大型枝角类蚤状溞对小型热带湖泊浮游植物群落影响的研究

2006年4月10日至2006年4月22日,采用原位吊瓶实验的方法,在暨南大学校园明湖中进行了大型枝角类蚤状溞(Daphnia pulex)对浮游植物种群变化和群落结构影响的实验。实验初期,明湖浮游植物群落的组成是以飞燕角甲藻(Ceratium hirundinella)和单角盘星藻(Pediastrum simplex)为优势种。在室内将蚤状溞培养至体长2mm以上,将蚤状溞加入到装满湖水的4.5L的透明瓶中,设置4个梯度:0ind(A,对照),10ind.(B),20ind(C)和30ind(D),每个梯度有3个平行,将实验瓶置于水表层50cm处。12d后实验结束,不同处理之间的浮游植物种群数量和组成有了明显的差异。与对照组相比,飞燕角甲藻和颗粒直链藻(Meclosira granulata)密度在实验组B、C和D中下降明显;小环藻(Cyclotella)和栅藻(Scenedesmus)等小型浮游植物在牧食压力比较大的C和D瓶中密度低于对照组,而在牧食压力相对较低的B瓶中,它们的密度高于对照组,这可能是由于蚤状溞加速了水体的营养盐循环反过来促进这些小型浮游植物的生长。处理组中绿藻门的盘星藻数量没有明显的下降,这与盘星藻不能被浮游动物直接滤食有关。实验结果表明蚤状溞对浮游植物的群落数量和组成的影响程度与其自身的种群密度密切相关,也与浮游植物群落结构有关。由于飞燕角甲藻是一种细胞较大的种类,蚤状溞对它的抑制作用主要是通过机械伤害作用实现的。

Effects of large filtering zooplankton-Daphnia pulex on phytoplankton communities in a small tropical Lake

An in situ experiment was carried out to examine the effects of large filtering zooplankton--Daphnia pulex's on phytoplankton community strcuture in a shallow entrophic lake on the campus of Jinan University. Ceratium hirundinella and Pediastrum simplex are dominant and blooming-forming phytoplankton species in this lake. Daphnia pulex were cultured in the laboratory to reach the body-size of 20 mm, then was transfered into the transparent bottles (4.5 L). Four gradients are set:0 ind(A), 10 ind(B), 20 ind(C) and 30 ind(D), with three replications for each concentration gradient. The bottles were tied together and were floated at a depth of 50cm below the surface water in the pond. After 12 days of the experiment, the phytoplankton abundance and composition in the experimental bottles were significantly different among three treatments. The densities of Ceratium hirundinella and Meclosira granulate declined significantly with the increase of the density of D. pulex in those treatments. The densities of Cyclotella and Scenedesmus in the treatment D were very low, but in the treatments B and C, where the predation from D. pulex were low or moderate, phytoplankton abundance were even higher than in the control treatment A; the density of Chloropyhta showed no clear decrease in all the treatments. The results indicated that the impact of the large zooplankton D. pulex on phytoplankton communities is not only closely related to its own population density, but also closely related to phytoplankton species. It can suppress the population abundance of C. hirundinella by a mechanistic damage; For small phytoplankton species, D. pulex can stimulate the their growth by promoting the nutrients cycle when the predation pressure from D. pulex was low or moderate.