2001—2002年粤东柘林湾浮游植物的生态学研究

ECOLOGICAL STUDY ON PHYTOPLANKTON IN ZHELIN BAY,EASTERN GUANGDONG:2001-2002

20 0 1年 7月— 2 0 0 2年 7月对粤东赤潮重灾区柘林湾进行的浮游植物周年调查表明 ,柘林湾共有浮游植物 68属 1 83种。其中硅藻为最优势类群 ,共 5 1属 1 43种 ,占总种数的77.8% ;甲藻 1 1属 34种 ;其它浮游植物类群 6属 6种。调查海区浮游植物群落的种类丰富度、细胞密度、生物多样性和均匀度的平面分布均表现为湾外高于湾内和湾内外侧高于湾内内侧的基本格局 ,但黄冈河河内浮游植物群落的构成却呈现种类少而密度高的特点。调查期间浮游植物的总细胞数年均值为 1 6.9× 1 0 4 cells/L ,周年变动模式为双峰型 (高峰位于 8月和4月 )。与上一个周年调查 ( 2 0 0 0年 5月— 2 0 0 1年 5月 )的总细胞数年均值 ( 36.0× 1 0 4 cells/L)和单峰型周年变动模式 (最高峰位于 7月 )相比 ,差异较大。这可能是 2 0 0 1— 2 0 0 2年厄尔尼诺现象导致粤东地区气候异常、干旱少雨 ,以及调查海区无机磷剧减 45 %所致。中肋骨条藻(Skeletonemacostatum)为该湾的全年优势种 ,在群落总细胞数中的百分比年均值从上一年度的5 8.7%上升至本年度的 71 .0 % ,导致Shannon Wiener多样性指数从上一年度的 1 .91减少至本年度的 1 .75。中肋骨条藻的绝对占优已在很大程度上改变了该湾浮游植物的群落结构 ,并使中肋骨条藻赤潮的发生?

Phytoplankton in the Zhelin Bay, eastern Guangdong, where the harmful algal blooms most frequently occurred, was investigated from July 2001 to July 2002. The results show that there were 183 species in total, representing 68 genera. Among these, diatoms (143 species, representing 51 genera) accounted for 77.8%, followed by dinoflagellates, with 34 species representing 11 genera. The species richness, abundance, diversity and evenness of phytoplankton at the outside of the bay were higher than inside. Within the bay, higher values were observed in the outer bay than in the inner bay. However, the density of phytoplankton increased from the inside of bay to the outside of bay, and was greater in outer and eastern parts than in the inner and western parts. Such a horizontal distribution pattern was mainly due to the low density and fewer species in the bay. The large scale cage fish culture may explain why the high nutrients could not accommodate high density or more species of phytoplankton. Compared with previous investigations (7/2000-7/2001), the annual density of phytoplankton decreased from 36.0×10 4 cells/L to 16.9×10 4 cells/L, and the density dynamics shifted from mono peak in July to dual peak in August and April. The variation might relate to the El Nino event in 2001-2002, which resulted in low precipitation over eastern Guangdong and the consequent 45% decrease of PO 4 P in Zhelin Bay compared with the previous investigation year. During the present investigation, Skeletonema costatum was the most dominant species, and its percentage in total cell number of phytoplankton increased from 58.7% to 71.0%, which accounted for the decrease of the diversity index from 1.91 of the previous period to 1.75. Dominance of S. costatum has largely changed the hytoplanktonic community in Zhelin Bay and may increase the occurrence of its bloom outbreak. Sewage, large scale mariculture and water exchange are the most important factors to affect the spatial temporal distribution of phytoplankton and driving forces for high nutrients and low phytoplankton densities in Zhelin Bay.