深圳湾表层沉积物中甲藻孢囊的垂直分布

Vertical distribution of dinoflagellate resting cysts in surface sediments from Shenzhen Bay of the South China Sea

集了深圳湾 3个采样点约 2 0 cm的表层沉积物样品 ,研究了甲藻孢囊的垂直分布。共分析鉴定出孢囊类型 37种 ,其中 5种为我国沿海未报道的新记录类型 ,原多甲藻类孢囊是该海域种类最丰富的孢囊类型。除上表层沉积物外 ,深圳湾甲藻孢囊密度较低 ,孢囊密度大多在 50 0 cysts/ g D Wt以下 ,总孢囊密度变化范围为 83～ 40 36 cysts/ g D Wt之间。锥状斯氏藻是深圳湾甲藻孢囊的优势种类 ,上表层沉积物中该孢囊密度的急剧上升证实了 2 0 0 0年附近海域所发生的该藻赤潮。而裸甲藻类孢囊含量明显比南海其他海域高。孢囊的香农 -威弗种类多样性指数为 1 .50～ 3.96之间 ,并且在非养殖区、离岸海域及较深层次沉积物中较高 ,而孢囊密度则呈相反的变化趋势。种类多样性的下降及孢囊密度的上升在一定程度上说明深圳湾污染的变化趋势 ,富营养化程度非养殖区大于养殖区 ,近岸海域大于离岸海域 。

Three sediment cores about 20cm length were collect ed from Shenzhen Bay, the South China Sea by TFO core sampler in August 2001 to investigate the vertical distribution of dinoflagellate resting cysts. Samples w ere taken every 2cm and treated with palynological process by HCl and HF solutio ns to remove calcium carbonate and silicate minerals respectively. After treated by acid, samples were sonicated and then sieved through 125μm and 20μm metall ic screens, and the materials captured on the latter one were suspended in 10 ml distill water for observation. A total of 37 different cyst types were detected from 30 samples, including 25 t ypes of heterotrophic ones and 12 of autotrophic ones. Five cyst types were the newly recorded cyst species in the China Sea areas. The cyst concentrations were less than 500 cysts/g D Wt in most samples except for sediments of the depth of 0~4cm. While cyst abundance increased rapidly in the upper surface sediment, an d the peak value was at the uppermost layer of the depth of 0~2cm in all station s. Cyst densities ranged from 83 to 4036 cysts/ g D Wt, with an approximate aver age of 1000 cysts/g D Wt in the upper 12cm sediments. Scrippsiella trochoidea was the most dominant and common cyst species in this survey, and was observe d almost in all samples. Meanwhile, the abrupt increase of cysts of S.trochoid ea in the upper surface sediments reflected series blooms of this species in n earby sea areas in 2000, which resulted in 3~5 times increase of concentrations of overall cysts. Protoperidinioid was the most diversified cyst group, in which 20 cyst types were identified. However, there were no significant dominant spec ies in protoperidinioid group. Cysts in gymnodinioid group mainly represented by those of Cochlodinium and Polykrikos were much more abundant in sediments from Shenzhen Bay than other sea regions of the South Chin a Sea, and the abundance of cysts in these two genera was an important character istic of cyst composition in Shenzhen Bay. The values of the Shannon-Weaver div ersity index (H') were between 1 5 and 3 9. Higher values of Shannon-Weaver i ndex were in non-aquacultural area, offshore region and the deeper layers of se diments, whereas, the concentrations of overall cysts and cyst of Scrippsiella trochoidea were quite the contrary. Lower species diversity and higher cyst p roduction indicated the increase of pollution and high primary production. Thus, the results of cyst assemblages showed some trend of changes in water quality i n this area to some extent, and suggested that the trophic level was higher in c ultural, inshore area and the situation became more serious in recent years .