The relation of Gammarus zaddachi Sexton to some other species of Gammarus occurring in fresh, estuarine and marine waters

Abstract

Gammarus zaddachi is perhaps the most prolific and widespread of all the estuarine amphipods known to occur in northern Europe, and inhabiting, as it does, the low-salinity estuarine zone and adjacent coasts, it has come to be recognized in recent ecological work as a ‘salinity indicator’.Unfortunately, there has been constant confusion with the other common species of Gammarus, G. locusta, pulex, and duebeni, which has been greatly complicated by the difference in the appearance of zaddachi according as it lives in a freshwater or a saline habitat. It is shown that this difference is entirely due to the sensory equipment, the greater production of hairs in freshwater conditions, and that the structure of the two ‘forms’ is identical.The history of the species has been carried back as far as I have been able to trace it (1836) with the actual specimens, described in the different papers, and the more important of these papers are discussed. It will be seen that the material examined was derived from every country of northern Europe; from Russia, the White Sea, Crimea, and the Baltic, the coasts of Scandinavia, Germany, including the Hamburg water-supply, Denmark, the Netherlands, Great Britain and Ireland, and France as far up the Loire as Nantes.Detailed descriptions and figures of both forms of G. zaddachi are given; and finally, a comparison is made between the species most commonly confused with it, the Arctic species G. wilkitzkii being included because of a suggestion recently made that it might be, not a distinct species, but merely the Arctic form of zaddachi.