The invasive South American land planarian Obama nungara has spread rapidly throughout Europe through horticultural trade, raising concerns regarding its impacts on soil biodiversity and ecosystem functioning. Despite its expanding distribution, knowledge of the species’ habitat preferences remains limited. We experimentally investigated soil preference in O. nungara using laboratory habitat-choice trials with four commercially available potting soils. Individuals were allowed to move freely between substrates, and their substrate use was recorded. The O. nungara individuals did not select soil type randomly. Most individuals selected the rhododendron soil characterized by low pH, followed by the rose and perennial soil. Planting soil, both with and without extra added lime, was selected less than would be expected by a random choice. These findings suggest that O. nungara prefers acidic substrates, which may facilitate establishment in horticultural environments associated with acidophilic plants and low-pH growing media.
In the context of global amphibian declines, there is need to map local amphibian populations to establish baseline knowledge of potential future species losses. Even in well-studied lakes and ponds within popular recreational areas near urban centres, information on amphibian occurrence can be limited. In this study, the local distributions of Lissotriton vulgaris, Rana temporaria and Bufo bufo were assessed using eDNA analysis in two city forest areas of Kristiansand, Southern Norway. In the forest Baneheia, all three species were detected, although R. temporaria was present in only half of the lakes. In the forest Jegersberg, L. vulgaris was detected in nearly all lakes while B. bufo only in fewer than half, and R. temporaria was not detected. Our results support the public observations system Artsobservasjoner.no that R. temporaria is uncommon in the coastal area of Kristiansand. Comparison of active netting with eDNA analysis indicated that eDNA is a more reliable method for detecting amphibians. Interestingly, larvae of L. vulgaris were observed in one of the lakes in Baneheia inhabited by Salmo trutta, in a shallow bay with dense aquatic vegetation, demonstrating that newts can successfully reproduce alongside trout under certain conditions.
We assessed the translocation of freshwater fish in Norway during the period 2013-2021. These introductions include both regionally alien species and non-native species, excluding the pink salmon Oncorhynchus gorbuscha. A network of 12 agencies, organizations and persons was established to obtain information and report on new introductions. Totally, 287 incidents were reported, mainly from lakes. Altogether, this included 21 translocated species, comprising 12 regionally alien species and nine non-native species. The most frequently translocated among the regionally alien species was pike Esox lucius (36 incidents), Eurasian minnow Phoxinus phoxinus (35), rudd Scardinius eryhrophthalmus (31) and roach Rutilus rutilus (14). Non-native species mainly involved carp Cyprinus carpio (38), tench Tinca tinca (28), brook trout Salvelinus fontinalis (20), pumpkinseed Lepomis gibbosus (15) and goldfish Carassius auratus (10). The highest number of introductions were reported from counties in southern and middle parts of Norway. At least 146 incidents, or about 50% of the introductions, have led to the establishment of viable populations. The primary vectors leading to these introductions were intentional release to establish populations for angling (≈ 60%). The species most often introduced for this purpose was pike, tench, brook trout, lake trout Salvelinus namaycush, rainbow trout Oncorhynchus mykiss and carp. Roach and perch Perca fluviatilis may be stocked as forage fish for pike, but probably also other species. Further, introduction of baitfish such as Eurasian minnow and rudd accounted for about 20% of all cases. The extensive unplanned movement of species may disrupt local biodiversity.
Long term monitoring data from pristine or relatively unimpacted watersheds represent a valuable ecological baseline in the 21st century. Here, we present a 25-year time series of brown trout (Salmo trutta) and Alpine bullhead (Cottus poecilopus) densities in the boreal-subalpine Atna River in Norway (62 °N) and investigate their relationships with discharge and water temperatures. There was an overall negative trend in densities of Alpine bullhead (3 out of 4 sites), a declining trend in densities of age 0 brown trout (2 of 4 sites), and an inconclusive trend for older brown trout (1 of 4 sites). There were substantial fluctuations in densities for both species, and the majority of the variance originated from year-to-year variation. For older brown trout, approximately 33 % of the variance could be attributed to site-level factors, i.e. systematic differences in densities between sites. Concurrently, there were changes in some of the discharge and temperature-related metrics. The lowest flow of the year became gradually higher throughout the period whereas mean discharge in spring decreased. The best supported models showed a negative relationship between fish densities and mean annual discharge (Alpine bullhead and older brown trout) and a negative relationship between density and minimum annual discharge for age-0 brown trout. The models explained only modest amounts of overall variance in the dataset (range 0 to 12 %), but did document a potentially limiting effect on fish densities on an annual basis. We discuss the likely mechanisms by which discharge and water temperature can influence the abundance of brown trout and Alpine bullhead in river systems, and highlight the value of long-term monitoring as a baseline when investigating broad-scale shifts in abundance.
Globalization has intensified the spread of invasive species through human-mediated transport, particularly via horticultural trade through soil contamination of potted plants. The South American land planarian Obama nungara has become a widespread invasive soil-dwelling predator in Europe, preying mainly on earthworms and potentially disrupting soil processes. It reproduces rapidly and has likely relatively broad habitat requirements. In Sweden, the Environmental Protection Agency (EPA) recommends heat treatment as a preventive measure against this species. This study tested the hypothesis that a 15 minutes 40 °C water bath, as recommended by the Swedish EPA, is lethal to O. nungara egg capsules. Thirteen egg capsules were collected from six adult individuals. Every second capsule was subjected to heat treatment, while the remaining served as controls. None of the six heat-treated capsules hatched, whereas five of the seven untreated egg capsules hatched, each producing between five and seven hatchlings after approximately 24 days. These results demonstrate that the recommended heated water bath is effective not only against adults but also against O. nungara egg capsules. In addition, the study provides basic ecological information regarding the species’ reproductive biology. Given the species’ invasive potential and its capacity to spread via potted plants, these findings support the implementation of thermal quarantine treatments in nurseries and plant trade to prevent establishment and spread of this invasive flatworm in northern Europe.
