都市化對河口域仔稚魚群集構造的影響：以北台灣公司田溪為例

Abstract

河口域具有極高的生產力，是魚類及其他生物的重要棲地、覓食地和哺育場。隨著都市化進程愈加快速和廣泛的發生，大規模的城市開發不僅造成地景變化，同時干擾河川生態，居於此地的生物也隨之受到影響。淡海新市鎮開發項目動工後，位於其南側的公司田溪沿岸及河口域發生了明顯的地景改變。為了瞭解此開發項目與公司田溪河口域仔稚魚群集構造變化的相關性，選取工程第一開發區開發前1984-1985年，開發中1997-1998年和開發後2004-2005年公司田溪河口域之仔稚魚魚類調查資料，分析比較其豐富度、多樣性指數和物種組成的時間變化，並按不同棲性同功群類型分類以觀察不同棲性仔稚魚比例季節間變化，以及比例結構是否隨時間變化。同時，使用人工辨識方法處理開發前後不同時期的衛星影像，比較都市化面積的改變。綜合以上兩個結果，加以相關文獻回顧，期望推測得到淡海新市鎮開發與公司田溪仔稚魚群集構造改變之相關性。 衛星影像結果顯示淡海新市鎮工程開發自1994年起都市化面積逐漸增長；填海造陸工程於1995-2001間完成，陸上建物以及道路的修建主要在1997年之後開始。三個年度仔稚魚調查所得個體數分別為6802尾/小時、15467尾/小時和3041尾/小時。物種數隨季節變化，春季增加，夏季後減少，但魚種(及科別)的數目從1984-1985的86種(40科)減少至1997-1998年95種(49科)至2004-2005年的39種(21科)，群集總體豐富度和多樣性損失頗高。物種組成在三個年度有很大差異，且群集中魚類的優勢棲性同功群類型由沿岸河口型轉變為沙泥型和河海洄游型。 群集豐富度及多樣性的總體降低體現出公司田溪河口域生態逐漸惡化而轉變為不利於魚類棲息的環境。很多因素可能是導致這種衰落的原因，本研究分析結果得到魚類棲性同功群優勢類型轉變，故推測原因為淡海新市鎮陸地開發、填海造陸以及河道改造工程等都市化行為已帶來足夠規模的干擾，改變了原本自然且適合仔稚魚棲息的河口和河岸，為公司田溪河口仔稚魚群集變化提供機會。

Estuaries own high productivity, and function as critical habitat, foraging site and nursery ground for fishes and other creatures. Many changes have taken place to the estuary landscape due to urbanization, thus bring disturbance to the rivers and the local living creatures. The Danhai New Town Project, a government permitted urban development, started in 1994. Since then, many changes to the landscape have been witnessed in the nearby estuary of Gongsitian Stream. To understand the correlation between the urbanization project and the assemblage structure of estuary fish larvae and juveniles in the estuary, species richness, diversity and composition of estuary fish larvae and juveniles were compared during the period in 1984-1985, 1997-1998 and 2004-2005. Species are divided into different habitat functional guild; seasonal changes of the proportion of different guilds are compared in and between these years. Besides, we compared satellite images of different years to illustrate the changes of urbanization area and present the landscape transformation from natural to artificial before and during the urbanization project. The analysis of the satellite images reflect that the urbanization area gradually increased since 1994, a land reclaiming happened during 1995-2001, and the construction of buildings and roads took place after 1997. The three samplings on fish larvae and juveniles during the 20 years showed similar seasonal pattern, but the total individual number decreased with time (from 6802 to 15467 to 3041, individual/hour). The number of fish species (and families) has a little decrease from 86 species (40 families) in 1984-1985 to 39 species (21 families) in 2004-2005. The species number changes seasonally in all year periods but with a similar trend that increases in spring and falls after summer. The significant differences (p<0.05) of the richness and diversity indexes of the 3 years reflect the total loss on assemblage richness and diversity. A similarity test reveals that the species compositions in the 3 years have little in common, which indicates a phase transition during the 20 years. Six habitat functional guilds of fishes can be found, but the dominant guild changed from estuarine to coastal water fish in 1984-1985 to diadromous and sand-mud fish in 2004-2005. The losses of richness and diversity on the fish larvae and juveniles in Gongsitian Stream estuary reflect a deterioration of the estuary area. There are many reasons could be responsible for the pattern. Based on the transformation of dominant habitat guild, it suggests that the urbanized landscape changes, including land clearing, construction of buildings and roads, land reclamation and stream channel transformation, bring enough disturbances to the natural stream estuary. These changes the fish assemblage in Gongsitian Stream estuary.