Upper thermal threshold of Lepidurus arcticus (Branchiopoda, Notostraca) in lakes on the southern outreach of its distribution range

The Arctic tadpole shrimp Lepidurus arcticus has a circumpolar distribution and the Scandes (Fennoscandian Mountains) marks its southernmost limit in Europe. Within this area, 391 natural and 88 regulated lakes with L. arcticus have been identified, of which 87% are above the treeline. The lakes hosting L. arcticus decrease in altitude from south to north, which results from its temperature preferences. The majority of the locations are at a lower lake air temperature than 11°C which is equivalent to a water temperature near 14°C. This is assumed to be near the upper thermal threshold for L. arcticus. In lakes that exceed this average summer water temperature (1 July – 15 September), sustainable populations seem to be rare. In warmer lakes, life cycle mismatches are assumed to explain the absence of L. arcticus, most likely by affecting the embryo and juvenile stages. The distribution appears to be dichotomous, with one large northern area north of 65°N and one separated southern “island”. Only two locations of L. arcticus are known for the area between latitudes 62.88 and 64.39°N. In this part of the Scandes, the lakes are likely too warm to host L. arcticus as most of them are situated below 700 m a.s.l. This may also be the case in the northernmost region, north of 70°N, where only 11 populations are recorded. Most of the lakes in this area typically occurs below 400 m a.s.l. L. arcticus populations are sensitive to fish predation, and dense fish populations may be another stressor limiting its distribution. In contrast to water bodies in the High Arctic where L. arcticus only exists in shallow, fishless ponds, in the Scandes they co-exist with fish in 97% of the findings. Global warming has already modified the environment of the Scandes, and populations of L. arcticus are at threat in many of the small and shallow water bodies at low altitudes.

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

In Norway, the cyprinid European minnow Phoxinus phoxinus has been spread far outside its previous natural distribution area, with lots of establishments in mountain lakes where brown trout Salmo trutta originally was the only fish species. We have analysed δ15N and total mercury (THg) concentration in brown trout from eight lakes, situated between 1031 and 1244 m a.s.l. on the Hardangervidda mountain plateau, southern Norway. One of the lakes is inhabited by brown trout and European minnow, while in the other seven lakes, brown trout is the only fish species. δ15N of brown trout were significantly higher in the population with co-existing European minnow, indicating a higher trophic position of brown trout in this population than in the allopatric populations, probably caused by piscivory, as indicated by frequent occurrence of European minnow in brown trout diet. The mercury concentrations in brown trout from this lake had values up to around 0.4 mg THg per kg wet weight. The concentrations were significantly higher than in the lakes without European minnow, and together with the δ15N values, indicating that translocation and establishment of European minnow may increase the trophic position of brown trout in previously allopatric populations, and thereby also increase the mercury level.

Alien amphipods (Arthopoda; Crustacea) in the Tista Estuary, Halden, southeastern Norway

Two new amphipods for Norway Melita nitida and Corophium multisetosum (Crustacea; Amphipoda) were registered in brackish waters in the Tista Estuary in Halden, southeastern Norway. Both species were found in the samples from Tista’s outlet into the Idde Fjord, C. multisetosum in the beach zone and M. nitida at about 4 m depth. Melita nitida is a North American species first found in Europe in the Netherlands in 1998, and since then dispersed into the Baltic Sea via the Kiel Canal and now also found several places on the German Baltic Sea coast and in the Black Sea. Corophium multisetosum was collected even before the 1920s in Western Europe, and is considered native for Europe, whereas its relationship to North America is more ambiguous. From the British Isles and the Netherlands, it seems to have spread to Germany, Poland, Denmark and Sweden, and at present Norway. Until now the two species were found in small numbers at the Norwegian sites and their influence on the total benthic community is probably negligible in this initial phase. The Tista Estuary in Halden apparently appears to be a hotspot for alien brackish water species in Norway. Generally estuaries, with their combination of brackish water jointly with their unsaturated ecological niches and intensive international ship traffic, seem to possess the highest potential infection rate for aquatic systems with alien acrozoobenthic species.

Bombus (Megabombus) consobrinus Dahlbom, 1832 in the European North of Russia: its distribution and foraging preference

The focus of this study is to summarize the data on the distribution and foraging preference of Bombus (Megabombus) consobrinus Dahlbom, 1832 in the European North of Russia. The range of B. consobrinus in this region mostly repeats the disjunctions of the range of Aconitum septentrionale that is also known in Scandinavia. In other regions of Northern Eurasia, the close relationship of B. consobrinus with Aconitum is not obvious. This bumblebee species may be regarded as oligolectic in Northern Europe and the European North of Russia. We assume the presence of a coadaptive relationship of this bumblebee species with A. septentrionale in this region that presumably have been caused by the complex history of B. consobrinus in the European North.

Distribution and genetic diversity of two earthworms, Helodrilus oculatus and Satchellius mammalis (Clitellata: Lumbricidae) in Scandinavia

We report on the Scandinavian distribution of two earthworm species, Helodrilus oculatus and Satchellius mammalis. Both appear relatively new to the Scandinavian Peninsula, as they were not included in the monographic revisions of the earthworm fauna of Sweden and Norway in the mid-1900s. We provide recent records of both species from Norway and Sweden, H. oculatus also from Denmark, and haplotype networks of four markers (COI, 16S, H3, and ITS2) are used to visualise the genetic diversity within each species. There is moderate genetic variation in COI for both taxa, and for H. oculatus, there is a West-East division between the specimens from Norway, Gothenburg (western Sweden) and Bavaria (Germany), and the ones from eastern Sweden and the Bornholm island (easternmost Denmark). This could potentially be explained by different origin and colonisation routes. In the other markers the variation is limited, and in the nuclear genes no pattern to support this split is seen. We also analyse the phylogenetic positions of H. oculatus and S. mammalis in the family Lumbricidae by combining our data (including also some12S, 18S and 28S sequences) with a published dataset. We conclude that neither Helodrilus nor Satchellius are monophyletic. Helodrilus oculatus (type species of Helodrilus), however, forms a clade with some of its current congeners.

The helminth fauna of brown trout (Salmo trutta) from a sub-alpine lake revisited after 40 years with introduced European minnow (Phoxinus phoxinus)

The helminth fauna of brown trout (Salmo trutta) in the Norwegian subalpine lake, Øvre Heimdalsvatn was studied by examination of gills, eyes, body cavity, kidney, stomach, pyloric region and intestine in a total of 112 brown trout randomly sampled in June, July, and September 2011. Ten helminth species, Discocotyle sagittata, Phyllodistomum umblae, Crepidostomum farionis, C. metoecus, Diplostomum sp., Proteocephalus sp., Cyathocephalus truncatus, Dibothriocephalus ditremus, D. dendriticus, and Capillaria sp. were identified. These data were compared to data from the period 1969 to 1972, just after the first record of the European minnow (Phoxinus phoxinus) in 1969. All ten helminth species, except D. dendriticus, were also present in 1969–72. However, a few major changes in infection intensities have occurred. The cestode D. ditremus and the trematode Diplostomum sp., both with piscivorous birds as final hosts, had markedly higher relative densities (abundance) in brown trout in 2011 compared to 1969–72, while the two Crepidostomum species showed a substantial decline in relative densities. We suggest that these changes may be indirectly related to the establishment and subsequent population increase of European minnow in the lake. The abundance of minnows may have increased the food basis for the piscivorous birds, primarily mergansers and the black-throated diver that now regularly forage in the lake. In addition, there have been changes in the littoral invertebrate community, including species serving as intermediate hosts of some of the brown trout parasites.

Walleye pollock Gadus chalcogrammus Pallas, 1814 found north of Spitsbergen indicates a Pacific-Atlantic connection in the species

A small (36.5 cm) female walleye pollock Gadus chalcogrammus Pallas, 1814 was caught north of Spitsbergen in2011. The specimen had a high number of pyloric caeca (n=109), indicating a Pacific origin. The record is the firstevidence of a possible input to the small Atlantic population of walleye pollock from the large populations on thePacific side.

The invasive amphipod Gammarus tigrinus Sexton, 1939 conquering the north of Europe using a new pathway: the first recordings from Norway

The invasive amphipod Gammarus tigrinus has during the last decades spread to large parts of Northern Europe, mainly using pathways eastwards from The British Isles to Continental Europe and further northeast into the Baltic Sea. From the coastline it has to some extent spread further inland, especially in topographically low-relief landscapes with highly polluted rivers. This account reports another geographical direction of dispersal, towards north into Southern Norway. In coastal brackish-water regions G. tigrinus may displace other gammarids. Large parts of Norway consist of high-relief landscapes close to many estuaries, so the further spread into this country is doubtful. However, if the taxon can avoid the initial barriers using vectors and spread into new watercourses above such barriers and thrive in this new ambient water chemistry, it may have large negative influence on the other benthic fauna. But Norwegian lakes and rivers are most probably too electrolyte-poor to support this species. However, in estuaries and other brackish waters along the coast, at least in the southern part of Norway, the species will thrive. Gammarus tigrinus is the only known intermediate host for the native American acanthocephalan parasite Paratenuisentis ambiguus, which has the American eel as its main host. This parasite also infects the European eel, and this poses an additional threat to the already endangered eel in Norwegian rivers where G. tigrinus has been recorded.

Factors determining parasite abundance in European perch, Perca fluviatilis, European whitefish, Coregonus lavaretus, and Arctic charr, Salvelinus alpinus, in an oligotrophic lake, southern Norway

Time and spatial variations in macroparasite status were investigated in European perch, Perca fluviatilis, European whitefish, Coregonus lavaretus, and Arctic charr, Salvelinus alpinus in Lake Norsjø (Southern Norway), based on gillnet fishing in three locations in the spring, summer, and fall 2018. In addition, length, weigth, age, sex, δ13C, and δ15N were determined. Parasite abundance was modelled using negative binomial generalized linear models in relation to fish metrics, season, and sampling location. The most prevalent parasite species were determined by the diet and habitat of the host. European perch was mainly infected by acanthocephalans, European whitefish mainly infected by acanthocephalans and cestodes, and Arctic charr mainly infected by cestodes. The most prevalent parasites in European perch are transmitted by benthic animals. Parasites in European whitefish are transmitted by both benthic animals and copepods, while the most prevalent parasites in Arctic charr are copepod transmitted. This corresponds well with the δ13C signatures in the three species, indicating that European perch primarily fed in the littoral zone (δ13C: -24.9 ± 2.5 ‰), Arctic charr in the pelagic and profundal zone (δ13C: -29.4 ± 1.1 ‰), while European whitefish both fed in the littoral and pelagic zone (δ13C: -28.3 ± 2.3 ‰) of Lake Norsjø. Individual abundances of parasites depended on host age, length, sex, δ15N, and season. Positive correlations between parasite abundance and host age, length, or trophic level measured as δ15N were most common, and occurred in all three host species. Many parasites accumulate with age, and larger hosts provide more diverse habitats for parasites.

Distribution, identification and range expansion of the common Asellidae in Northern Europe, featuring the first record of Proasellus meridianus in the Nordic countries

Two out of the three common Asellidae species in Northern Europe are increasing their ranges, aided by humanactivities. Here we report the discovery of Proasellus coxalis (Dollfuss 1892) in new areas in Norway and thediscovery of Proasellus meridianus (Racovitza 1919) for the first time in the Nordic countries, verified withDNA barcoding. A new, detailed photo-identification guide to Asellus aquaticus Linnaeus 1758, P. coxalis andP. meridianus is presented. In addition to head pattern, attention is drawn to the female pleopods as an easy way to differentiate between the two genera. Then detailed examination of male pleopods 1 and 2 can differentiate between P. coxalis and P. meridianus. The origins, competitive relationships and potential dispersal mechanisms of the two introduced species and the native A. aquaticus are explored. By examining the shipping activity at the small, freshwater port where P. meridianus was found, we highlight the great connectivity between many European brackish and freshwater ports and possible pathways for species transfer. The risk of trans-oceanic freshwater to freshwater (not just brackish and saltwater) species transfer through ballast water needs to be better communicated. Proasellus coxalis may have been introduced to the river system of Lake Stokkalandsvatnet together with fish transported in microaquaria used as live bait for fishing.