莫拉克颱風過後臺灣災區淡水蟹類及棲地之時序變化趨勢

Trends of Freshwater Crabs and Habitats in Southern Taiwan after Typhoon Morakot

經由數十年森林火災相關研究瞭解，偶發性大天災常造成生態系於不同時空尺度的重大影響。但於現今全球暖化與氣候變遷影響加速下，卻少有研究探討漸趨惡化的颱風天災與淡水域生態系間相關效應，而特別針對最可能遭受颱風侵襲而喪失重要生物多樣性資源的淡水蟹類，至今仍無相關研究。臺灣於2009年8月遭遇莫拉克颱風襲擊，造成臺灣歷史上最嚴重的水患、土石流及山崩災情。本研究即於莫拉克颱風過後，運用系統性取樣22處災區研究樣站，除於2010年1月風災後初期調查淡水蟹類的基線資料外，並自2011年春季至2013年夏季期間每季持續進行調查淡水蟹類個體及群聚的6項相關指標（體型、性別、成熟、群聚生物多樣性、群聚豐富度及群聚生物量），用以分析其於風災後的時序變化趨勢。研究結果發現淡水蟹類群聚豐富度顯著上升與群聚生物量近顯著增加的趨勢，顯示風災後的淡水蟹類數量與其棲地資源正在恢復，另經由時間序列分析發現，受限於緩慢增加的群聚生物量與快速上升的群聚豐富度，造成淡水蟹類體型小型化的附帶效應。我們推測在極具破壞性的天災發生後，如同莫拉克颱風所造成的巨大災難，淡水蟹類可快速增加個體數量，主動調整適應策略朝向r型選汰生活史模式，藉以提高其子代於更趨劇烈變化環境中的存活機率。

Natural disasters can cause severe influences on the ecosystem through different spatial and temporal scales. Decades of forest fire researches have been conducted to understand the effects of natural disaster on the ecosystem. However, the effects of typhoon upon freshwater ecosystem remain unclear, and the difficulty is exacerbated by the impacts of global warming and climate change. Furthermore, freshwater crabs are perhaps in a much difficult situation because their most important biodiversity occurs in locations where the most destructive typhoons happen, but there is still no research focusing on it. Typhoon Morakot passed through Taiwan in August 2009, and the heavy rainfall brought by the typhoon resulted in serious floods, debris flows and landslides in southern Taiwan. From spring 2010 to summer 2013, we investigated the trends of freshwater crabs and their habitats after Typhoon Morakot using systematic sampling and analyzing methods for six individual and community indicators (body size, sex, maturity, community biodiversity, community abundance and community biomass). Our results revealed highly increasing community abundance and marginally increasing community biomass in freshwater crabs, which indicated that the numbers of freshwater crabs and their habitat resources were recovering after typhoon. Interestingly, the constraints of gradually ascending community biomass and drastically rising community abundance resulted in the ”side-effect” of body size decline in freshwater crabs. To reduce extinction risks in a dramatically fluctuating environment, we surmise that freshwater crabs shift their adaptive strategy toward r-selected life history to benefit their reproductive success in face of extreme catastrophes like Typhoon Morakot.