淡水河紅樹林林緣擴縮對蟹類群集的影響

Effect of mangrove change on the crab assemblages at Tamsui estuary in Taiwan

盧致穎(Chih-Ying Lu)

指導教授 ： 李培芬

國立臺灣大學/生命科學院/生態學與演化生物學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.01133

摘要

淡水河口溼地包括挖仔尾、竹圍 (淡水河紅樹林)與關渡自然保留區，屬於潮間帶灘地生態系，其所孕育的豐富生物為台灣重要的生態資源。蟹類在灘地生態系中扮演許多重要的角色，如促進養分在食物網中的流轉等。蟹類的群集結構可做為評估環境狀態的指標，而不同族群的分布變化影響了群集的結構，因此了解蟹類族群的分布變遷，可為溼地經營管理提供重要的資訊。灘地蟹類的分布情形會受到許多環境因子的影響，例如底質特徵及紅樹林分布等。水筆仔 (Kandelia obovate)引進淡水河口溼地已有九十年以上歷史，為該地區的優勢物種，其覆蓋範圍至今仍持續地在擴張中。目前關於紅樹林變遷對蟹類的影響缺乏較長時間尺度的研究，本研究藉重複郭 (2001)之實驗方法，於挖仔尾、竹圍及關渡自然保留區進行穿越線調查。比較三樣區在2001年及2014年五種蟹類分布及密度的改變，以及比較紅樹林與紅樹林外開闊灘地間的蟹類多樣性差異，主要目的為探討紅樹林變遷對蟹類群聚可能造成的影響，並分析河水鹽度是否與蟹類密度有線性相關。
三樣區共九條穿越線的調查結果顯示，紅樹林在4條穿越線擴張，5條穿越線消退。於紅樹林擴張樣區，紅樹林蟹類的分布範圍增加，開闊灘地蟹類的分布範圍減少。於紅樹林消退樣區，紅樹林蟹類的分布範圍減少，開闊灘地蟹類的分布變化趨勢不一致，底質變化可能才是影響其分布的主因。擴張紅樹林外開闊灘地的蟹類多樣性低於消退紅樹林外開闊灘地。蟹類密度與鹽度間無顯著的線性相關。
本研究顯示紅樹林的擴張對開闊灘地蟹類可能有負面影響，包括造成分布範圍減少以及較低的多樣性。近年來由於氣候變遷，紅樹林的分布北界可能擴張至更高緯度地區。而目前國內推廣紅樹林栽植，但未進行妥善評估的結果，往往造成需要再以疏伐等方式控制紅樹林擴張。本研究提供了一個紅樹林分布動態變化如何影響灘地蟹類群集的例子，作為往後於灘地進行紅樹林栽植前的評估參考。

關鍵字

族群分布 ； 紅樹林 ； 蟹類群集 ； 河口灘地

並列摘要

Tamsui estuary includes Wazihwei, Chuwei (Tamsui River Mangrove) and Guandu Nature Reserves are tidal mudflat ecosystem. With so many creatures living inside of it, Tamsui estuary is one of the most valuable ecological resources of Taiwan. Crab plays an important role in mudflat ecosystem, such as facilitating the nutrient transfer in a food web. Species distribution changes may affect the assemblage structure, which could be an indicator of habitat status. Therefore the information on how the crab assemblage changes could be useful in mudflat management. Crab species distribution on the tidal mudflat is affected by many environmental factors, such as sediment parameters and mangrove coverage. In Taiwan, mangrove species, Kandelia obovate, has introduced to Tamsui more than ninety years and has become the dominant plant species in this area. Recent research shows that it is still expanding. This study repeats the method done by Kuo (2001), and assesses how the crab species distribution and density changes between 2001 and 2014 in Wazihwei, Chuwei (Tamsui River Mangrove) and Guandu Nature Reserves. The goal is to understand how the mangrove change affects crab distribution, and the difference between mangrove and open mudflat. This study also analyzes the information collected to see if there is a linear correlation between crab density and salinity.
The result of nine transects survey shows that mangrove coverage expanded in four transects and reduced in the others five transects. At mangrove expanding transects, mangrove crab distribution area increases, while open mudflat crab distribution area reduces. At mangrove reducing transects, mangrove crab distribution area reduces. However, the result of open mudflat crab species are different between transects. It needs to be explained by the sediment parameter change. Mangrove expansion adjacent mudflat has lower crab diversity than mangrove reduction adjacent mudflat. There is no significant linear correlation between crab density and salinity.
This research shows that mangrove expansion may have a negative effect on the open mudflat crab. It reflects in the decreases of distribution area and diversity. Open mudflat crab change at mangrove reduction area needs to be explained by the sediment parameter. It may indicate that after mangrove reduction, sediment changes are the main factor that affects crab distribution area. Recently, due to global climate change, mangrove may have the access to expand to higher latitude area. Planting mangrove is popularizing in Taiwan, but planting mangrove without appropriate consideration always lead to mangrove removal due to expansion control. This research provides an example of how the dynamics of mangrove coverage affect crab assemblages on tidal mudflats.

並列關鍵字

Population distribution ； Mangrove ； Crab assemblages ； Estuary mudflat

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