얼음속에서 높은 밀도로 출현한 Heterocapsa triquetra의 성장특성

Abstract

To clarify favorable environmental conditions for the population development of dinoflagellate Heterocapsa triquetra, the seasonal abundance of the species and related environmental factors were investigated from May 2007 to May 2008 in a brackish Lake Shihwa, Korea. The growth and morphological characteristics of this species was also examined under laboratory conditions. 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. Interestingly, a dense bloom of H. triquetra below the ice-water interface was appeared on 17 January. The other peaks reached 67 X 104 cells L-1 on 28 March 2008, with the water temperatures of 9.1˚C. 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-1 at 20˚C with a salinity of 30. At above 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. However, under the continuous cultures at 5˚C and 8˚C, the H. triquetra retained growth capability, suggesting that H. triquetra grew very well at such very low temperature conditions. The equivalent spherical diameter (ESD) in H. triquetra did not change markedly between 10 and 25 ˚C, but the ESD was significantly different at 5 ˚C. Also, several cells shed the theca but remain covered with the pellicle wall at 5˚C culture conditions. These specific characteristics make H. triquetra become an unusual dominant dinoflagellate during cold winter season in the Lake Shihwa.