Kennedy C R
Department of Biological Sciences, Hatherly Laboratories, University of Exeter, U.K.
Parassitologia. 1997 Sep;39(3):249-54.
The use of free-living invertebrates as indicators of freshwater quality is long established and well documented. The basic approaches employed are 1) recognition of indicator species, 2) recognition of changes, usually reduction, in community diversity and 3) construction of biological indices, combining knowledge of 1) and/or 2) and taking into account changes in species abundance. These approaches employ invertebrates because of their immobility and longevity, and rely on a detailed body of ecological knowledge so that biotic changes can be related clearly to particular environmental changes. If we are to use parasites in the same way, we must show that pollution does affect parasites and then ask whether they can serve as indicator species, and whether changes in parasite communities can serve as indicators of specific changes in environmental conditions. We must also ask if parasites are better indicators than free living organisms. Parasites also pose additional difficulties: they are mobile because their fish hosts are, and the effects of pollution may be direct on the parasite or indirect on any of its hosts or act via host immune systems. No species has evolved and adapted to pollution, and presence or absence of a parasite species or changes in community may have many causes. Both presence and community structure vary considerably between localities and over time within localities and we cannot yet relate these changes to particular causes. We can record changes and differences, but with present lack of knowledge cannot relate them unequivocally to specific causal factors or environmental changes. Use of parasites as bio-accumulators shows promise, as does monitoring of a locality over time, but one-off surveys are of no use. Until we are prepared to stand up in a court of law and be cross-examined on our statement that these parasites clearly show a particular change in the environment, the answer to both questions above must be no.
将自由生活的无脊椎动物用作淡水水质指标的做法由来已久且有充分记录。所采用的基本方法有：1）识别指示物种；2）识别群落多样性的变化，通常是减少；3）构建生物指数，综合1）和/或2）的知识并考虑物种丰度的变化。采用这些方法是因为无脊椎动物具有不移动和寿命长的特点，并且依赖于详细的生态学知识，以便生物变化能够与特定的环境变化明确相关。如果我们要以同样的方式使用寄生虫，我们必须证明污染确实会影响寄生虫，然后询问它们是否可以作为指示物种，以及寄生虫群落的变化是否可以作为环境条件特定变化的指标。我们还必须询问寄生虫是否比自由生活的生物是更好的指标。寄生虫还带来了额外的困难：它们会移动是因为其鱼类宿主会移动，污染的影响可能直接作用于寄生虫，或间接作用于其任何宿主，或通过宿主免疫系统起作用。没有物种是为适应污染而进化的，寄生虫物种的存在或缺失或群落变化可能有多种原因。寄生虫的存在和群落结构在不同地点之间以及在同一地点的不同时间内都有很大差异，我们尚无法将这些变化与特定原因联系起来。我们可以记录变化和差异，但由于目前缺乏知识，无法明确将它们与特定的因果因素或环境变化联系起来。将寄生虫用作生物累积器显示出前景，对一个地点进行长期监测也是如此，但一次性调查毫无用处。除非我们准备好在法庭上站起来，并就我们声称这些寄生虫清楚地表明环境发生了特定变化的陈述接受盘问，否则上述两个问题的答案都必须是否定的。
