Associations of zooplankton in six crater lakes in Arizona, Mexico and New Mexico

Zooplankton associations in six crater lakes have been compared by means of indices of similarity and diversity, and by k ‐dominance curves. The lakes covered a wide range of salinities and vegetational characteristics. The total number of species identified were: Protozoa, 34; Rotifera, 48; Gastrotricha, 7; Crustacea, 24; and Chaoborus larvae, 2; giving an overall total of 115. The numbers of zooplankton species in each lake varied from 68, in a richly vegetated fresh crater lake in Arizona, to one in a highly saline lake in New Mexico. Testate rhizopods and gastrotrichs were not found in the more saline lakes. A comparison of the rotifer associations with those of crater lakes in other parts of the world shows that there is a general tendency for a reduction in the total number of species when the conductivity rises above 400 μS cm −1 20°C, and when the conductivity reaches 10,000 μS cm −1 20°C the number of rotifer species is usually reduced to two. The two species found at high salinities show some variation in different parts of the world, but generally include species of Brachionus and Hexarthra. There is a general tendency for the number of rotifer species in a crater lake to increase with increasing vegetation, at least up to the stage where there is a dense, zoned vegetation, and before a complete mosaic of vegetation covers the lake.