The Diurnal Fluctuation Of Phytoplankton Communities/assemblages Vertical Distribution At Anchor Stations In China Sea Waters

This thesis reports time series studies on the vertical distribution fluctuation of phytoplankton communities / assemblages by the Uterm?hl method at 11 anchor stations in China Sea Waters. It describes the species composition, dominant species composition, cell abundance, and the spatial-temporal distribution of these at each stations.The thesis is composed of four parts. The first part is a study of the spatial-temporal distribution of phytoplankton assemblages at three anchor stations , which was carried out from October 2006 to November 2006. These stations which were adjacent to the Yellow Sea Cold Water Mass, were nominated LST-7(124o30′E, 36oN), LST-15(122oE, 35oN) and LST-30(123o30′E, 33oN). It is obviously that from station LST-7, station LST-15 to station LST-30, cell abundance and the percentage of diatom increased, and the predominant species was Gymnodinium sp., Thalassiosira nordenskioldii and Trichodesmium thiebautii respectively. At station LST-7 and LST-15 the vertical distribution of cell abundance characterized by lower from surface to 30 m water layer and higher slightly in bottom; on the contrary cell abundance of dinoflagellate showed an decrease tendency from above 30 m water layer to deeper water. The cell abundance fluctuated according to time, with two peaks at 12:00 19th Oct and 0:00 20th Oct in surface and bottom water layers, but compared to the surface and the bottom, two peaks in 10 m water layer were 3 hr later.The second part of this thesis was worked on diurnal vertical phytoplankton distribution at station BM1(123°32′E, 34°27′N), station BM2(123o28′E, 35o30′N) and station BM3(123o20′E, 34oN) in the southern Yellow Sea in April, 2007, orderly. The result shows that from stations BM1 to BM2 , to BM3 cell abundance decreased gradually, which indicated the declining of the bloom of Skeletonema costatum. During the period of cruise S. costatum was the predominant species all the time, Diatom was the predominant group all along, and the percentage of dinoflagellate reduced gradually from stations BM2 to BM1, to BM3. The characteristics of vertical distribution showed that cell abundance at station BM1 existed evenly and steadily from surface to bottom, then a high abundance of phytoplankton occurred below surface at BM2 station, and the high abundance of phytoplankton appeared in deeper water evidently at station BM3 compared to station BM2. Furthermore, diatom and dinoflagellate complemented each other according to time, especially at station BM3.The third part of this thesis was carried out at stations QYQ-1(123o7′E, 32o23′N) and QYQ-2(123oE, 31oN) which were adjacent to hypoxia area in the East China Sea in August and October, 2006. The total cell abundance of phytoplankton was higher in August than in October, and higher in south part of survey area than that of north. Diatom was the predominant group at the two stations. From August to October 2006, there was a predominant species changes at station QYQ-1 from Dactyliosolen fragilissimus to Trichodesmium thiebautii, and from Pseudo-nitzschia pungens to Chaetoceros sp. at station QYQ-2, respectively. In August the vertical distribution of cell abundance characterized by stratification phenomenon - decreased apparently from above 10 m water layer to bottom on the two stations. Furthermore in October the stratification phenomenon was weakened at station QYQ-2, but disappeared at station QYQ-1. According to diurnal dynamics there were two peaks of cell abundance at station QYQ-2, on the other hand, cell abundance of diatom and dinoflagellate complemented each other at station QYQ-1.The fourth part of this thesis investigated the characteristics of phytoplankton assemblage at anchor station TS1 (111o45′E, 14o15′N) from 23rd August to 26th August 2007 in the South China Sea. The result shows that the predominant groups were dinoflagellate and diatom. The predominant species was Trichodesmium thiebautii, mostly detected above 100 m layer, which accounted for 76.777 % of total cell abundance of phytoplankton. The maximum cell abundance appeared at surface water, and with the increase in depth, the cell abundance decreased gradually. The high abundance of dinoflagellate and diatom exsited from surface to 50 m water layer and from 25 m to 100 m water layer, respectively. And the predominant species composition above and below 50 m water layer was mainly composed of dinoflagellate or diatoms separately. At surface cell abundance of Trichodesmium thiebautii fluctuated with time obviously.Based on these studies, the major point of this thesis is that: the vertical distribution of phytoplankton at anchor stations reflected the synthetic effects among phytoplankton intra- and inter-species relationship and environmental factors. According to time course, diurnal fluctuation of phytoplankton assemblage occurred. Nevertheless the heterogenic distribution pattern shows the different adaptation strategies intrinsic properties of phytoplankton species. And the predominant species influenced the phytoplankton assemblages heavily, the major environmental factors which affect the structure of phytoplankton communities and assemblies are different at these anchor stations.