02. Great crested newt Triturus cristatus, smooth newt Lissotriton vulgaris, and other amphibians in an acidified area of southern Norway surveyed using eDNA and other methods

Abstract - Acid rain for many decades has led to severe acidification of waters in southern Norway. Acidic water can be fatal to gill-breathing vertebrates (i.e. fish and larval amphibians). Great crested newt Triturus cristatus (GCN) - seems to be less tolerant of acidic water than other Norwegian amphibians. Not until 2015 was GCN recorded in Agder, the southernmost county in Norway, when the larvae of this species were found in two ponds. The aim of our investigation, in late spring and summer 2021, was to find out whether GCN was still present in these two ponds and ten others in the same area, which are surrounded by peat bogs and forest. Since this is a marginal and acidic area with probably low numbers of individuals and low detectability, we used three survey methods in combination (funnel traps, nets, and eDNA) and also measured water conductivity and pH. At the same time, the occurrence of other amphibians in the area were investigated; the smooth newt Lissotriton vulgaris, the common toad Bufo bufo, the common frog Rana temporaria and the moor frog Rana arvalis. Using traps and nets, GCN was found in four ponds but in only two of these ponds by eDNA. However, GCN eDNA was detected in three other ponds, showing that a combination of methods gave the most complete result. eDNA of the common toad and the common frog were detected in (almost) all samples but there were few records from traps or nets. Smooth newts were detected in almost all ponds by traps, nets and eDNA, while none of the methods detected the moor frog. Especially when a species is rare at a location, eDNA analysis may be the most efficient method of detection. However, only trapping and netting can give information about breeding. Water pH in late spring and early summer varied from 4.7 to 5.6 (median pH 5.1), which makes this area marginal for amphibian reproduction.