巢湖春夏季节浮游甲壳动物群落演替的围隔实验研究

Enclosure investigations on the spring-summer successions of crustacean zooplankton community in Lake Chaohu

为研究巢湖浮游甲壳动物春夏季节的群落演替规律,于2012年2月19日至2012年7月24日(22周)在巢湖进行了围隔实验。共设置三个处理组(即A组:鲢鱼+营养盐;B组:鲢鱼+鳙鱼+营养盐;D组:团头鲂+营养盐)和一个对照组(即C组:不添加鱼类和营养盐)。实验共记录浮游甲壳动物14属21种,其中枝角类9属12种,桡足类8属9种。透明溞(Daphnia hyalina)是春季所有围隔的优势种。春季浮游植物生物量和叶绿素a浓度均处于较低水平。夏季以小型枝角类、大型中镖水蚤(Sinodiaptomus sarsi)和剑水蚤占优势,其密度在围隔A、B和C中较低。夏季所有围隔中的Daphnia种群均消失。在没有蓝藻水华和滤食性鱼类存在下,大型枝角类Daphnia仍然被小型枝角类和桡足类所取代。结果显示,鱼类和营养盐共同决定了巢湖围隔浮游甲壳动物群落结构的季节变化。春季较高的Daphnia种群密度也是巢湖Daphnia仲夏消失的重要原因。

From February 19 to July 24, 2012, the enclosure experiments were conducted in Lake Chaohu to study the spring-summer successions of crustacean zooplankton community. There were three treatment groups（A： Hypophthalmichthys molitrix ＋ nutrients; B： H. molitrix＋Aristichthys nobilis＋ nutrients; D： Megalobrama amblycephale＋ nutrients） and the control group（C： no fish or nutrients）. A total of 21 species belonging to 14 genera were recorded, among which 12 species（9 genera） were cladocerans and 9 species（8 genera） were copepoda. In spring, Daphnia hyalina was the dominant species in all enclosures. Both phytoplankton biomass and chlorophyll a concentration were at a low level in spring. Small cladocerans, Sinodiaptomus sarsi and cyclops were dominant in summer, but their densities were lower in the A, B and C enclosures. Daphnia disappeared in summer in all enclosures. The enclosure experiments showed that large-bodied Daphnia were still replaced by small cladocerans and copepoda despite the absence of cyanobacterial blooms and filtering-fish. The results suggested that fish and nutrients determined seasonal successions of crustacean zooplankton in Lake Chaohu together, and higher population density of Daphnia in spring was also an important factor for mid-summer decline of Daphnia. Moreover, the decrease of small algae biomass might be an important reason for the midsummer decline of Daphnia in Lake Chaohu Lake, while S. sarsi was significantly inhibited by the prey of filtering-fishes.