南亚热带水库中盔形溞牧食对浮游植物群落影响的围隔试验

An Enclosure Experiment Study of Daphnia galeata Grazing Effects on Phytoplankton in a Subtropical Reservoir

为了解热带-亚热带地区大型枝角类对浮游植物的控制作用,2010年3-4月在广东省流溪河水库进行了围隔试验研究。围隔尺寸4m×4m×6m,用孔径2mm的网过滤库水。设置4个试验组,包括1个对照组(C)和低、中、高密度(L、M、H)的3个梯度处理组,添加的盔形溞(Daphnia galeata)分别为0、0.3、0.6、1.0个/L;每个试验组设3个平行,持续6周。由于盔形溞以孤雌生殖为主,在无鱼条件下,盔形溞在较短的时间内快速建立了较高密度的种群,对照组与处理组之间没有显著的差异。在试验进行至21d,所有围隔中的盔形溞种群达到最大密度,随后出现了明显下降;4个试验组的总浮游植物生物量差异不显著,所有处理中浮游植物和叶绿素a在试验初期出现快速下降。在浮游植物密度下降的同时,其群落组成结构发生了很大的变化。小环藻(Cyclotella me-neghiniana)、卵囊藻(Oocystis lacustris)等细胞直径<30μm的浮游植物种类前期生物量降低后期稳定,而转板藻(Mougeotia)等粒径>30μm的种类后期生物量呈增加趋势。试验结果表明,在热带-亚热带深水贫营养水库中,当盔形溞等大型枝角类种群存在时,通过对鱼类的合理调控,存在有效调控浮游植物密度与结构的可能性。

In order to understand the possibility of suppression of Daphnia on phytoplankton in tropical and subtropical reservoirs, we carried out a fish-free enclosure experiment in Liuxihe Reservoir, southern China from March 6 to April 18, 2010, lasting for 6 weeks. The experiment had one control （C） group without adding D. galeata and three treatment groups （ L, M, H） with adding low, middle and high density of D. galeata. The adding density of D. galeata was 0 ind./L in C, 0.3 ind./L in L, 0.6 ind./L in M and 1.0 ind./L in H. Each treatment had 3 replicates. The results showed that the density of D. galeata increased rapidly in all the treatments, and there was no significant difference between the control and treatment groups. The density of D. galeata reached the peak in the third week and then decreased quickly. Correspondingly, the biomass of phytoplankton decreased in the first two weeks and had significant shift on community structure. The biomass of the size class with diameter 〈 30 p^m decreased with the increased of D. galeata. The size class with diameter 〉 30 Ixm increased towards the end of the experiment. These results indicate that when D. galeata appears abundantly in the tropical and subtropical deep and oligotrophical reservoirs, it is possible to suppress phytoplankton by means of manipulating density of planktivo- rous fish.