Gammarus zaddachi Sexton, 1912

Vader, Wim & Tandberg, Anne Helene Solberg, 2019, Gammarid amphipods (Crustacea) in Norway, with a key to the species, Fauna norvegica 39, pp. 12-25 : 19

6. Gammarus zaddachi Sexton, 1912 (s. Spooner, 1947)

Synonyms: Gammarus zaddachi zaddachi auct.; G. setosus balticus Dementieva, 1931; G. sarsi Reid, 1939 ; G. ochlos Reid , 1945; Lagunogammarus zaddachi auct.

Descriptions and illustrations: Sexton 1942, p. 593, pl. 1, figs 1-7, pl. 2, figs 10-14 (as G. zaddachi , freshwater form); Segerstråle 1947, p. 231, figs 3h-j, 5; Spooner 1947, p. 20, figs

4A-B, 5A-C; Kinne 1954, p. 417, figs 1- 4pp; Dennert et al. 1969, p. 23; Lincoln 1979, pp 239, 243, 249, figs 110a, 111a-b, 114.

Ecology and habitat: Gammarus zaddachi is a brackish water amphipod, living subtidally or in the lower intertidal. It is quite common in the lower intertidal in the inner fjords (where G. duebenii occupies the upper intertidal), but on the outer coast it is generally confined to river mouths (Vader 1977a-b). Also there it lives mainly in the lower intertidal or shallow subtidal, while G. duebenii occupies the higher intertidal. Compared to areas further south (den Hartog 1964, Spooner 1947) G. zaddachi in Norway seems to occupy somewhat less saline waters. Migratory movements, quite conspicuous in French estuaries ( Dennert et al. 1969, Stock 1966, Girisch et al. 1974), have not yet been studied in Norway.

Distribution in Norway: Gammarus zaddachi occurs all along the Norwegian coast, in the right biotopes (Brattegard 1966, Dennert 1973, Vader 1977a-b). On the open coast it is restricted to the outlet of minor streamlets, where it may penetrate quite far inland ( Vader 1977b). In the inner parts of the large fjords, often meso- or even oligohaline, G. zaddachi becomes the dominant amphipod in the lower intertidal, often together with G. oceanicus ( Brattegard 1966, Vader 1977a). The species is absent from Svalbard.

A very aberrant biotope was discovered by the Økland family ( Økland et al. 2011): a population of G. zaddachi lives at 150 m depth in the freshwater lake Eikeren in inland southern Norway.