- 學位論文
新山水庫浮游動物種類的分布及對微囊藻團粒粒徑消長之影響
The Speciation of Zooplankton and Its Effects on the Distribution of Colony Size of Microcystis in Hsin-Shan Reservoir
摘要
河川、湖泊及水庫中，經常發生優養化之現象，其中又以微囊藻(Microcystis)為常見的藻華優勢物種。水庫發生藻華時期，不僅會使淨水成本增加，也會造成許多環境問題。微囊藻因為具有團聚之生理現象，使得藻體能在水中垂直移動，克服光線與營養鹽上下分離之情形，幫助藻團取得生長優勢。而過去研究亦發現自然水體中微囊藻團的粒徑，並非均為單一大小，而是具有某特定之粒徑分布，但目前學術界對於微囊藻如何在水中維持某粒徑分布之機制仍不清楚。 本研究認為浮游動物能透過捕食作用，消耗水體中特定粒徑之微囊藻團數量，進而控制及維持微囊藻團的粒徑分布。並透過設置一高密度浮游動物與藻類共存之環境，探討浮游動物對微囊藻團粒徑消長之影響。結果顯示新山水庫浮游動物不以微囊藻藻團為主要食物來源，多偏好以體積更小的微生物以及有機碎屑為食。觀察結果顯示浮游動物的捕食作用，並非自然水體中微囊藻藻團維持特定粒徑分布之主因。此外，本研究藉由分析大量微囊藻藻團樣本，找出微囊藻團自體分裂之規律，並建立數學模式描述藻團藉由該分裂機制，粒徑分布隨時間在水中的變化情形。模擬結果顯示，透過該分裂行為，微囊藻團粒徑分布能在水體中達到動態平衡，維持一穩定狀態。反映此藻團分裂現象有很大的可能為微囊藻維持粒徑分布的關鍵因素。 本論文同時調查新山水庫2015年7月至2016年6月間，不同時空下浮游動物的數量以及組成種類，並將浮游動物豐度與環境因子做相關性分析。研究成果發現，水庫中浮游動物豐度在垂直分布上有明顯的差異，且浮游動物數量與葉綠素a呈顯著正相關。造成此現象主因為浮游動物追隨食物來源以及躲避天敵掠食的行為。新山水庫在藻類大量生長時期，能間接提供浮游動物生長所需的食物條件，因此在藻類數量較豐富的時間空間裡，浮游動物數量亦較豐富。
並列摘要
Microcystis, one of the most notorious bloom-forming cyanobacteria occurring in freshwaters, is able to form colonial aggregates. Large sizes of colonies are helpful to their vertical migration, nutrient storage, and to defend themselves against predation pressure. Therefore, formation of colonies is believed to be a special ability of Microcysits to dominate over other species of phytoplanktons in the thermally stratified lakes or reservoirs. The previous study in this laboratory also found that the particle size of Microcystis in Hsin-Shan Reservoir is not uniform, but a specific distribution. The mechanism with which Microcystis maintain a specific particle size distribution is not clear. In this study we hypothesize that predation by herbivorous zooplankton can consume a large amount of Microcystis colonies, therefore, control the size distribution of Microcystis. Experiments were conducted with zooplanktons and Microcystis colonies collected from Hsin-Shan Reservoir. The results or the investigation of the variation of size distribution and cell numbers of Microcystis indicated that Microcystis colonies are not consumed as food by zooplankton. Predation is not the main reason for Microcystis to maintain its size distribution. We developed a model to simulate the variation of colonies size distribution by using the real observed patterns of colonial division. The results of the simulation indicate that Microcystis can maintain a specific size distribution. That is to say, Microcystis may preserve a dynamic equilibrium of colonial distribution by following a division pattern we proposed. Investigation of the vertical distributions of the composition and abundance of zooplankton had been performed monthly from July 2015 to June 2016. It was found that zooplankton abundance had positive correlation with the concentration of chlorophyll a. Since zooplanktons did not consume algae, the reason of this phenomenon could be that planktonic small animals closely follow their food sources, which may be dead bodies of algae, organic matters excreted by phytoplanktons or some heterotrophic bacteria in vicinity of the colonies and their concentration, which are all related to the concentration of algae.