紅樹林大型底棲動物與林木特徵關係

Relationships between macrobenthos communities and tree characteristics in mangroves

潘薪合(Sin-He Pan)

指導教授 ： 林幸助

國立中興大學/生命科學院/生命科學系所/碩士(2020年)

摘要

臺灣部分地區的紅樹林呈現擴張且密集的現象，然而紅樹林疏伐與否具有爭議，因此紅樹林的經營管理成為備受探討的議題。大型底棲動物為判斷紅樹林生態系健康狀態的重要指標，故本研究目的為探討不同樹種之紅樹林林木特徵(樹密度、呼吸根密度、基礎面積)與大型底棲動物之關係。本研究地點位於臺灣西岸，北部以水筆仔(Kandelia obovata)為主要樹種的新竹新豐(XF)、苗栗竹南(ZN)，以及臺灣南部主要樹種為海茄苳(Avicennia marina)的嘉義布袋(BD)、臺南北門(BM)，共4個地點。每個地點分成紅樹林和灘地兩個樣區，每季進行一次現地調查，藉以採集林木特徵與環境因子，並量化大型底棲動物群集。研究結果顯示紅樹林存在與否會影響大型底棲動物之密度、生物量和多樣性，且紅樹林之大型底棲動物組成更為穩定。在不同樹種方面，大型底棲動物群集組成於水筆仔與海茄苳紅樹林間有分群，但不同地點之大型底棲動物群集也有明顯差異，其與各地點林木和環境因子之差異有關。環境因子分析指出大型底棲動物群集組成受食物來源所影響。布袋豐富之底棲藻可吸引粟螺科和方格河口螺等小型螺類；北門之小頭蟲科、雙節蟲科與有機質含量關，北門高密度之大型底棲動物也吸引較多掠食者(如紐形動物門)前來覓食。除了食物來源，弓形革囊星蟲與粉泥黏土含量也呈正相關。紅樹林之細根生物量與大型底棲動物密度呈負相關，可能因為密度過高之根系結構不利於大型底棲動物之鑽掘行為。從本研究之大型底棲動物多樣性與優勢度結果推測北門紅樹林最為健康，而北門紅樹林的大型底棲動物密度最高、樹密度最低、呼吸根密度最高。同樹種下，水筆仔之樹密度和基礎面積的增加也會對底內動物密度產生負面影響；海茄苳之呼吸根密度也和底表動物密度呈負相關，且呼吸根密度亦與底內動物生物量呈正相關。本研究結果顯示不同樹種之林木特徵對大型底棲動物產生不同之影響。本研究發現紅樹林之林木特徵會影響大型底棲動物群集。因此，未來對於紅樹林經營管理之探討(如是否疏伐紅樹林)應納入紅樹林的樹密度、呼吸根密度以及基礎面積等林木特徵。

關鍵字

水筆仔 ； 海茄苳 ； 大型底棲動物 ； 樹密度 ； 群集組成

並列摘要

The mangroves in some locations of Taiwan are now overexpanding. However, mangrove thinning is a controversial problem. Since macrobenthos are regarded as ecological indicators in mangroves, the purpose of this study was to understand the relationships between the density and basal area of mangroves, the density of pneumatophores, and macrobenthos. Four study locations on the western coast of Taiwan were chosen, including Xinfeng (XF) and Zhunan (ZN) in northern Taiwan, which were both dominant by Kandelia obovata, and Budai (BD) and Beimen (BM) in southern Taiwan, which were both dominant by Avicennia marina, were chosen. Each study location was divided into two habitats, mangroves and mudflats. Mangrove and environmental characteristics were determined, and macrobenthic communities were qualified. The results showed that the presence of mangroves can affect the density, biomass and diversity of macrobenthos, and the macrobenthic communities in mangroves was relatively more stable. For different tree species, the macrobenthic communities were different between the mangroves of K. obovata and A. marina, and the macrobenthic communities were also different among four locations. This may be due to the differences in tree characteristics and environmental factors. Aanlyses of environmental factors indicate that the macrobenthic communities were mainly influenced by food sources. For example, the rich benthic microalgae in BD can attract small snails such as Stenothyridae and Iravadia quadrasi. In BM, Capitellidae and Ampharetidae were related to the high organic matter content, and the high density of macrobenthos also attracted more predators (eg. Nemertina) to forage. Besides the food sources, the density of Phascolosoma arcuatum correlated positively with sediment silt/clay content. There was a significantly negative relationship between the biomass of fine roots and the density of macrobenthos, possibly because it might be a barrier for the burrowing of macrobenthos. From the results of macrobenthic diversity and dominance in this study, it is inferred that BM are the healthiest mangrove ecosystem in four sites. In BM, mangroves have the highest density of macrobenthos, lowest tree density, and highest density of the pneumatophores. For the same species of mangroves, the tree density and basal area of K. obovata correlated negatively with the density of infauna. The density of pneumatophores of A. marina correlated negatively and positively correlated with the density of epifauna and the biomass of infauna, respectively. Overall, this study shows that different tree species of mangroves have different effects on the macrobenthic community, and the community of macrobenthos was effected by the mangrove tree characteristics. This study suggests that the management of mangroves such as mangrove thinning should consider the information about tree density, pneumatophores density, and basal area of mangroves.

並列關鍵字

Kandelia obovata ； Avicennia marina ； Macrobenthos ； Tree density ； Community composition

參考文獻

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