와편모조류 Ceratium furca 와 C.fusus의 연직이동과 세포분열의 역활

Abstract

To better understand the mechanism underlying blooms of the dinoflagellates, Ceratium furca, and Ceratium fusus, we investigated the diel changes of vertical migration, swimming speed, cell volume, and cell division. Diel vertical migration (DVM) of C. furca was observed in the laboratory but C. fusus did not show DVM. C. furca demonstrated a constant DVM rhythm, i.e., their cells began to descend from the surface before the light was extinguished, and ascended into the surface before the light was turned on. The downward and upward migrations of the cells occurred three hours before turning the light on and off, suggesting that the DVM pattern was independent of nutrient concentration. The swimming speeds of C. furca (avg. 250 µm s-1) were always faster than those of C. fusus (avg. 75 µm s-1). In addition, the speeds of C. furca during light periods were faster than those during dark periods, whereas the speeds of C. fusus remained relatively constant. A higher proportion of dividing cells was recorded near dawn (05:00 - 07:00 hr). Cell volumes of C. furca and C. fusus did not markedly change between 12:00 hr and 21:00 hr, but gradually increased until 03:00 hr and then sharply decreased. Furthermore, the cell volume of the two Ceratium species was closely tied to the temporal pattern of cell division. Combining the DVM behavior of the two Ceratium species and cell division timing, showed that only C. furca divided at the bottom, and then moved toward the surface shortly before the dark to light transition. Based on our observations, C. furca would have an ecological advantage due to their DVM activity, since nutrients can be obtained well in the near bottom layers at night, while during the daytime, light present in the nutrient–depleted surface water can be obtained using their high swimming speed. On the other hand, C. fusus, which has no DVM, may be stimulated by low salinity conditions and might be dependent on external environmenta