【作者】 赵帅营；

【导师】 韩博平；

【作者基本信息】 暨南大学 ， 水生生物学， 2009， 博士

【摘要】 在温带淡水生态系统,Daphnia是常见的牧食性大型枝角类,由于它对浮游植物较高的牧食率,被认为是级联反应的关键种类。通过改变水体中鱼类(常为肉食性鱼类)的生物量,常常会实现它们对浮游生物的强烈级联反应。在热带及南亚热带淡水水体,往往不存在Daphnia或丰度很低,导致热带及南亚热带与温带淡水水体在生态系统结构和响应模式上存在较大差异。热带及南亚热带水体因缺少Daphnia或丰度较低被认为级联反应会减弱,在热带及南亚热带水体中广泛分布的滤食性鱼类也被认为会影响级联反应的作用强度,但关于这两方面的研究较少。为认识我国南亚热带淡水水体食物链中的浮游动物关键种类,了解级联反应在这些水体中的作用强度,以及探讨滤食性鱼类在不同营养水平下对浮游生物群落的影响,本论文首先详细分析了广东省大型贫营养水库——新丰江水库浮游动物群落及关键种类之间的关系,以此为基础,于2008年4—6月份在同一流域的大型贫—中营养水库——流溪河水库进行了大型围隔(体积约为85 m~3)实验。围隔实验共分两部分:1.添加营养盐往围隔中分三个梯度添加营养盐,分别是低浓度营养盐(P浓度为30μg/L)、中等浓度营养盐(P浓度为60μg/L)和高浓度营养盐(P浓度为90μg/L),所有的N/P(质量比)都是10/1。2.添加营养盐和鲢除添加上述浓度营养盐外,每个梯度均添加4g/m~3的鲢。选一组作为对照,每个处理有3个平行,共有21个围隔。通过比较添加营养盐组与空白组,分析了浮游生物对营养盐的响应;将同时添加鲢和营养盐组与无鱼组做比较,分析了鱼对浮游生物的作用。新丰江水库的后生浮游动物主要为广布性种类,优势类群是桡足类,其幼体的丰度高于成体,优势种为舌状叶镖水蚤、温中剑水蚤和博平近剑水蚤。枝角类中存在大型种类盔形溞,但优势种为长额象鼻溞、奥氏秀体溞和角突网纹溞。轮虫优势种为个体较小的螺形龟甲轮虫和彩胃轮虫。优势种的个体大小为50-1400μm,个体最大的是舌状叶镖水蚤,平均体长为1190μm,个体最小的是彩胃轮虫,平均体长为80μm。浮游植物较低的生物量和鱼类捕食是影响浮游动物的主要因素。作为大型深水水体,新丰江水库的浮游动物群落在华南地区具有代表性。在大型围隔实验中,无鱼情况下添加三个梯度的营养盐均使浮游植物丰度和生物量显著升高,鱼的存在也使浮游植物丰度和生物量明显增加,高于实验中添加的最低营养盐浓度,无论有鱼还是无鱼组内变化均不显著。从生物量来看,在添加营养盐的无鱼组中,浮游植物的优势种从开始的硅藻和甲藻为主演替到硅藻为主,中间又转变为隐藻,最后是以绿藻门的锚藻占优势;在有鱼组内,浮游植物优势种的变化开始时与无鱼组较为相似,但最后是以绿藻门的小球藻占优势。从浮游植物的大小结构来看,只添加营养盐组在实验前期是以小于10μm的种类为主,最后两周内是大于30μm的种类占优势;而在有鱼组,随着实验进行,大于10μm的个体逐渐减少,小于10μm的种类生物量越来越占优势,到实验后期达到最大值。在无鱼情况下,添加营养盐使浮游动物的丰度和生物量都显著增加,而添加营养盐情况下,鱼的存在对浮游动物丰度无显著影响,但使浮游动物生物量显著降低。从浮游动物优势种来看,在无鱼情况下,添加营养盐使舌状叶镖水蚤和盔形溞的丰度及生物量均明显增加,而添加营养盐情况下,鲢的存在令枝角类尤其是盔形溞丰度和生物量显著降低,但对舌状叶镖水蚤的丰度和生物量无明显影响。此外,添加营养盐对轮虫丰度无明显作用,而添加营养盐情况下,鱼的存在使轮虫丰度增加。空白组浮游动物从最初的盔形溞占优势逐渐演替为舌状叶镖水蚤及其桡足幼体占优势。上述结果表明,在我国南亚热带水库中,当鱼类生物量较低或不存在时,Daphnia有可能成为优势种群。在富营养化过程中,滤食性鱼类的存在并没有降低级联反应的强度,因此,滤食性鱼类在南亚热带贫营养和中营养水体中对生态系统的影响及其管理要给予足够的重视。更多还原

【Abstract】 In temperate lakes and reservoirs,the members of genus Daphnia are common and often dominate in zooplankton community.Beacause they can graze phytoplankton heavyly,they are considered as keystone species for significant trophic cascades interaction and successful biomanipulation.In tropics and southern subtropics,the genus Daphnia is often absent or owns very low abundance in the freshwater.Filter-feeding fishes are common and suggested to have significant effects in structuring zooplankton and ecosystems.However,few in situ experiments have been done to further testify this idea.In order to understand the ecological mechanisms of Daphnia distribution and evaluate the strength oftrophic cascade effects in tropical and southern subtropical freshwater water,and also to recognize the effects of the filter-feeding fish on plankton community under different nutrient levels,we first reanalyzed zooplankton community in a large oligotrophic reservoir: Xingfenjiang Reservoir,and then carried out a large-scale enclosure experiment with volume of 85 m~3 in Liuxihe Reservoir,an oligo-mesotrophic water body located in the same catchment, from April to June,2008.The experiment consisted of two parts:1.adding nutrients to enclosure with three gradients,namely,low nutrient level(P concentration:30μg/L),medium nutrient level (P concentration:60μg/L) and high nutrient level(P concentration:90μg/L),with a N/P(mass ratio) of 10/1 in all treatments.2.adding filter-feeding fish with a biomass of 4g/m~3 to each enclosure in addition to the above-mentioned three nutrient levels.There are three replicates for each treatment and 21 enclosures in all.The response of plankton to nutrient enrichment was analyzed through the nutrient enriched treatments and controls.Top-down effects of filter-feeding fish on plankton were analyzed between the fish addition and only nutrient enriched treatments. In the Xingfengjiang Reservoir,zooplankton was mainly composed of eurythermal species. The zooplankton were dominated by copepods,such as Phyllodiaptomus tunguidus, Mesocyclops thermocyclopoides and Tropocyclops bopingi.Daphnia was observed,but cladocerans were mainly composed of Bosmina longirostris,Diaphanosoma orghidani and Ceriodaphnia cornuta.Bosmina longirostris had the highest abundance in the cladocerans,and its dominance was probably related to the species’ adaption to oligotrophic condoition and being free of invertebrate predation.Rotifer’s dominant species were Keratella cochlearis and Chromogaster sp..The body lengths of the zooplankton in the reservoir range from 50μm to 1400μm.The largest dominant species was Phyllodiaptomus tunguidus with an average length of 1190μm.In December,perhaps due to the Neosalanx taihuensis Chen’s heavy predation,the abundance and biomass of Phyllodiaptomus tunguidus were less than in the other sampling periods.The dominance of Phyllodiaptomus tunguidus in the reservoir were probably related to it’s low threshold food concentration and efficient filtering mode in comparison with Daphnia galeata.In viewpoint of the specific composition,the zooplankton has a typical identification of oligotrophic water bodies in the Xinfengjiang Reservorir.In the large enclosure experiment,the abundance and biomass of phytoplankton increased significantly in all nutrient enriched treatments in the presence or absence of fish.The difference was not remarkable between treatments with fish and treaments without fish.In the nutrient enriched treatments without fish,diatoms and peridinium dominance in biomass at the beginning shifted to diatom dominance,then to Cryptophyta,and finally to Ankyra Fott,which belongs to Chlorophyta.The dominant species had similar alteration in the the treatments with fish,but shifted to Chlorella vulgaris as the dominant species finally.Phytoplankton in the nutrient enriched treatments without fish were mainly composed of species less than 10μm at the beginning,and were dominated by those species larger than 30μm in the last two weeks.However,in the treatments with fish,the phytoplankton species with a size larger than 10μm were decreasing as the experiment going on while the species less than 10μm becoming more dominant and reached peak at the end of the experiment.In the treatments without fish,the abundance and biomass of zooplankton increased remarkablely in all three nutrient enriched levels.However,fish addition only had slight effects on the abundance of zooplankton but decreased their biomass significantly. In the treatments without fish,nutrient enrichment remarkably enhanced both abundance and biomass of Phyllodiaptornus tunguidus and Daphnia geleata,but silver carp decreased the abundance and biomass of cladocerans,especially Daphnia geleata.There was no significant effect on Phyllodiaptomus tunguidus.Abundance of rotifers did not show significant changes within the nutrient enrichments,but increased in the treatments with fish.In control treatments,the dominant species shifted from Daphnia geleata to Phyllodiaptomus tunguidus and its copepodites.These results indicate that Daphnia could become the dominant species in water body without fish or with low fish biomass in the tropics and subtropics.Filter-feeding fish does not decrease the effect of trophic cascade effect during eutrophication of freshwater in these regions. Therefore,the ecological effects of filter-feeding fish in tropical oligo- and mesotrohic water bodies should be paid enough attention for ecosystem management.更多还原