臺灣小燕鷗(Sternula albifrons)環境重金屬之生物累積與其對巢蛋品質之影響

Abstract

重金屬污染事件頻繁的臺灣，至今仍缺乏河口溼地高營養階層物種的生物累積與毒害影響相關報告。小燕鷗是二級珍貴稀有保育類動物，並有覓食範圍短與高營養階層物種之特性，適合作為河口濕地重金屬的生物監測物種。本研究在臺灣四個主要的小燕鷗繁殖地：宜蘭縣蘭陽溪口水鳥保護區(蘭陽)、宜蘭縣新城溪出海口(新城)、彰化縣彰濱工業區崙尾區(崙尾)、澎湖縣吉貝島(吉貝)，採集幼鳥胸羽與成鳥覓食水域的淺層底泥，檢測重金屬鉛、鎘與汞濃度，並於蘭陽、新城與崙尾調查小燕鷗的巢蛋品質(包含：窩卵數、巢蛋體積與蛋殼厚度)。四個樣區的小燕鷗幼鳥胸羽，與底泥鉛及鎘濃度皆呈顯著正相關(p<0.001)，顯示累積於底泥的鉛與鎘可能藉由食物鏈進入小燕鷗幼鳥體內，此外蘭陽與新城樣區的幼鳥胸羽鉛與鎘濃度(4.46 ppm, 2.69 ppm; 5.02 ppm, 3.04 ppm)，高於前人認為可能對海鳥造成負面影響的濃度(4 ppm, 2 ppm)。三個樣區的底泥鉛、鎘及汞濃度與蛋殼厚度皆呈顯著負相關(p<0.001)，並於重金屬濃度最高的新城樣區，觀察到小燕鷗的窩卵數與巢蛋體積較小，且蛋殼較薄，顯示高重金屬濃度對小燕鷗的巢蛋品質具有負面影響。在底泥重金屬偏高的樣區，小燕鷗雌鳥可能因攝食重金屬濃度較高的魚類，導致體內鈣質調控失衡，而產生品質較差的巢蛋，因此未來應追縱繁殖地的重金屬來源並設法減量，以降低小燕鷗受重金屬毒害影響之風險。然而，重金屬對生態系造成的影響並非只有小燕鷗，至今臺灣關於重金屬在各個營養階層的累積濃度，與毒害影響之相關研究仍十分缺乏，因此，臺灣急需進行生態系單一物種不同時期、多種物種與大尺度的重金屬研究。

Annually, Taiwan is seriously affected by heavy metal pollution. However, very little research is being done on heavy metal bioaccumulation and the toxic effects on higher trophic level creatures such as seabirds in Taiwan’s marine and coastal areas. The Little Tern, classified as a rare and valuable species, is a high trophic level predator with a short foraging range in Taiwan. These characteristics make Little Terns a suitable species to investigate the effects of heavy metals in Taiwan’s marine and coastal areas. In this study, four main breeding sites were chosen: Lanyang river estuary (Lanyang) and Xincheng river estuary (Xincheng) in Yilan county, Lunwei Industrial Park (Lunwei) in Changhua county, and Jibei island (Jibei) in Penghu County. Feathers of nestlings and the sediments in their foraging area were collected from each site for analysis on lead, cadmium, and mercury concentrations. In addition, the clutch size, egg volume, and eggshell thickness were recorded from Lanyang, Xincheng, and Lunwei. Lead and cadmium concentrations in the feathers collected were consistent with the sediment concentrations (p<0.001), which suggests that lead and cadmium in sediments pass through the food chain, then accumulate in feathers. In addition, lead and cadmium in nestling feathers from Lanyang and Xincheng (4.46 ppm, 2.69 ppm; 5.02 ppm, 3.04 ppm) were above the effects level (4 ppm, 2 ppm). This high concentration of heavy metals may cause negative chronic effects in seabird. In Xincheng, the site with the highest metal concentration, the average clutch size was reduced as was the egg volume and shell thickness. For conservation purposes, metal levels in breeding sites should be minimized to reduce the risk of heavy metal toxicity, and monitoring of the heavy metal sources is necessary. In addition, bioaccumulation and toxic effects on single or multiple species is imperative for future research.