七股潟湖潮間帶底棲多毛類群聚及其與環境因子之關係

Abundance and Species Diversity of Benthic Polychaetes in Relation to Sediment Environmental Variables in the Intertidal Zone of Cigu Lagoon, Taiwan

本研究於2009年1月至10月，在台南七股潟湖地區5個不相連潮間帶，分別設置5個樣區共25樣點，對底棲多毛類的種類組成、群聚結構與棲地環境進行4次採樣研究。調查期間採得的多毛類共748隻，分19科25種，其中以沙蠶科（Nereidae）的腺帶刺沙蠶（Neanthes glandicincta）、錐頭蟲科（Orbiniidae）的尖錐蟲（Scoloplos sp.）、海稚蟲科（Spionidae）的印度海稚蟲（Malacoceros indicus）、小頭蟲科（Capitellidae）的小頭蟲（Capitella sp.）爲主要優勢種，合占總數72.2%。底質環境調查結果顯示，此一區域潮間帶底質特性受到海源與陸源作用交互影響，其中粒徑分布主要受到潮流影響，由南北兩個潮口往潟湖中央區粒徑逐漸變小，各樣區間粒徑分布有顯著差異。與粒徑相關之因子如有機碳、有機氮與含水率等，在各樣區之間也有顯著差異。在空間分布上，位於河流端之樣區受到河川有機質輸入影響，其底棲多毛類之數量與多樣性都最高。在時間分布上，底棲多毛類數量也有顯著的季節性差異，族群總數量在1月處於高峰，往後月份逐漸下降，但小頭蟲數量則有逐季上升的情況。位於七股溪口的七股溪樣站，受到河川陸源因子之顯著影響，其多毛類種類與數量之季節性變動尤爲顯著。根據樣區環境因子相關數據，使用非度量多維尺度（NMDS）及典型相關分析（CCA），可將七股潮間帶區分爲4個類群。結果顯示類群組成與環境因子具有相關性，如大寮外排潮間帶之類群組成主要受鹽度及底質有機質含量影響，七股溪潮間帶類群組成與有機質含量具有關聯性，低豐度、低物種數及低多樣性之龍山潮間帶類群組成則受底質顆粒粒徑影響較大。

Benthic polychaets and sediment data (temperature, conductivity, particle size, and contents of organic matters, total nitrogen, and total organic carbon) were collected seasonally at five stations in the intertidal zone of Cigu Lagoon in Tainan, Taiwan, from January to October 2009. A total of 748 individuals of polychates belonging to 25 species and 19 families were collected. Neanthes glandicincta (Nereidae), Scoloplos sp. (Orbiniidae), Malacoceros indicus (Spionidae), and Capitella sp. (Capitellidae) were dominant, occupying 72.2% of the total number of polychaetes collected. Sediment particle sizes and nutrient contents were apparently influenced by tidal actions and inputs from freshwater runoffs from Cigu River and Dalien Creek. Sediment particles were finest at the stations near convergent center of the lagoon and increased in size with distance toward each of the mouths of the drainages. Total organic carbon, total organic nitrogen and water contents were negatively correlated with particle sizes. Abundance and species diversity of polychaetes were highest at the stations situated at the mouths of the drainages. Also, there was an obvious seasonal cycle in polycheates abundance with a peak density in January. An exception was Capitellidae that showed an opposite trend in the cycle, particularly at the stations near the mouth of Cigu River. Based on the analysis of dissimilarity in species composition and environmental variables using NMDS and CCA techniques, four groups (clusters) of polychaetes communities were identified. The results indicated that abundance and species diversity of the polychaete community in the area near Daliao Creek were influenced by sediment salinity and organic contents, while those in the area near Cigu River were affected only by organic contents. Also, small grain sizes of sediments caused lower the abundance and species diversity in the Longshan intertidal zone.