【作者】 李承春；

【导师】 徐奎栋； 类彦立；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 海洋生物， 2012， 博士

【摘要】 纤毛虫是各类环境中常见的微型生物类群，一直以来由于其形态的多样性受到广泛的关注。上世纪八十年代“海洋微型食物环”的概念提出以来，纤毛虫在微型生物食物环中的生态作用也逐渐引起了研究的重视。目前对于纤毛虫在浮游微食物网中的作用已有较一致的认识，纤毛虫作为微食物网的顶级捕食者能够有效的摄食控制细菌、微藻、鞭毛虫、较小的纤毛虫等类群，同时作为小型后生动物如桡足类的主要食物，将微食物网的生产力传递到高级经典食物链。因而，纤毛虫被认为是浮游生态系统关键的一环。然而，对于底栖纤毛虫的生态作用却知之甚少。海洋沉积物与水体在理化环境和生物群落构成上有很大不同，微型生物类群的丰度和生物量显著高于浮游环境。纤毛虫在底栖微食物网中可能具有不同于浮游纤毛虫的生态特征。为此，本研究以海洋大型底栖纤毛虫—叶状突口虫(Condylostoma spatiosum)为指标生物，从种群和群落水平上对底栖纤毛虫的生态特征及其对环境因子变化的响应、适应机制进行了探讨。为了解不同单胞藻类投喂和温度下纤毛虫的种群增长，在室内15℃、20℃及25℃下分别投饲等边金藻、牟氏角毛藻、杜氏盐藻和三角褐指藻，进行了叶状突口虫的种群增长研究。结果显示，叶状突口虫的增长率总体上随温度升高而加快，在15℃下的增长率远低于20℃和25℃下。同时，不同食物也对增长率产生了明显影响：杜氏盐藻投喂组的纤毛虫在三种温度下均获得较高的增长率(25℃下达0.692d-1)和最大的种群数量，等边金藻投喂组则在增长率和最大种群数量上均较小，而15℃下牟氏角毛藻投喂组的种群增长率最低(仅0.103d-1)。统计分析显示，食物和温度以及两者的交互作用对叶状突口虫种群增长率均有显著影响(P<0.001)。本研究表明，底栖纤毛虫在较高温度和较佳食物条件下可获得更高的种群增长率。由于底栖纤毛虫的多样性(大小、食性等)及食物因子(类型及品质)的复杂性，以及食物与温度可能存在的交互作用，经由不同温度和食物条件测得的种群增长率，进而估算的纤毛虫生产力可能产生较大差异。由此，在底栖微食物网模型构建时应同时考虑温度和食物的交互影响。为了解叶状突口虫种群增长与摄食功能的对温度和食物浓度的响应，以一种异养腰鞭毛虫—尖尾虫(Oxyrrhis marina)作为饵料投喂叶状突口虫，研究了不同温度和食物浓度下叶状突口虫种群的增长率、细胞体积、生产力、摄食率和增长效率(gross growth efficiency, GGE)，并以常用的双曲线模型拟合上述指标，得到了不同温度下Holling Type II模型的参数。结果发现随着温度升高叶状突口虫种群最大增长率、最大生产力、最大摄食率增大，而最大细胞体积降低。随着温度从12℃增加到24℃，叶状突口虫在饱和食物浓度下的GGE由～45%降低至20%。我们也用多变量非线性模型对数据进行了拟合，得到了叶状突口虫种群增长、细胞体积、生产力及其摄食率关于温度和尖尾虫浓度变化的回归方程。为了解叶状突口虫对海洋沉积物中纤毛虫群落结构的影响，在潮间带进行了原位控制实验。实验的设置包括隔离/不隔离大型捕食者以及在隔离大型捕食者的情况下添加/不添加叶状突口虫。在第1、3、6、10天对各处理取样分析纤毛虫群落结构。结果发现，这两种处理均对纤毛虫群落结构产生差异。在隔离大型捕食者时，总的纤毛虫丰度趋于增加，而总的生物量保持不变。而这一趋势在添加叶状突口虫的处理中被削弱。从生物量来看，异毛纲(Heterotrichea)与叶咽纲(Phyllopharygea)为优势类群。异毛纲的生物量百分比在添加叶状突口虫的处理中由38%降到20%，而在未添加叶状突口虫的处理组和对照组中却基本不变。叶咽纲的生物量百分比在添加叶状突口虫的处理中由27%增加到53%，而在未添加叶状突口虫的处理中前3天降低7天升高。群落相似性分析(ANOSIM)表明添加叶状突口虫使得底栖纤毛虫群落发生了迁移，其中Zosterodasys agamalievi和Tunicothrix brachysticha对处理间群落的非相似性贡献最大。然而，添加纤毛虫与隔离大型捕食者两种处理均未对纤毛虫物种数和多样性产生影响。这一结果与前人的结果一致，即更高营养级的改变对纤毛虫群落影响不大。更多还原

【Abstract】 Ciliate is a group of heterotrophs commonly found both in freshwater and marineenvironments, with high abundance and diversity. Their ecological role in microbialfood web has received a lot of concern since the concept of “micro-loop” was firstdiscussed in1980’s. Ciliate has been recognized as an important nexus of the microbialfood web in pelagic water. On one hand, ciliates could effectively graze on the othermicroorganisms including bacteria, algae, flagellates and small ciliates. On the otherhand, ciliates could be largely grazed by metazoans (e.g. copepods). However, studiesaddressing the ecological role of ciliates in marine benthic environments are very scant.Marine sediments are different from the pelagic water not only in environmental factorsbut also in community structure of biota. Ciliates adapted to these habitats may havedifferent life strategies from the pelagic ones.Condylostoma has been documented as a very large ciliate frequently dominant invarious marine benthic microbial communities, but little is known about the effects oftemperature and food type and concentration on its growth and grazing. To reveal thepopulation dynamics of marine benthic ciliates and to assess the effects of temperatureand food supply on ciliate growth, we investigated the growth of Condylostomaspatiosum, a large and frequently dominant ciliate in intertidal zone. The laboratoryexperiments were conducted at three temperatures of15°C,20°C and25°C andsupplied with four individual algal species (Isochrysis galbana, Chaetoceros mulleri,Dunaliella salina and Phaeodactylum tricornutum) as prey. The growth rates ofCondylostoma spatiosum generally increased with increasing temperature, with those at15°C distinctly lower than at20°C and25°C. Meanwhile, food prey types markedlyaffected the growth rates of C. spatiosum. The growth rates and maximal populationsizes were the highest when supplying with the prey Dunaliella salina, while bothvalues were distinctly low when feeding with Isochrysis galbana, the lowest growthrates occurred at15°C with Chaetoceros mulleri as food prey. Statistical analysissuggested that the effects of temperature and food supply as well as their interactionswere significant (P <0.001). Our study indicates that the growth of benthic ciliatescould be enhanced by higher temperature and appropriate food supply. The diversity of benthic ciliates (e.g. size, feeding type) and the complexity of food supplies (e.g. preytype, quality) as well as the potential interactions between temperature and food supplymay result in deviation of growth rate when the value obtained from individualcircumstances is generalized. It is suggested that temperature and food supply should betaken into account simultaneously in the modeling of benthic microbial food webMeanwhile, using the heterotrophic dinoflagellate Oxyrrhis marina as prey, wedetermined the specific growth rate, cell volume, specific production and ingestion rateof Condylostoma spatiosum at different temperatures and prey concentrations. Thesegrowth and grazing parameters typically followed a hyperbolic response to preyconcentration. By applying iterative curve-fitting to the data at each temperature, wefound that, with increasing temperature, the maximum specific growth rate, maximumspecific production and maximum ingestion rate of C. spatiosum generally increased,while the maximum cell volume decreased. The gross growth efficiency of C. spatiosumgenerally decreased at saturated prey concentration from about45%to25%as thetemperature increased from12to24C. By fitting these data iteratively to multi-variablenonlinear models, we obtained predictive equations for the growth rate, cell volume andingestion rate with respect to temperature and prey concentration.In situ experiments were also conducted to investigate the potential effects ofCondylostoma spatiosum, a large-sized ciliate frequently dominated in various marinebenthic habitats, on benthic ciliate community in an intertidal flat. The manipulationsincluded the presence/absence of macro grazers and addition of C. spatiosum in theabsence of macro grazers. Ciliates responded to both manipulations of macro grazersand C. spatiosum. Total ciliate abundance tended to increase in the absence of macrograzers, while total ciliate biomass was remarkably constant. But this trend was likelyweakened by addition of C. spatiosum. Heterotrichea and Phyllopharyngea dominatedthe ciliate community in terms of biomass. Biomass percentage of Heterotricheadecreased from38%of total ciliate biomass to20%in the C. spatiosum added treatment,while it was relatively consistent in no C. spatiosum added treatment and control.Biomass percentage of Phyllopharyngea increased from27%to53%when C.spatiosum was added, while it decreased slightly for the first3days and showed anincrease in the following days in no C. spatiosum added treatment. ANOSIM alsoindicated that addition of C. spatiosum shifted the ciliate community. Zosterodasys agamalievi and Tunicothrix brachysticha generally contributed the most dissimilarity.However, neither tube effect nor addition of C. spatiosum changed the species richnessand diversity. The results are in consistent with previous work that ciliates are lesssensitive to changes at higher level.更多还原