Kainz Martin, Arts Michael T, Mazumder Asit
Aquatic Ecosystem Management Research Division, National Water Research Institute, Environment Canada, 867 Lakeshore Road, P.O. Box 505, Burlington, ON L7R 4A6, Canada.
Environ Pollut. 2008 Sep;155(2):262-70. doi: 10.1016/j.envpol.2007.11.021. Epub 2007 Dec 31.
We investigated seasonal variability of essential fatty acids (EFA) and methyl mercury (MeHg) concentrations in four size categories of planktonic organisms in two coastal lakes. MeHg concentrations increased significantly with increasing plankton size and were independent of plankton taxonomy. However, total EFA increased from seston to mesozooplankton, but decreased in the cladoceran-dominated macrozooplankton size-class. Analysis of EFA patterns revealed that linoleic, alpha-linolenic, arachidonic, and eicosapentaenoic acids increased with increasing zooplankton size, but docosahexaenoic acid (DHA) in the cladoceran-dominated macrozooplankton was generally lower than in seston. This consistent pattern demonstrates that cladocerans, although bioaccumulating MeHg, convey less DHA than similar-sized copepods to their consumers. It is thus evident that fish consuming cladocerans have restricted access to DHA, yet unrestricted dietary access to MeHg. Thus, the structure of planktonic food webs clearly affects the composition of EFA and regulates dietary supply of these essential nutrients, while MeHg bioaccumulates with increasing zooplankton size.
我们研究了两个沿海湖泊中四类浮游生物体内必需脂肪酸（EFA）和甲基汞（MeHg）浓度的季节变化。甲基汞浓度随浮游生物大小的增加而显著升高，且与浮游生物的分类无关。然而，总必需脂肪酸从悬浮微粒增加到中型浮游生物，但在以枝角类为主的大型浮游生物类别中有所下降。对必需脂肪酸模式的分析表明，亚油酸、α-亚麻酸、花生四烯酸和二十碳五烯酸随浮游动物大小的增加而增加，但以枝角类为主的大型浮游生物中的二十二碳六烯酸（DHA）通常低于悬浮微粒中的含量。这种一致的模式表明，枝角类虽然会生物累积甲基汞，但其向消费者传递的DHA比同等大小的桡足类少。因此，显然以枝角类为食的鱼类获取DHA的途径有限，但摄入甲基汞的饮食途径不受限制。因此，浮游食物网的结构明显影响必需脂肪酸的组成，并调节这些必需营养素的饮食供应，而甲基汞则随着浮游动物大小的增加而生物累积。
