臺灣海峽北部撓腳類與仔稚魚群集組成受水文因數之影響

Abstract

本研究之目的為探討北部臺灣海峽中橈腳類和仔稚魚的物種組成、豐度和分佈對應於水文環境的時空變動。臺灣海峽的水文環境主要受到中國沿岸流、南海表層水以及黑潮支流在不同季節間相互推移，加上地形效應以及源自大陸和台灣的河流沖淡水所調控。從水文資料的分析中我們看到了季節性以及空間性的變異，定義了8個水團，包括夏季：海峽西側水、海峽東側水、東海水；冬季：海峽西側水、海峽東側水、東海水；春季：大陸沿岸水和黑潮水。以橈腳類的物種組成進行對應分析的結果，測站間的社群區分大體上與水文分析中定義的水團一致。以降趨對應分析和K均值分析也得到類似的結果。以仔稚魚物種組成進行對應分析的結果與水團對應不明顯。以降趨對應分析得到的社群區分可以看到季節變異但沒有明顯的空間變異，而K均值分析也得到類似的結果。優勢物種分析也顯示了時空上的變化。我們以典型對應分析探討這些優勢物種與水文因數的關係。再現群分析顯示一個主要群由橈腳類組成，包括了Acrocalanus gibber、Canthocalanus pauper、Euterpina acutifrons、Oithona attenuata、Oithona plumifera、Oncaea conifera、Oncaea venusta、Paracalanus pavus、Parvocalanus crossirostris、Temora turbinata，有兩個仔稚魚物種Benthosema pterotum、Trichiurus lepturus會與橈腳類構成次群，也表示了橈腳類與仔稚魚之間的關係。 由物種豐度以及歧異度的分佈情形可以看出，在夏、冬季節有從大陸沿岸往大洋方向遞增的趨勢；春季時，受黑潮影響的區域高於受大陸沿岸水影響的區域。指標種分析顯示了季節性的變化。生物豐度也有季節性變化，以橈腳類而言，夏季＞春季＞冬季；以仔稚魚而言，夏季＞冬季，但夏季與春季無顯著差異，春季與冬季無顯著差異。迴歸分析仔稚魚密度與橈腳類密度成正相關。

This study analyzed the spatial and temporal variation of copepods and larval fishes in relation to the hydrographic conditions of northern Taiwan Strait. The hydrographic conditions are influenced by three main currents, China coastal current, South China Sea warm current and Kuroshio branch current, as well as the topographic effect in the Strait. The river runoffs from the China mainland and Taiwan island also have immense impact. According to the hydrographic data, we defined 8 ecological zones showing seasonal and spatial variations, including summer: western Taiwan Strait, eastern Taiwan Strait, East China Sea; winter: western Taiwan Strait, eastern Taiwan Strait, East China Sea; spring: China coastal current region and Kuroshio branch region. Correspondence analysis based on copepod composition resulted in station associations, which are generally consistent with these ecological zonations. Detrend correspondence analysis and K-means classification also show the similar results. The result of correspondence analysis based on larval fish composition shows no clear zonations. Detrend correspondence analysis resulted in station associations, which shows clear seasonal variation but not spatial zonations, and the result of K-means classification was similar to that of detrend correspondence analysis. Dominant species analysis also validated the seasonal and spatial variations of copepods and larval fishes. Species associations of dominant species of copepods and larval fishes, and the relationship between these species and hydrographic factors were constructed through canonical correspondence analysis. Two-way indicator species analysis provided insightful information concerning the spatial and temporal distribution of dominant species. Recurrent group analysis showed a main concurrent group consisted of copepod species and the relationship between copepod and larval fish species. Analysis on the species richness and diversity revealed that these indices increase from the China costal side to the offshore side in summer and winter and are higher in the area affected by Kuroshio than that affected by China coastal current in spring. Indicator species of copepods and larval fishes of each season were extracted through indicator species analysis. Abundance of copepods and larval fishes also showed seasonal variation. Of copepods, abundance is lower in spring than summer, and least in winter. Of larval fishes, abundance is higher in summer than winter, but no difference exists between summer and spring and between spring and winter. The larval fish abundance is positively related with copepod abundance.