algal prey, as a function of prey concentration. A. granifera was able to feed on heterotrophic bacteria and the cyanobacterium Synechococcus sp. However, among the 12 species of algal prey offered, A. granifera ingested only Pyramimonas sp. A. granifera ingested the algal prey cell by engulfment. With increasing mean prey concentration, the growth rate of A. granifera feeding on Pyramimonas sp. increased rapidly, but became saturated at a concentration of 434 ng C mL-1 (10,845 cells mL-1). The maximum specific growth rate (i.e., mixotrophic growth) of A. granifera feeding on Pyramimonas sp. was 1.426 d-1, at 20°C under a 14 : 10 h light-dark cycle of 20 μE m-2 s-1, while the growth rate (i.e., phototrophic growth) under similar light conditions without added prey was 0.391 d-1. With increasing mean prey concentration, the ingestion rate of A. granifera feeding on Pyramimonas sp. increased rapidly, but slightly at the concentrations ≥306 ng C mL-1 (7,649 cells mL-1). The maximum ingestion rate of A. granifera feeding on Pyramimonas sp. was 0.97 ng C predator-1 d-1 (24.3 cells grazer-1 d-1). The calculated grazing coefficients for A. granifera feeding on co-occurring Pyramimonas sp. were up to 2.78 d-1. The results of the present study suggest that A. granifera can sometimes have a considerable grazing impact on the population of Pyramimonas spp. Present results on A. granifera may provide a firm basis for the understanding of eco-physiological characteristics of the mixotrophic dinoflagellates and their roles in marine planktonic food webs in marine ecosystems.

Results from this study may be applied to predict the changes in marine phytoplankton community by global warming in the ocean as well as at the coastal waters near nuclear power plants.
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College of Natural Sciences (자연과학대학)Dept. of Earth and Environmental Sciences (지구환경과학부)Theses (Ph.D. / Sc.D._지구환경과학부)
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