中文摘要：

在海南岛形成春旱时,老爷海潟湖内常常发生网箱养殖鱼类因缺氧(DO【2mg/L或者【30%)而迅速(1—2天内)大规模死亡的事件;然而,其中的缺氧成因至今仍未见相关研究报道。本文在2008—2011年对老爷海执行了7个航次的生物地球化学调查。在形成充沛春雨的2009年春季季风转换期所执行航次(气象条件表现为风速高和多雨)中,很难观察到底层缺氧现象;与此相对应,潟湖水体的垂直稳定度差,浮游植物群落以微微型(【2μm)和微型(2—10μm)藻类占优势。在形成显著春旱的2010年春季季风转换期所执行航次(气象条件表现为微风和少雨)中有大规模底层缺氧形成,缺氧水体从内湾深坑水柱(水深约6m)底层一直蔓延到外湾浅水养殖区;与此相对应,内湾深坑水柱明显层化并形成高盐度生境,浮游植物群落以海洋角管藻(硅藻)占优势,而病毒丰度则达到所有7个航次调查中的最高值。在2008、2009和2011年西南季风盛行期所执行航次(气象条件表现为高温、微风和多雨)中都有小规模底层缺氧形成,且仅局限在内湾深坑底层水中;与此相对应,深坑水柱强烈层化并形成低盐度生境,浮游植物群落以微微型和微型藻类占优势。以上调查结果说明,老爷海潟湖内的底层缺氧规模对上界面的南海季风气候节律有着明显响应;其中,春旱气象条件在潟湖内湾所营造的水柱层化(阻碍复氧)和高盐度生境(有利于硅藻成为浮游植物群落优势种)相耦合,则可促成从潟湖内湾深坑底层一直蔓延到外湾网箱养殖区的大规模底层缺氧现象。

英文摘要：

Hypoxia (DO＜2mg/L or ＜30％) often caused acute mass fish mortality within 1-2 days in cage culture area of Laoyehai Lagoon (Hainan,South China Sea) during spring drought.To understand the causes of hypoxia,we conducted 7 cruises in biogeochemistry in the area during 2008-2011.The 2009 cruise was conducted in spring monsoon transition period during which wind speed was high and rainfall ample,bottom hypoxia was rare; correspondingly,water column was unstable in vertical direction in the whole lagoon,phytoplankton community was dominated by pico-phytoplankton (＜2μm)and nano-phytoplankton (2-10μm) species.The 2010 cruise was in spring monsoon transition period featuring breeze and drought,and bottom hypoxia was common from the deep hole (depth of about 6m) in the inner bay to the cage culture area in the outer bay; correspondingly,water column structure of the deep hole was strongly stratified,phytoplankton community was dominated by diatom Cerataulina pelagica,and virus abundance reached the highest value of all 7 cruises.The cruises conducted in 2008,2009 and 2011 met southwest monsoon periods during which weather was hot with breeze and ample rainfall; bottom hypoxia was in small scale,and the hypoxic water mass was limited to the deep hole; correspondingly,water column structure of the deep hole was highly stratified,phytoplankton community was dominated by pico-phytoplankton (＜2am) and nano-phytoplankton (2-10am) species.These results show that hypoxia phenomena in Laoyehai Lagoon responded clearly to the rhythmic climate change of the South China Sea Monsoon,and to the coupling between the stratification and diatom bloom in water column of the deep hole,which was caused by spring drought and resulted in massive hypoxia spread from the deep hole in the inner bay to the cage culture area of the outer bay.