龜山島周遭海域底泥線蟲之群落

Abstract

海洋線蟲是海底沉積物當中數量最為豐富的小型底棲動物，他們會參與棲地的養分循環與食物網，作為微生物與大型底棲生物間的能量橋梁。因為海洋線蟲對於環境的變動相當敏感，所以可作為評估生態系統的生物指標。龜山島是一座火山島，龜山島的東南方具有多座淺海熱泉，相對地，龜山島的西方則是具有珊瑚礁生態系。從熱泉區到非熱泉區，龜山島大型底棲生物群落變動已有多份研究探討，然而小型底棲動物則未有調查。因此，本研究在環繞龜山島的6個地點進行不同時間點底泥的採集以探討其海洋線蟲群落。採樣地點包括3個熱泉生態系 (近泉、遠泉與CO2泉)、1個珊瑚礁生態系 (龜尾)、2個過渡地點位於熱泉與珊瑚礁之間 (龜北、龜南)。底泥除了用於線蟲的分離外，還會進行粒徑大小的分析與底泥化學組成的分析。結果顯示，珊瑚礁環境的線蟲豐度會隨著時間變化，於春季與夏季豐度會呈現上升的趨勢。近泉與遠泉的線蟲數量無論時間點都非常少，但CO2泉的春季數量大增，並於夏季稍下降。地點不僅影響線蟲在不同時間點的變動情形，還會影響線蟲的群落組成。底泥的物化性質中底泥粒徑與SO42-、Mg2+、Cl-是顯著造成線蟲群落組成差異的重要環境因子。CO2泉以熱泉相關物種及耐受性強的周遭物種為主要組成；龜北獨有物種比例高，以適應粗顆粒的物種為主；龜尾則以適應細顆粒的物種為主。此外，龜尾、龜南到近遠泉則呈現豐度與組成上的連續性變化。

Free-living marine nematodes are the most abundant meiobenthos in marine sediment. They participate in the nutrient cycle and the food web of the habitat, and serve as an energy bridge between macrobenthos and microorganisms. Because free-living marine nematodes are sensitive to environmental variations, they can be served as bioindicators to assess ecosystems. Turtle Island is a volcanic island, the southeastern of the island locates clusters of hydrothermal vents. By contrast, the western has no vent and contains a coral reef ecosystem. Several studies have investigated the composition of macrobenthos around hydrothermal vents of Turtle Island, but there is no survey about meiobenthos. Therefore, we collected sediment samples from 6 sampling sites surrounding Turtle Island each season for a year to investigate the free-living marine nematode communities. The sampling sites included 3 vent sites (Near vent, Far vent, and CO2 vent), 1 coral reef ecosystem (Tail), and 2 buffer sites, between the vent sites and the coral reef (North and South). In addition to the extraction of nematodes, the sediment samples were also analyzed for grain size distribution and chemical ion composition. The results showed that the abundance of nematodes in the coral reef changed over time, with an increasing trend in spring and summer. The number of nematodes in Near vent and Far vent was quite low no matter the time point, but the number of nematodes in CO2 vent increased greatly in spring and decreased slightly in summer. Sampling sites affected not only the temporal variation of the nematode abundance, but also had an impact on the nematode composition. Among the physical and chemical properties of sediment, grain size, SO42-, Mg2+, and Cl- were crucial environmental factors that significantly caused differences in the composition of nematode communities. CO2 vent were mainly composed of vent-related species and surrounding species with strong tolerance. North had own special community, mainly species adapted to very coarse sand. Tail was dominated by species adapted to medium sand. Furthermore, Tail, South, Far vent, and Near vent showed a continuum of changes in the nematode abundance and composition.