동계 대발생한 와편모조류 Heterocapsa triquetra 성장특성

Abstract

To clarify favorable environmental conditions for the population development of dinoflagellate Heterocapsa triquetra, the seasonal abundance of this species and related environmental factors were investigated from May 2007 to May 2008 in Lake Shihwa, Korea. In particular, we focused on: (1) the relationship between population density and abiotic factors in field; (2) modeling the growth as a function of temperature, salinity and nutrient variables in laboratory experiments. In field, the population densities of H. triquetra remained low level during the period from late spring to early summer and completely disappeared from August to November, 2007. The abundance of H. triquetra appeared two peaks during our field investigation. The first reached 585 X 103cells L-1on 17 January and the second reached 672 X 103cells L-1on 28 March 2008, with the water temperatures of 0.9˚C and 9.1˚C, respectively. In laboratory experiments, the growth rates of H. triquetra increased with the temperature increments within a range from 10 to 20˚C. The highest growth rate of H. triquetra reached 0.62 d-1at 20˚C with a salinity of 30. When water temperature was controlled at 25˚C, the dinoflagellate was unable to grow at 10 and 15 salinities, and only reached relatively low growth rates (< 0.12 d-1) in other salinity conditions. When water temperature reached to 30˚C, growth rates of this dinoflagellate at all salinity levels all displayed continuously minus values. However, the dinoflagellate displayed well growth at low temperatures, for example, their cells grew all right even at 5˚C under between 20 and 35 salinity. Under the continuous cultures at 5˚C and 8˚C, the H. triquetra cell abundances gradually increased and retained growth capability for more than 30days, suggesting that H. triquetra grew very well at such very low temperature conditions. These specific characteristics make H. triquetra become an unusual dominant dinoflagellate during cold winter season in the Lake