The freshwater shrimp Gammarus lacustris (Malacostraca, Amphipoda) in lakes on the Hardangervidda mountain plateau, southern Norway: distribution and environmental requirements

Abstract

The distribution of the amphipod Gammarus lacustris on the Hardangervidda mountain plateau was mapped by screening published data from 245 lakes in 11 and 16 catchments in western and central/eastern areas, respectively. These data are primarily based on stomach analyses of brown trout Salmo trutta. In central/eastern areas, G. lacustris was recorded in 79% of all the lakes examined, while there are only two former records (4%) in the western area. The distribution pattern of G. lacustris on Hardangervidda appears to be related to environmental conditions. The apparent absence of G. lacustris in the western area may be explained by a combined effect of cold water due to higher deposits of snow and water with low ionic strength as a consequence of its bedrock of Precambrian gneisses and granites with little or no moraine cover. However, lakes in central/eastern areas sustain G. lacustris in spite of dilute water, as G. lacustris has been recorded in 89 lakes of which 28% had calcium concentration <1.0 mg L-1, eight of them with pH <6.0. The lower lethal threshold for calcium concentration seems to be ~0.5 mg L-1. Gammarus lacustris was found in lakes at altitudes of 832 to 1396 m a.s.l. Furthermore, their occurrence increased significantly with lake size, being 69% in lakes <1.0 km2 and 97% in larger lakes. The number of refugia with better water quality is likely to increase with lake size. Gammarus lacustris is highly searched for as prey by all size groups of brown trout (15-45 cm). Access to proximity refugia that reduce predation pressure from fish may also increase with lake size. Climate changes are now in progress in this mountain area, and detailed mapping of G. lacustris is important in order to trace future range changes.

The viability of the crustacean Eurycercus lamellatus (Branchiopoda, Cladocera) in a high mountain area in southern Norway

“…This may be reinforced in high altitude lakes with even lower temperatures as documented in western areas. Thus, this small crustacean seems to be more viable in harsh conditions compared to L. arcticus and G. lacustris earlier reported from the same area (Qvenild & Hesthagen 2019;Qvenild et al 2020 Appendix 2. The catch of brown trout and the crustacean species Eurycercus lamellatus, Gammarus lacustris and Lepidurus arcticus in the 100 fishing events in the five study lakes (cf.…”

“…To elucidate the ability of E. lamellatus to withstand high predation pressure from brown trout, we analysed their diet from five lakes at the central part of the plateau throughout the growing season for 15 years (see . In one of these lakes, been shown for L. arcticus (Qvenild & Hesthagen 2019) and G. lacustris (Qvenild et al 2020).…”

Introduced European minnow Phoxinus phoxinus in alpine lakes may increase total mercury concentration in brown trout Salmo trutta

“…Introduced freshwater fish and invertebrate species may restructure food webs and cause major ecological changes, often at the expense of local species (Langeland 1981;Lasenby et al 1986;Miller 1989;Spencer et al 1991;Kolar & Logde 2002;Baxter et al 2004). The crustaceans Gammarus lacustris G. O. Sars, 1863 and Lepidurus arcticus (Pallas, 1793) are among the most important food items for brown trout in lakes on Hardangervidda (L' Abée-Lund & Saegrov 1991;Borgstrøm 2016;Qvenild et al 2020), as well as in other mountain areas in southern Norway (Aass 1969;Lien 1978). European minnow feed on the same prey species (Borgstrøm et al 1985;Museth et al 2010), also indicated by the δ 15 N of the analysed European minnow from lake Skaupssjøen being nearly in the same range as found for brown trout in the analysed allopatric populations.…”