Weihong Zhao^*, Jintao Li^§, Dengfeng Yang^§
*Institute of Oceanology ,Chinese Academy of Sciences,Qingdao,266071, ^§Chemistry and Chemical Engineering College, Qingdao Ocean University, Qingdao, 266003

Abstract

Gold Star No.2 took a comprehensive survey in the Changjiang estuary and adjacent areas from July 23rd to August 14th, 2001. During the period, we carried out field cultivation experiments to study the nutrient needs of phytoplanton at C105 (123°E, 32°N), C205 (123°30' E, 31°N) and C304 (123°18'E , 29°40'N) stations.

1. A great scale of Skeletonema costatum blooming was taking place when our ship got to the C105 station which located in the northeast of the Changjiang Estuary , at five past thirteen o'clock on July 27th, 2001. From our experiments, we found chlorophyll-a were very high at the beginning. If culture nutrients without phosphorus or without all nutrients were added to the culture seawater, the chlorophyll-a descended very quickly. Those were caused by depletion of phosphorus after red tide. If no nitrogen or no silicon were added, the chlorophyll-a would not decrease quickly. If all nutrients or without iron were added, the chlorophyll-a kept high level. Those experiments showed that the phytoplankton growth in this area were limited by phosphorus .

2. The second field experiment had been carried out at station C205 on the east of the Changjiang Esturay at five o'clock on July 28th, 2001, where no red tide was taking place. The experiment results showed that phosphorus still was the major limitation factor. Nitrogen became one of limitation factors during the later culture period which is different with the results at C105 station.

3. When we came to the station C304, a great scale of Noctiluca scintiuans red tide were taking place. Because most phytoplankton was eaten up, in first five days chlorophyll-a in the culture seawater were very low. Little phytoplankton at the beginning limited their quick growths. Five days later, the chlorophyll-a began to elevate. The chlorophyll-a kept low in bottles without phosphorus added or without all nutrients add. The chlorophyll-a in bottles without nitrogen or without silicon added were higher than the former. The chlorophyll-a were highest in bottles with all nutrients added or without iron added. The experiments also showed that the phytoplankton growth was limited by phosphorus and Noctiluca scintiuans preying.