1. Fish assemblages in estuaries have a much lower species richness (number of taxa) when compared with the combined numbers of freshwater and marine species from adjacent aquatic ecosystems. This is primarily because of the relatively harsh and fluctuating physico‐chemical conditions in estuaries compared with the more stable freshwater and marine environments.
2. A comprehensive fish survey of estuaries in South Africa is used as a basis to determine fish species richness in subtropical, warm temperate, and cool temperate systems along the coast, and to assess the degree of redundancy in the different biogeographic regions.
3. In general, only one or two species belonging to each of the detritivorous, piscivorous, zoobenthivorous, and zooplanktivorous fish guilds are numerically well represented in the larger cool temperate estuaries, but between four and 10 species in each of these guilds are usually recorded in the larger subtropical estuaries.
4. Although the overall low redundancy of fish species groups in estuaries has already been formally recognized in the literature, this short note highlights the sensitivity of certain trophic guilds in temperate South African estuaries to any form of redundancy, a characteristic that may be equally applicable, based on declining species richness with increasing latitude, to temperate estuaries in other parts of the world.

中文翻译：

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河口鱼类物种冗余：全球变化压力下温带河口的主要保护问题

1. 与来自相邻水生生态系统的淡水和海洋物种的总数相比，河口鱼类种群的物种丰富度（分类单元数）要低得多。这主要是由于与较稳定的淡水和海洋环境相比，河口的理化条件相对苛刻和多变。
2. 南非对河口进行了全面的鱼类调查，以此为基础确定沿海亚热带，温带和凉带温带系统中鱼类的丰富度，并评估了不同生物地理区域的冗余程度。
3. 一般而言，在较大的凉爽温带河口中，只有一种或两种属于每个有害的，食鱼性的，食肉性的和游动性的鱼类行会在数字上得到很好的代表，但是在这些行会中通常每个行会记录到4至10种。较大的亚热带河口。
4. 尽管文献中已经正式认识到河口鱼类物种群体总体上的低冗余度，但本简短注释强调了温带南非河口某些营养协会对任何形式的冗余度的敏感性，这一特征可能同样适用，基于随着纬度的增加，物种丰富度不断下降，以温和世界其他地区的河口。