Meiofaunal organisms are the predominant metazoans in benthic systems and important members of the benthic food web. They are defined by mesh size and specifically by their retention on a sieve with a 44-µm mesh size. In this study, we examined the accuracy of this standard collection method by counting the number of meiobenthic individuals, life stages and nematode species in a sample. A filter cascade consisting of five different mesh sizes (41 µm, 30 µm, 20 µm, 10 µm and 1 µm) was used to fractionate a natural freshwater meiobenthic collection, and the individuals in each fraction were then counted. In line with the current definition of meiofauna, all tardigrades, microcrustaceans, chironomids and oligochaetes were retained by the largest mesh size, whereas 9% of the rotifers were first retained on the 30-µm meshes. For nematodes, 23% were not retained on the 41-µm meshes and individuals were collected even from the 1-µm fraction. With declining mesh size, the yield of retained nematodes increased, the age structure shifted to juveniles, evenness declined, and the species composition changed. As all of these findings were significant, this study therefore shows that the current definition of meiofauna is not sufficient to encompass the entire spectrum of meiofauna present in a sample and may result in misleading assessments of the diversity and composition of these organisms. We therefore propose that, especially for nematodes, a definition based on a smaller mesh size (at least 20 µm) is more appropriate.

藻类生物是底栖系统中的主要后生动物，是底栖食物网的重要成员。它们是由筛孔尺寸定义的，特别是由它们在筛孔尺寸为44 µm的筛子上的保留力定义的。在这项研究中，我们通过计算样品中中底栖个体的数量，生命阶段和线虫种类，检查了此标准收集方法的准确性。使用由五种不同的筛网尺寸（41 µm，30 µm，20 µm，10 µm和1 µm）组成的过滤器级联来分离天然的淡水贝类底物，然后对每个部分的个体进行计数。根据目前对meiofauna的定义，所有的节肢动物，微甲壳类动物，尺虫和寡毛类动物都保留了最大的网眼尺寸，而9％的轮虫首先被保留在30 µm的网眼上。对于线虫，23％的样品没有保留在41 µm的筛网上，甚至从1 µm的样品中也收集了个体。随着网眼尺寸的减小，保留的线虫的产量增加，年龄结构转变为幼虫，均匀度下降，物种组成发生变化。由于所有这些发现都是有意义的，因此，这项研究表明，对meiofauna的当前定义不足以涵盖样品中meiofauna的整个光谱，并且可能导致对这些生物的多样性和组成的误导性评估。因此，我们建议，特别是对于线虫，基于较小的筛孔尺寸（至少20 µm）的定义更为合适。年龄结构转变为少年，均匀度下降，物种组成发生变化。由于所有这些发现都是有意义的，因此，本研究表明，对meiofauna的当前定义不足以涵盖样品中meiofauna的整个光谱，并且可能导致对这些生物的多样性和组成的误导性评估。因此，我们建议，特别是对于线虫，基于较小的筛孔尺寸（至少20 µm）的定义更为合适。年龄结构转变为少年，均匀度下降，物种组成发生变化。由于所有这些发现都是有意义的，因此，本研究表明，对meiofauna的当前定义不足以涵盖样品中meiofauna的整个光谱，并且可能导致对这些生物多样性和组成的误导性评估。因此，我们建议，特别是对于线虫，基于较小的筛孔尺寸（至少20 µm）的定义更为合适。因此，这项研究表明，meiofauna的当前定义不足以涵盖样品中存在的meiofauna的整个光谱，并且可能导致对这些生物的多样性和组成的误导性评估。因此，我们建议，特别是对于线虫，基于较小的筛孔尺寸（至少20 µm）的定义更为合适。因此，这项研究表明，meiofauna的当前定义不足以涵盖样品中存在的meiofauna的整个光谱，并且可能导致对这些生物的多样性和组成的误导性评估。因此，我们建议，特别是对于线虫，基于较小的筛孔尺寸（至少20 µm）的定义更为合适。