Ecology and distribution of the Arctic Tadpole Shrimp Lepidurus arcticus (Branchiopoda, Notostraca) in the Fennoscandian Mountain Range and on the Svalbard Archipelago

9 Fauna norvegica 2025 Vol. 44: 9–27. Review paper Ecology and distribution of the Arctic Tadpole Shrimp Lepidurus arcticus (Branchiopoda, Notostraca) in the Fennoscandian Mountain Range and on the Svalbard Archipelago Tore Qvenild 1 , Arne Fjellheim 2 , Trygve Hesthagen 3 and Hanna-Kaisa Lakka 4 , 5 , 6 Qvenild T, Fjellheim A, Hesthagen T and Lakka H-K. 2025. Ecology and distribution of the Arctic Tadpole Shrimp Lepidurus arcticus (Branchiopoda, Notostraca) in the Fennoscandian Mountain Range and on the Svalbard Arch ipelago . Fauna norvegica 44: 9 – 27. Lepidurus arcticus is frequently found at sea level in the Svalbard archipelago, extending further south from 80°N into the tundra zone and at increasing altitudes in the Fennoscandian Mountain Range (Scandes) down to 59°N, spanning 2300 km. In this region, there are records of Lepidurus arcticus in at least 686 locations. In Svalbard, it is noted in 87 fishless ponds and two rivers with anadromous Arctic charr. In Bear Island, it inhabits 103 fishless ponds, eight lakes, and three rivers containing resident Arctic charr. In the Scandes, it is found in 483 locations, predominantly in deep, large lakes with fish. This demonstrates a greater adaptability to various habitats than other notostracan species. The species’ ability to withstand significant environmental changes since its emergence is attributed to its resilient eggs, which can endure both freezing and desiccation and remain viable for decades. Additionally, its reproductive flexibility, which creates egg banks of overlapping generations, helps buffer the population against environmental variability. While the embryonic phase may persist for decades in the Arctic, both the embryonic and postembryonic phases are typically completed within a year in the Scandes. Lepidurus arcticus can reproduce both sexually and asexually. Asexual reproduction enhances dispersal abilities, as single eggs or individuals can establish new populations. Predicted warming of freshwater habitats may significantly impact Lepidurus arcticus, as water temperature limits its distribution. With rising temperatures, L. arcticus will likely expand its range into the colder territories of Svalbard. In the Scandes, prolonged warmth could restrict its range, yet it may ascend in altitude in southern Scandes. In Svalbard, warmer water and prolonged open water seasons may boost production. This could make the lakes more similar to those in Bear Island, and thus, coexistence with fish could become more common. Therefore, baseline studies are needed for cold-adapted freshwater species such as Lepidurus arcticus. ISSN: 1891-5396 (electronic). doi: https://doi.org/10.5324 /fn.v44i0.5919 . Received: 2024-06-11. Accepted: 2025-06-10. Published online: 2025-06-24. Keywords: Lepidurus arcticus, Bear Island, distribution, Arctic freshwater biodiversity, climate, ecological changes 1. Solhellinga 29 J, NO-2315 Hamar, Norway 2. Sandalsbakken 2, NO-4022 Stavanger, Norway 3. Lundavegen 330, NO-2690 Skjåk, Norway 4. Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland 5. The University Centre in Svalbard, P.O. Box 156, NO-9171 Longyearbyen, Norway 6. Kilpisjärvi Biological Station, University of Helsinki, Käsivarrentie 14622, FI-99490 Kilpisjärvi, Finland Corresponding author: Tore Qvenild E-mai l : [email protected] Qvenild et al .: Lepidurus arcticus in Fennoscandia and the Svalbard Archipelago Fauna norvegica 44: 9–27. 2025 10 (Longhurst 1955). In contrast, L. arcticus is found in the circumArctic regions. Adaptation to warm, arid desert pools, which demand rapid development and reproduction, has prepared this species for another distinct environment where favourable conditions for life emerge seasonally for brief durations. Consequently, the existence in temporary arid desert pools may have equipped this notostracan species to survive in Polar desert pools, where the growth period is similarly abbreviated. Except for L. arcticus, Lepidurus couessi Packard, 1875, the closest relative to L. arcticus (Hessen et al. 2004), held the distinction of being the northernmost species among the other Notostraca in both Canada where it is found north to 50°N (Hann & Loonsberry 1991), compared to 65°N in sub-arctic Europe (Brtek & Thiery 1995). In general, notostracan species are restricted to ephemeral waters without fish (Brendonck et al. 2008; Vanschoenwinkel et al. 2012). Likewise, L. arcticus is restricted to temporal ponds without fish in the High Arctic, but further south, in Arctic and subarctic regions, it is also frequently found in permanent lakes with fish (Sømme 1934; Qvenild et al. 2021). Here, L. arcticus was first documented as fish prey by Huitfeldt-Kaas (1911) under the name Apus glacialis (Braem, 1893), with several synonyms used in early 20th-century literature (Rogers 2001). The species’ ecological sensitivity is pronounced in Arctic and alpine habitats, where baseline studies are crucial for predicting global warming impacts on cold-water-adapted species like L. arcticus. In general, a broader knowledge and attention on large branchiopods are needed (O´Brien & Helm 2025). This paper aims to compile updated knowledge and historical records of L. arcticus across its extensive range, from 80°N in Svalbard to 59°N in the Fennoscandian mountains, highlighting its environmental adaptability and resilience. MATERIAL AND METHODS Definitions In this paper we distinguish between regulated and natural lakes, which are simply lakes without damming. For convenience, we use the term Lepidurus lake to refer to a lake or pond of any size hosting L. arcticus, including regulated lakes. In this paper the summer period is defined as July 1st to September 15th. The Svalbard archipelago consists of Spitsbergen and the islands nearby in the High Arctic (74– 81°N, 10–35°E), hereafter called Svalbard. In addition, the archipelago includes the outlier Bear Island in the Low Arctic. The Fennoscandian mountain range, also known as the Scandes, spans from 59°N to 70°N and 8°E to 11°E, covering roughly 1700 kilometres and featuring a diverse terrain from subarctic to alpine regions. Description of the area Freshwater localities in Svalbard are typically found in coastal, lowland areas below 50 m (Lakka 2013). These locations can be significantly impacted by glacier runoff, which results in high sediment loads, irregular flows, and persistently low water temperatures even during summer months (Svenning 2015). In contrast, most permanent clearwater lakes achieve higher temperatures in summer. Ice break-up generally occurs from July to late August, allowing lakes to remain ice-free for up to three months, although some may remain partially or permanently ice-covered (Svenning 2015; Lakka 2013). The absence of a comprehensive database for lake areas in Svalbard has necessitated the use of polygons from TopoSvalbard - INTRODUCTION The Branchiopoda class, except for the Cladocera, is often referred to as «large branchiopods», although this name lacks a phylogenetic or taxonomic foundation (Brendonck et al. 2008). Within the Branchiopoda, the order Notostraca includes the Triopsidae family, with the two genera Triops Schrank, 1803, and Lepidurus Leach, 1819, as well as extinct members of the stem lineage (Geyer et al. 2024). These crustaceans are notable for their evolutionary stasis, showing little to no morphological changes over extensive geological periods since their initial divergence. The term «living fossil» is often used for such species or genera. Historically, Notostraca fossils from the Lower Triassic Voltzia Sandstone Lagerstätte in northeastern France were linked to Triops cancriformis (Bosc 1801), claiming it as the oldest continuously existing animal species at 240 million years (Geyer et al. 2024). This assertion has been discredited due to the lack of molecular evidence supporting a relatively recent Cenozoic radiation (Vanschoenwinkel et al. 2012). Moreover, a re-evaluation classified these fossils as Apudites antiquus, an extinct stem lineage species (Geyer et al. 2024). Despite this, the concept of a «living fossil» can be defined as a taxon belonging to a group with a long evolutionary history, retaining several primitive characteristics, and having few living relatives (Vanschoenwinkel et al. 2012). By this definition, members of the order Notostraca can generally be considered living fossils. Notostracan species are characterised by hypervariability in numerous morphological characters, despite their long-term stability in gross morphology. The taxonomic distinctions within the crown group remain unresolved. However, the genera Triops and Lepidurus can be differentiated by the presence of the supra-anal plate found in Lepidurus but absent in Triops (Longhurst 1955). Morphological studies of the Arctic tadpole shrimp, Lepidurus arcticus (Pallas, 1793), have uncovered notable variations in the supraanal plate’s size, with Svalbard populations having significantly shorter plates (Lakka 2015). These populations exhibit greater phenotypic plasticity compared to those in Fennoscandia (Lakka 2013, 2015; Järvinen et al. 2014). Genetically, L. arcticus is distinctly different from other Lepidurus species (Hessen et al. 2004; Vanschoenwinkel et al. 2012). Research on 48 populations across a wide geographical range identified two haplogroups (A and B) with five haplotypes (A1-A3, B1-B2) (Hessen et al. 2004). A distinctive pattern is the separation of haplogroups between Bear Island (haplotype B1) and Svalbard (haplotype A1). Haplotype A1 is also found in Norway and Russia, suggesting possible dispersal by migratory birds. This is likely because it has been demonstrated that at least 57 bird species consume large branchiopods (Dolmans et al. 2025). The Notostraca are cosmopolitan crustaceans whose ecology is closely connected with ephemeral waters in warm, arid regions Figure 1. The Arctic tadpole shrimp Lepidurus arcticus is a large (<4 cm) cold-adapted Arctic species living in freshwater lakes and ponds. Photo: Hanna-Kaisa Lakka. Qvenild et al .: Lepidurus arcticus in Fennoscandia and the Svalbard Archipelago Fauna norvegica 44: 9–27. 2025 11 arcticus may appear later and might not be visible until September, if at all. Detecting L. arcticus can be challenging, necessitating repeated investigations. Fish predation greatly diminishes L. arcticus populations, making detection difficult when fish are abundant. Moreover, in Arctic conditions, repeated sampling is essential, as a large portion of the population may be dormant in the egg bank. DISTRIBUTION Lepidurus arcticus has a circumpolar distribution in the northern hemisphere, spanning both North America and Siberia (Rogers 2001; Hessen et al. 2004). The species was first described following a Siberian expedition in 1768, which included Peter Simon Pallas. Lepidurus arcticus is found as far north as 74°N in the eastern Novaya Semlya archipelago (Veckhof 1997) and extends to the Kuril Archipelago (Sayenko & Minakawa 1999). Rasshua Island (47°N) in the middle Kuril Islands is likely the southernmost limit of L. arcticus in Asia. These islands experience frequent summer fog and are snowcovered for much of the year. Lepidurus arcticus is also common in Iceland (Scher et al. 2000; Eiríksson et al. 2021) and Greenland (Sømme 1934; Røen 1962; Jeppesen et al. 2001). Dated sediment remains of L. arcticus show that the species once had a broader range, including Denmark (Økland & Økland 2003), Ireland, Scotland, and the Isle of Man (Mitchell 1957). Distribution in Svalbard The initial record of L. arcticus in the Svalbard archipelago dates back to 1878 in Advent Bay (Richard 1878, cited in Sømme 1934). By the 1930s, it had been documented in at least 16 locations (Sømme 1934). Due to logistical challenges in Svalbard, most records from Spitsbergen come from areas near Longyearbyen and Ny-Ålesund (Figure 2), although some findings are from more remote regions. A few observations are reported from the eastern islands, including a pond in Snaddvika, Murchison Bay on Nordaustlandet (80.0°N, 18.8°E), which might be the northernmost record in Svalbard, albeit lacking an exact date and position (Sømme 1934). There is also an unspecified record from Barentsøya (Richard 1898, cited in Sømme 1934). Bennike & Hedenås (1995) found sediment remains of L. arcticus at four locations in Visdalen on Edgeøya in 1991. Jørgensen & Eie (1993) studied 17 locations on the Mosselhalvøya peninsula in 1977, recording L. arcticus in nine fishless ponds but not in eight lakes hosting Arctic charr (Salvelinus alpinus Linnaeus, 1758). The ponds near Polheim (79.89°N, 16.02°E) are the northernmost properly documented localities for L. arcticus in Spitsbergen, though Sømme (1934) noted a nearby finding in Sorgfjorden (at Treurenberg) at almost the same latitude, which is difficult to pinpoint. In 2010, Lakka (2013) found L. arcticus in one of the four ponds near Polheim. Further northern observations have been made from Reinsdyrflya (79.70°N) (Sømme 1934; Lakka 2013). Recent studies have thoroughly investigated the Lepidurus localities in the vicinity of Ny-Ålesund. In 2010, Lakka (2013) examined nine locations, finding L. arcticus in seven ponds. In 2015, Dimante-Deimantovica et al. (2015) studied eleven locations, with only one record of L. arcticus (information provided by Bjørn Walseng, pers. comm.). Calizza et al. (2022) investigated 18 locations, recording L. arcticus in nine, including three new habitats not previously studied (Dimante-Deimantovica et al. 2015; Lakka 2013). At least four L. arcticus localities (Storvatnet, Solvatnet, Tvillingvatnet, and Trehyrdingene) and two ponds without L. arcticus (Gluudneset and Goose Pond) were studied in all three projects Norsk Polarinstitutt (https://npolar.no), leading to estimates of roughly 300 lakes, with only 82 exceeding 1 km2 in area. In addition, there are numerous small puddles and ponds (≤ 1 ha) that may dry out in the summer and freeze solid during the winter. Bear Island, lacking glaciers, experiences a longer ice-free period, typically starting in late June and lasting between 2.5 and 3.5 months. Of the approximately 740 freshwater localities in Bear Island, most are shallower than five metres, with only ten lakes reaching depths between five and ten metres (Klemetsen et al. 1985). The deepest lake, Lake Ellasjøen, spans 0.72 km2 and reaches a maximum depth of 34 m. The largest lake, Lake Haussvatnet, covers 1.17 km2. The northern plateau of Bear Island is flat, mostly below 50 m, and features numerous small lakes and ponds. The High Arctic climate is characterised by extreme variations in photoperiod, with continuous daylight long before ice break-up and high ultraviolet radiation intensity. Even before the ice begins to melt, photosynthetically active radiation penetrates through the ice, and the extent of this under-ice radiation and UV exposure is regulated by the thickness of the ice and snow cover (Belzile et al. 2021; Brittain et al. 2020). At ice break-up, the sudden improvement in light conditions in the littoral zone can create an ‘illumination shock’ (see Svenning 2015). In Svalbard, the summer air temperature, fairly constant due to oceanic influence, has seen a notable increase of 1.41°C during the period 2000–2020 compared to the 1961–1990 norm (estimated as a mean from the meteorological stations Bear Island, Hornsund, Isfjord radio, Svalbard airport, and Ny-Ålesund) (https://seklima.met.no). Coastal areas exposed to the open ocean experience higher yearly precipitation, ranging from 402 to 529 mm, while Longyearbyen has a mean yearly precipitation of only 204 mm (mean for the period 2017–2020). The Scandes experiences longer ice-free summers lasting from three to five months. Of the 482 recorded Lepidurus lakes in the Scandes, almost 50% are larger than 1 km2, and most are relatively deep and large. Most lakes reach higher surface temperatures in summer, aligning with observed air temperatures (Qvenild et al. 2021). In contrast to the High Arctic, L. arcticus coexists with fish in 97% of these lakes. Mid-summer days are mostly illuminated even at the southernmost localities (up to 18 hours at 59°N). Temperature data from six meteorological stations in the Scandes indicate an increase of 1.26°C above normal in the period 2000–2019 (Qvenild et al. 2021). The range also creates a rain shadow, resulting in higher precipitation on the western side and drier conditions on the eastern side. Annual precipitation varies from over 2800 mm on the western side to less than 400 mm on the eastern fells. The Scandes, mostly situated above the treeline, are influenced by both marine and continental climates. Sampling of Lepidurus arcticus Multiple sampling techniques, such as bottom samplers (Lakka 2020), sieves (Halvorsen 1973), artificial substrates (Fjellheim et al. 2007), benthic littoral kick samples (Fjellheim et al. 2007), traps and density samplers such as ‘peltipelle-sampler’ (Lakka 2013), have been used. Visual observing is also frequently used (Lakka 2020). However, in lakes and ponds with fish, fish stomach analyses proved to be the most effective method, particularly when L. arcticus was present in low numbers or exhibited a patchy distribution (Fjellheim et al. 2007; Qvenild & Hesthagen 2019). The timing of sampling is crucial, as the abundance of L. arcticus varies throughout the season (Qvenild & Hesthagen 2019). Most fish investigations occur from August to October when L. arcticus is more abundant. In cold summers, L. Qvenild et al .: Lepidurus arcticus in Fennoscandia and the Svalbard Archipelago Fauna norvegica 44: 9–27. 2025 12 Figure 2. Lepidurus arcticus has been reported in 81 fishless puddles and ponds in Spitsbergen, in addition to the outlet rivers from Lake Straumsjøen and Lake Linnévatnet, which both host anadromous Arctic charr. In addition, Lepidurus arcticus is found in one locality at Nordaustlandet, one on Barents Island, and four localities with sediment remains on Edge Island. Norwegian Mapping Authority CC BY 4.0. Qvenild et al .: Lepidurus arcticus in Fennoscandia and the Svalbard Archipelago Fauna norvegica 44: 9–27. 2025 13 the north and southern banks (Colesbukta, Grønnfjorden, and Kapp Linné). No lakes with Arctic charr have yielded positive findings despite extensive stomach analyses, except for anadromous Arctic charr caught in the outlet rivers of Straumsjøen (Aas 2007; Borgstrøm et al. 2018) and Lake Linné (Ebne 2009). Large, shallow lakes of Flydammane on Erdmans Tundra in Ymerbukta all hosted L. arcticus (Olofsson 1918; Dimante-Deimantovica et al. 2015), as did most ponds in Randvika (Dimante-Deimantovica et al. 2015), Aldegondabreen (Dimante-Deimantovica et al. 2015), Coles Bay (Olofsson 1918), and all at Kapp Linné (Lakka 2013). Thus, L. arcticus seems prevalent in small, fishless water bodies in the Isfjorden area, though year-to-year variation is significant. Further south, only three areas have been investigated. In Sveagruva, van Miejenfjorden, Olofsson (1918) found no records of L. arcticus in five freshwater locations. On the western coast, at Kapp Bruunodden, an old record exists (Sømme 1934). Some activity has occurred at the Polish station in Hornsund, with Janiec (1996) noting L. arcticus in three nearshore ponds in 1989. Genetic studies were conducted in two lakes at Fuglebergsletta by Wojtasik & BrylkaWolk (2010), with a replicate in Fugledammen by Luoto et al. (2016). Wojtasik & Brylka-Wolk (2010) reported L. arcticus in 13 of 50 water bodies examined in Hornsund, though no further site details are provided. Thus, L. arcticus populations do exist in this area. Lepidurus arcticus is commonly recorded in numerous fishless water bodies in Spitsbergen, ranging from a 6 m2 pond in Nybyen (Lakka 2013) to the 15 ha Flydammane on Erdmans Tundra (DimanteDeimantovica et al. 2015). In total, L. arcticus has been documented in at least 81 fishless puddles and ponds in Spitsbergen, plus one locality on Nordaustlandet, one on Barents Island, and four sediment remains sites on Edge Island. Lepidurus arcticus is also noted in two outlet rivers that host anadromous Arctic charr, totalling at least 89 documented localities in Svalbard. Distribution in Bear Island Lepidurus arcticus is frequently found in Bear Island (Klemetsen et al. 1985). In a survey conducted in 1998/1999, Hessen et al. (2004) Figure 3. In Svalbard, a typical habitat for Lepidurus arcticus is a shallow pond. An example is this artificial pond situated near the old coal mines in Longyearbyen. The pond is dammed and gets its water from a glacier river. Photo: Hanna-Kaisa Lakka. (Calizza et al. 2022; Dimante-Deimantovica et al. 2015; Lakka 2013). Lepidurus arcticus was also detected in Lake Storvatnet in 1980 (Økland & Økland 2003). Lake Solvatnet has been studied on multiple occasions, with Lepidurus eggs collected for laboratory experiments in 2014 and 2015 (Mancinelli & Pasquali 2016; Pasquali et al. 2019). Despite the lack of findings in many locations, L. arcticus appears to be very common in the area, with an early observation near the Conway glacier on Kongsfjorden’s eastern shore (Sømme 1934). Lepidurus arcticus has long been known from the Isfjorden area, with thorough studies by various authors. In Adventdalen, both Sars (1885–91) and Richard (1898) (cited in Sømme 1934) reported L. arcticus from small ponds sampled in 1878 and 1897, respectively. In 1910, Olofsson (1918) found it in a lake (Teich XXI), likely the same location investigated in 1928 by Thor (1930), which he referred to as Isdammane. Lakes and ponds in this area served as drinking water and ice supplies for Longyearbyen, later dammed into the present Isdammen in 1960. In recent years, L. arcticus has been sampled in many localities nearby Isdammen (Lakka 2013; DimanteDeimantovica et al. 2015). A find was noted six kilometres further into the valley at ‘Engelskhytta’ (Thor 1930). Ponds in Longyeardalen also host L. arcticus (Lakka 2013), though it has not been observed annually in all city ponds since 2010 (Coulson, pers. comm.). On Diabasodden, northeast of Longyearbyen, a pond was positively investigated by both Olofsson (1918) and Dimante-Deimantovica et al. (2015). Expeditions have visited both sides of the Billefjorden area. On Kapp Napier, Olofsson (1918) failed to find the species in six ponds in 1910, but positive findings were made in 1970 and 2014 (Artsdatabanken; Dimante-Deimantovica et al. 2015). In Mimerdalen, three well-defined lakes repeatedly examined as water supplies for Pyramiden’s early settlement also yielded positive findings (Lakka 2013; Dimante-Deimantovica et al. 2015). In Lake Goluboye, two kilometres further into the valley, L. arcticus was found (DimanteDeimantovica et al. 2015). Two ponds in this area also hosted L. arcticus. Surveys in the outer Isfjorden area include both Ymerbukta in Qvenild et al .: Lepidurus arcticus in Fennoscandia and the Svalbard Archipelago Fauna norvegica 44: 9–27. 2025 14 Figure 4. In Bear Island, Lepidurus arcticus is found in 114 localities, of which 103 are fishless ponds. At least eight of the 12 lakes that contain resident Arctic charr host Lepidurus arcticus. In addition, Lepidurus arcticus is recorded in three rivers, all with resident Arctic charr populations. Norwegian Mapping Authority, CC BY 4.0. Qvenild et al .: Lepidurus arcticus in Fennoscandia and the Svalbard Archipelago Fauna norvegica 44: 9–27. 2025 15 collected samples of L. arcticus from 29 ponds scattered across the island. Subsequently, in a more extensive survey of 109 ponds on the northeastern plateau, L. arcticus was detected in 71 (65%) of them (Klausen 2012) (coordinates provided by Sigurd Einum, pers. comm.). Lepidurus arcticus is abundant in three rivers – Engelskelva, Jordbruelva, and Lakselva – all of which support populations of resident Arctic charr (Klemetsen et al. 1985). In Bear Island, L. arcticus is also present in lakes where it coexists with Arctic charr. Of the twelve lakes studied, all hosting Arctic charr, L. arcticus was found in eight (Klemetsen et al. 1985; Berg et al. 2010; Evenseth et al. 2005). Overall, L. arcticus is present in 114 locations: 103 fishless ponds, eight lakes, and three rivers with resident Arctic charr populations (Figure 4). Distribution in the Scandes The Scandes represent the southernmost limit of L. arcticus occurrences in Europe (Økland & Økland 2003; Qvenild et al. 2021). The species was first recorded in Norway by G.O. Sars during his mountain trip to Filefjell in 1863 (Sars 1864). In Sweden, an early record exists from the Sulitjelma area (Lilljeborg 1877, cited in Sømme 1934). By the early 20th century, L. arcticus had been reported from at least 37 localities: 29 in Norway and 8 in Sweden (Sømme 1934). The first Finnish observation was from a pond near the Halti fells in 1955 (Koli 1957). A summary of records for the Norwegian mainland was provided by Økland & Økland (2003). A recent study from the Scandes reported L. arcticus in 391 natural and 88 regulated lakes, spanning latitudes from 59 to 71°N and elevations from 74 to 1524 m a.s.l (Qvenild et al. 2021). Norwegian localities extend further south and north than those in Sweden and Finland. On the Norwegian mainland, 315 natural lakes and 79 regulated lakes were recorded. Most Swedish records of L. arcticus were found in northern river systems, with 78 locations documented, including eight regulated lakes. In 2023, an additional record was made in a small pond (68.7024°N, 20.8518°E) with Arctic charr in Northern Sweden (Lakka, unpubl.). Finnish Lepidurus lakes in the Scandes are situated in the northwestern part of Finnish Lapland above 666 m a.s.l (Lakka 2020). Here, L. arcticus was found in seven localities, one of which is a regulated lake outside the Scandes (Lake Inarijärvi). Recently three more observations of L. arcticus are made: Lake Pitsusjärvi (69.2292°N, 21.2767°E), Lake Jápmajávri (69.1186°N, 21.4725°E), and Pond ‘Luonnontutkija’ (69.1598°N, 21.1606°E) (Lakka, unpubl.). In total, 686 localities hosting L. arcticus are known in the Scandes. The distribution in the Scandes appears to be dichotomous, with a large northern area north of 64°N and a smaller southern ‘island’ south of 63°N. Southernmost records are at altitudes ranging from 489 to 1524 m a.s.l, while north of 70°N, only 11 natural lakes are located below 327 m a.s.l. In this region, mountains are low, with few reaching more than 400 m a.s.l. The altitudes of natural lakes with L. arcticus decline towards the north, and regulated lakes are often at lower altitudes than natural ones. Of natural Lepidurus lakes, 87% are situated above the treeline (Qvenild et al. 2021). In contrast to Svalbard, L. arcticus normally coexists with fish in the Scandes. Fish status was obtained in 379 of 391 Lepidurus lakes (Qvenild et al. 2021), documenting ten fish species. Most lakes host brown trout (89%) and Arctic charr (>23%), particularly in the northern part. The invasive Eurasian minnow Phoxinus phoxinus (L., 1758) is now established in at least 9% of Lepidurus lakes. Other species include grayling Thymallus thymallus (L., 1758), burbot Lota lota (L., 1758), perch Perca fluviatilis L., 1758, whitefish Coregonus lavaretus (L., 1758), ninespine stickleback Pungitius pungitius (L., 1758), northern pike Esox lucius L., 1758, and non-native American brook trout Salvelinus fontinalis (Mitchill, 1814). In lake Inarijärvi, outside the Scandes, three more species are documented: salmon Salmo salar L., 1758, three-spine stickleback Gasterosteus aculeatus L., 1758, and non-native lake trout Salvelinus namaycush (Walbaum, 1792). In a study of 124 natural lakes on Hardangervidda in southern Norway, L. arcticus was most frequently found at altitudes of 1100– 1199 m a.s.l, with an occurrence rate of 80% (Qvenild & Hesthagen 2019). A thermal deficit may limit the species at high latitudes and altitudes. On Hardangervidda, the highest lake hosting L. arcticus is Lake Kolsnutgryslane at 1386 m a.s.l. They may exist at higher altitudes, as recorded in Lake Rygghøtjønne at 1524 m a.s.l further north (Økland & Økland 2003). Cold water also limits reproduction in Svalbard populations (Olofsson 2018; Lakka 2015). LIFE HISTORY TRAITS Reproduction and recruitment For many species, there is a shift from facultative parthenogenesis in temperate regions to obligate parthenogenesis in the Arctic (Hessen et al. 2004). Asexuality enhances dispersal capabilities, as single eggs or individuals can establish new populations. Lepidurus arcticus exhibits both parthenogenesis and sexual reproduction (Wojtasik & BrylkaWolk 2010; Lakka 2015). Males are rarely found in studied populations. In Spitsbergen, males made up only 2.6% of the total sample (N = 789) from 19 ponds (Lakka 2015). In the six ponds where males were present, the male-to-female ratio averaged 1:16. Thus, sexual reproduction in L. arcticus may be more common than previously thought. Lakka (2015) documented males as far north as Reinsdyrflya (Kilneset at 79.70°N). Selective pressures affect the sexes differently. Male fitness improves through successful mate searching, while female reproductive potential increases with larger body sizes (Lakka 2015). Smaller males searching for females face greater risks due to the increased chance of encounters with cannibalistic females. Cannibalism, a form of extreme sexual conflict, may explain the low number of males in populations. Injuries caused by birds and conspecifics, including cracks and holes in carapaces and broken cercopods, were observed in L. arcticus populations in Svalbard (Lakka 2013). Maturity is determined by the carapace length when foot capsules (ovisacs) appear on the 11th pair of legs (Miller 1980). In Spitsbergen, L. arcticus reached maturity at 4.0 mm (range 4.0–9.1 mm) in carapace length (Lakka 2013). Temperature, growing season length, and salinity influence the size of maturing females. In other studies, females reached sexual maturity at 5.0 to 8.9 mm in carapace length (Sømme 1934; Arnold 1966; Borgstrøm 1970). In Spitsbergen, egg size was studied in 14 populations (Lakka 2013). Sizes ranged from 0.2 to 1.1 mm, with the most common sizes being between 0.6 mm and 0.8 mm. Early in the season, small L. arcticus produced small to medium-sized eggs. When carapace length reached approximately 8 mm, they began producing eggs larger than 0.8 mm. Eggs sampled in some small ponds at Barrow in Alaska had a size of 0.71 mm (weight 33±0.5 µg C) (Miller 1980). The number of developing eggs carried internally is linearly related to female length, with full-grown females (total length 25–30 mm) carrying up to 60–70 eggs in their lifetime (Miller 1980). Egg shape can be irregular before rounding inside the egg capsules (Lakka 2013). Externally, one to three eggs are carried at a time (Miller 1980), but in Svalbard, Lakka (2013) found females carrying up to Qvenild et al .: Lepidurus arcticus in Fennoscandia and the Svalbard Archipelago Fauna norvegica 44: 9–27. 2025 16 Figure 5. Distribution of 479 lakes hosting Lepidurus arcticus in the Scandes (Qvenild et al. 2021). Natural lakes (N = 391) are indicated by blue dots and regulated lakes (N = 88) with red dots. In addition, four new localities were recently mapped (not in the map). Norwegian Mapping Authority, CC BY 4.0. Qvenild et al .: Lepidurus arcticus in Fennoscandia and the Svalbard Archipelago Fauna norvegica 44: 9–27. 2025 17 twelve eggs. These eggs harden over a few days before release. In Spitsbergen, females mainly produced one egg when smaller than 8 mm in carapace length. On average, a single female produced 2.6 eggs (range 0–12 eggs), more than previously observed (Sømme 1934; Arnold 1966; Miller 1980; Vekhoff 1997). Embryonic development: egg laying to hatch Branchiopods have evolved various adaptations to endure the harsh and unpredictable conditions of both Arctic and arid temporary water bodies, which may freeze or dry out unexpectedly (Longhurst 1955). Their encysted embryos enable their progeny to survive periods of desiccation and freezing. These resting eggs, known for their remarkable longevity during dormancy, can withstand multiyear droughts, freezing temperatures, mechanical damage, oxygen deprivation, ultraviolet radiation, and digestion by predators (Rogacki & Brysiewicz 2021). When in a dry or frozen state, these eggs can remain viable for decades or even centuries without the need for rehydration (Brendonck et al. 2008; Hann & Lonsberry 1991). Embryonic development within an egg capsule is affected by temperature. During this phase, embryos may enter dormancy if the cysts undergo desiccation or freezing. It is essential for any organism to receive a minimum amount of thermal input for embryonic development (Gillooly & Dodson 2000). Only a portion of the eggs hatch upon rehydration (Hann & Lonsberry 1991; Fryer 1996; Rogers 2014; Pasquali et al. 2019). This may be explained with egg banks containing eggs of varying ages, with embryos being at different developmental stages. Furthermore, the incomplete hatching of egg batches, even from individual females, might be an adaptation to the highly variable environments found in ephemeral water bodies (Hann & Loonsberry 1991). Figure 6. On Hardangervidda, the occurrence of Lepidurus arcticus increased significantly with lake size. Lake Tinnhølen (1213 m a.s.l) is a large and shallow lake (4.54 km 2 ) with a high abundance of Lepidurus arcticus and a brown trout population of big-sized fish of excellent quality. Photo: Åsmund Tysse. Branchiopod eggs contain rhodopsin. When activated by water, this pigment reacts to light, stimulating the dormant embryo (Rogers 2014). In notostracan species, hatching is influenced by light, temperature, pH and salinity, as well as by some biotic parameters: nutrients, predators and population density (see Brendonck 1996; Schönbrunner & Eder 2006). Branchiopods are known to produce both dormant and subitaneous embryos (Fryer 1988; Hann & Lonsberry 1991). This adaptation enables eggs to either endure dry or frozen conditions without progressing in development or to continue developing in water based on temperature (Borgstrøm & Larsson 1974). Hatching in L. arcticus normally coincides with the melting of snow and ice break-up, leading to a rapid increase in water temperature followed by an illumination shock to the benthic eggs. From southern Norway, notable examples include larvae found in late June in Lake Stolsvatn (Borgstrøm 1970) and early August in Lake Litlosvatn (Simonsen & Valderhaug 1994), due to the rise in temperature and the illumination shock at ice break-up. Larvae have also been observed as late as August in newly ice-free locations on northern Hardangervidda (Halvorsen 1973). Postembryonic phase: hatch to adult Lepidurus arcticus hatches as a non-feeding nauplius, undergoing a virtual metamorphosis at the first moult (Fryer 1988). It hatches in the lake sediment or among vegetation and possibly does not leave the bottom since it rapidly changes to the second instar, the first larval stage found in plankton samples (Borgstrøm & Larsson 1974). The second instar swims but does not feed because its mandibles are incapable of handling food (Fryer 1988). The third instar is also pelagic, but after these three stages, the larvae become benthic, Qvenild et al .: Lepidurus arcticus in Fennoscandia and the Svalbard Archipelago Fauna norvegica 44: 9–27. 2025 24 Berg OK, Finstad AG, Olsen PH, Arnekleiv JV, Nilssen K. 2010. Dwarfs and cannibals in the Arctic: production of Arctic char (Salvelinus alpinus (L.)) at two trophic levels. Hydrobiologia 652: 337–347. https:// doi.org/10.1007/s10750-010-0366-9 Blomkvist D. 1995. Bladfotingar som försurningsindikatorer i fjällen. Länsstyrelsen i Norrbottens län. Rapport nr. 3-1995. 30 pp. (In Swedish). Borgstrøm R, Garnås E, Saltveit SJ. 1985. Interactions between brown trout, Salmo trutta L., and minnow, Phoxinus phoxinus (L.) for their common prey, Lepidurus arcticus (Pallas). Verhandlungen International Vereinigung für Limnologie 22: 2548–2552. https://doi.org/10.1080/03680770.1983.11897721 Borgstrøm R, Hendrey GR. 1976. pH tolerance of the first larval stages of L. arcticus (Pallas) and adult Gammarus lacustris G.O.Sars. The SNSF-project, Oslo-Ås, Norway. IR 22/76. 37 pp. (In Norwegian with an English summary). Borgstrøm R, Larsson P. 1974. The first three instars of Lepidurus arcticus (Pallas) (Crustacea: Notostraca). Norw. J. Zool. 22: 45–52. Borgstrøm R, Museth J, Brittain JE. 2010. The brown trout (Salmo trutta) in the lake Øvre Heimdalsvatn: long-term changes in population dynamics due to exploitation and the invasive species, European minnow (Phoxinus phoxinus). Hydrobiologia 642: 81–91. https://doi.org/10.1007/s10750-010-0161-7 Borgstrøm R, Aas M, Hegseth H, Dempson JB, Svenning M-A. 2018. Lepidurus arcticus (Crustacea: Notostraca); an unexpected prey of Arctic char (Salvelinus alpinus) in a High Arctic river. Boreal Env. Res. 23: 149–157. Borgstrøm R. 1970. Skjoldkreps, Lepidurus arcticus, i Stolsvannsmagasinet i Hallingdal. Fauna 23: 12–20. (In Norwegian with an English summary). Borgstrøm R. 1973. The effect of increased water level fluctuation upon the brown trout population of Mårvann, a Norwegian reservoir. Norwegian Journal of Zoology 21: 101–112. Borgstrøm R. 2009. Aurebestanden i Skaupsjøen. Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences. Fagrapport fiskeforvaltning i høgfjellet 1 (1): 11 pp. (In Norwegian). Borgstrøm R. 2016. Auren på Hardangervidda er sterkt påverka av klimatilhøve. Naturen nr. 4-2016: 147–155. (In Norwegian). https://doi.org/10.18261/issn.1504-3118-2016-04-02 Borgstrøm R. 2019. Skjoldkreps – eit viktig næringsdyr i høgfjellsvatn som er sterkt påverka av miljøfaktorar. VANN 01-2019: 33–42. (In Norwegian with an English summary). Brabrand Å, Bremnes T, Brittain JE, Saltveit SJ, Gjemlestad L, Haaland S. 2015. En vurdering av virkning på bunndyr og fisk ved økt senkning av Vinstern i Oppland. Naturhistorisk museum, Universitetet i Oslo, Rapport nr. 42, 31 pp. (In Norwegian). Brabrand Å, Saltveit SJ. 1980. Skjoldkreps, Lepidurus arcticus, i Volbufjorden 434 m o.h. i Øystre Slidre, Oppland. Fauna 33: 105–108. (In Norwegian). Brendonck L, Rogers DC, Olesen J, Weeks S, Hoeh WR. 2008. Global diversity of large branchiopods (Crustacea: Branchiopoda) in freshwater. Hydrobiologia 595: 167–176. https://doi.org/10.1007/s10750007-9119-9 Brendonck L. 1996. Diapause, quiescence, hatching requirements: What we can learn from large freshwater branchiopods (Crustacea: Branchiopoda: Anostraca, Notostraca, Conchostraca). Hydrobiologia 320: 85–97. https://doi.org/10.1007/BF00016809 Brittain JE, Borgstrøm R, Bremnes T, Haaland S, Mjelde M, Nilssen JP, Skjelbred B. 2019. Øvre Heimdalsvatn – økologisk langtidsovervåking. Naturhistorisk museum, Universitetet i Oslo, Rapport nr. 84. 64 pp. (In Norwegian with an English summary). Brittain JA, Schartau AK, Svenning M-A. 2020. Biologisk mangfold i ferskvann på Svalbard: kunnskapsgrunnlag, påvirkninger og forslag til framtidig overvåking. Norges vassdragsog energidirektorat. NVE Rapport nr. 13/2020. 97 pp. (In Norwegian). Brtek J, Thiéry A. 1995. The geographic distribution of the European Branchiopods (Anostraca, Notostraca, Spinicaudata, Laevicaudata). Hydrobiologia 298: 263–280. https://doi.org/10.1007/978-94-011-02919_25 Calizza E, Salvatori R, Rossi D, Pasquali V, Careddu G, Sporta Caputi S, Maccapan D, Santarelli L, Montemurro P, Rossi L, Costantini ML. 2022. Climate-related drivers of nutrient inputs and food web structure in shallow Arctic lake ecosystems. Scientific Reports, 12(1), 2125. https://doi.org/10.1038/s41598-022-06136-4 Christoffersen K. 2001. Predation on Daphnia pulex by Lepidurus arcticus. Hydrobiologia 442: 223–229. https://doi.org/10.1023/A:1017584928657 Coulson SJ, Convey P, Aakra K, Aarvik LL, Ávila-Jiménez ML, Babenko A, Biersma EM, Bostrom S, Brittain JE, Carlsson AM, Christoffersen KS, de Smet WH, Ekrem T, Fjellberg A, Füreder L, Gustafsson DR, Gwiazdowicz DJ, Hansen LO, Holmstrup M, Hullé M, Kaczmarek L, Kolicka M, Kuklin VV, Lakka H-K, Lebedeva N, Makarova OL, Maraldo K, Melekhina EN, Ødegaard F, Pilskog HE, Simon JC, Sohlenius B, Solhøy T, Søli GEE, Stur E, Tanasevitch AV, Taskaeva AA, Velle G, Zawierucha K, Zmudczyńska-Skarbek K. 2014. The terrestrial and freshwater invertebrate biodiversity of the archipelagoes of the Barents Sea; Svalbard, Franz Josef land and Novaya Zemlya. Soil Biology & Biochemistry 68, 440–470. https://doi.org/10.1016/j. soilbio.2013.10.006 Dahl K. 1932. Influence of water storage of food conditions on trout in Lake Paalsbufjord. Skrifter utgitt av Det Norske Videnskaps-Akademi i Oslo. I. Mat.-Naturv. Klasse. 1931. No. 4. 53 pp. Dahl K. 1933. Vassdragsreguleringers virkninger på fisket i innsjøer. J. W. Cappelens forlag, Oslo. (In Norwegian). Dahl SO, Nesje A. 1996. A new approach to calculating Holocene winter precipitation by combining glacier equilibrium-line altitudes and pine-tree limits: a case study from Hardangerjøkulen, central southern Norway. The Holocene 6, 4: 381–398. https://doi. org/10.1177/095968369600600401 Dimante-Deimantovica I, Chertoprud M, Chertoprud E, Christoffersen KS, Novichkova A, Walseng B. 2015. FREMONEC: Effect of climate change and related stressors on fresh and brackish water ecosystems in Svalbard. A Norwegian and Russian joint scientific project. Norwegian Institute for Nature Research (NINA). Report 1218. 40 pp. http://hdl. handle.net/11250/2380592 Dimante-Deimantovica I, Walseng B, Chertoprud ES, Novichkova A. 2018. New and previously known species of Copepoda and Cladocera (Crustacea) from Svalbard, Norway – who are they and where do they come from? Fauna norvegica 38: 18–29. https://doi/10.5324/ fn.v38i0.2502 Dolmans V, Partoens L, Deboelpaep E, Horváth Z, Vanschoenwinkel B. 2025. Dietary data suggest large branchiopods may be an underrecognised food resource for a wide range of waterbirds. Hydrobiologia: 1–17. https://doi.org/10.1007/s10750-025-05810-8 Ebne I. 2009. Anadrom røye (Salvelinus alpinus) i Linnévassdraget, Svalbard; Diett, oppvandring, bestandssammensetning og fangbarhet. MSc thesis, University of Life Sciences, Ås. 64 pp. (In Norwegian). Eiríksson Þ, Þorleifsdóttir Þ, Sigurjónsdóttir H, Malmquist HJ. 2021. Huldudýr á heiðum uppi– útbreiðsla skötuorms á Íslandi. Náttúrufræðingurinn 91 (3–4): 146–165. (A rare animal in the Iceland Highland – the Arctic tadpole shrimp). (In Icelandic). https://rorum.is/files/skra/63/ Enge E, Qvenild T, Hesthagen T. 2017. Fish death in mountain lakes in southwestern Norway during 1800s and early 1900s – a review of historical data. Vann nr. 1-2017: 66–80. Evenseth A, Christensen G, Kallenborn R. 2005. Selected chlorobornanes, polychlorinated naphthalenes and brominated flame retardants in Bjørnøya (Bear Island) freshwater. Environmental Pollution 136: 419–430. https://doi.org/10.1016/j.envpol.2005.01.018 Fjellheim A. 2004. Virkning av rotenonbehandling på bunndyrsamfunnene i et område ved Stigstu, Hardangervidda. Lab. Ferskv. Økol. Innlandsfiske. LFI-UNIFOB. Universitet i Bergen. Rapport nr. 122. 60 pp. (In Norwegian). Qvenild et al .: Lepidurus arcticus in Fennoscandia and the Svalbard Archipelago Fauna norvegica 44: 9–27. 2025 25 Fjellheim A, Tysse Å, Bjerknes V, Wright RF. 2002. Finprikkauren på Hardangervidda. DN-utredning 2002-1. 58 pp. (In Norwegian). Fjellheim A, Tysse Å, Bjerknes W. 2007. Fish Stomachs as a Biomonitoring Tool in Studies of Invertebrate Recovery. Water, Air and Soil Pollution 7: 293–300. https://doi.org/10.1007/s11267-006-9074-x Fryer G. 1988. Studies on the functional morphology and biology of the Notostraca (Crustacea: Branchiopoda). Philosophical Transactions of the Royal Society B. Vol. 321: 27–124. https://doi.org/10.1098/ rstb.1988.0091 Fryer G. 1996. Diapause, a potent force in the evolution of freshwater crustaceans. Hydrobologia 320: 1–14. https://doi.org/10.1007/ BF00016800 Geyer G, Hegna TA, Kelber KP. 2024. The end of the ‘living fossil’ tale? A new look at Triassic specimens assigned to the tadpole shrimp Triops cancriformis (Notostraca) and associated phyllopods from the Vosges region (eastern France). Papers in Palaeontology, Vol. 10, Part 5, e1589. https://doi.org/10.1002/spp2.1589 Gillooly JF, Dodson SI. 2000. The relationship of neonate mass and incubation temperature to embryonic development in a range of animal taxa. Journal of Zoology 251: 369–375. https://doi. org/10.1111/j.1469-7998.2000.tb01087.x Halvorsen G. 1973. Crustacea from the High Mountain Area Hardangervidda, South Norway. Rapport fra Høyfjellsøkologisk Forskningssenter, Finse, Norge. 1973 (3). 17 pp. Hann BJ, Lonsberry B. 1991. Influence of temperature on hatching of eggs of Lepidurus couesii (Crustacea, Notostraca). Hydrobiologia, 212: 61–66. https://doi.org/10.1007/BF00025987 Hanssen-Bauer I, Førland EJ, Hisdal H, Mayer S, Sandø AB, Sorteberg A. (Editors). 2019. Climate in Svalbard 2100 – a knowledge base for climate adaptation. Norwegian Environment Agency (Miljødirektoratet), Report 1/2019. 207 pp. Hessen D, Rueness EK, Stabell M. 2004. Circumpolar analysis of morphological and genetic diversity in the Notostracan Lepidurus arcticus. Hydrobiologia 519: 73–84. https://doi.org/10.1023/ B:HYDR.0000026486.16615.06 Hesthagen T, Gran R. 2019. Auren i Vinstre-magasinet: bestandstilhøve, fangst og utsettingar gjennom 40 år. Norwegian Institute for Nature Research (NINA). Report 1637. 53 pp. (In Norwegian). Hesthagen T. 1979. Utbredelse av skjoldkreps Lepidurus arcticus i Lom kommune, Oppland. Fauna 33: 30–33. (In Norwegian). Hesthagen T. 2018. Fangstutbyte og bestandstilhøva hjå auren i Aursjøenmagasinet i Skjåk kommune i søraustlege delen av Reinheimen i åra 1980–2017. Norwegian Institute for Nature Research (NINA). Report 1446. 35 pp. (In Norwegian). Hesthagen T. 2022. Draggarnfisking i Gudbrandsdalen. Årbok for Gudbrandsdalen 90: 157–176. (In Norwegian). Hesthagen T. 2005. Sylvetjønne – eit fiskevatn utanom det vanlege. Heim og bygd 13: 68–81. (In Norwegian). Huitfeldt-Kaas H. 1911. Indberetning om Fiskeriforholdene paa Hardangervidden. I: Indstilling fra Fjeldbeitekomiteen om Harangviddens Utnyttelse. Landbruksdepartementet. (Centraltrykkeriet, Kristiania). 106 pp. (In Norwegian). Huitfeldt-Kaas H. 1935. Der Einfluss der Gewässerregelungen auf den Fischbestand in Binnenseen. Oslo. 105 pp. (In Deutsh). Håland A. 2012. Numbers, density and trends of breeding Black Scoters Melanitta n. nigra at the Hardangervidda plateau, southern Norway 1978–2012, in perspective of climate variations and varying density of Brown Trout Salmo trutta. Ornithology Studies 2012-1: 1–15. Janiec K. 1996. The comparison of freshwater invertebrates of Spitsbergen (Arctic) and King George Island (Antarctic). Polish Polar Research 17 (3–4): 173–202. Jeppesen E, Christoffersen K, Landkildehus F, Lauridsen T, Amsinck SL, Riget F, Søndergaard M. 2001. Fish and crustaceans in northeast Greenland lakes with special emphasis on interactions between Arctic char (Salvelinus alpinus), Lepidurus arcticus and benthic chydorids. Hydrobiologia 442: 329–337. https://doi.org/10.1023/A:1017508211819 Jeuthe H, Brännäs E, Nilsson J. 2016. Effects of variable egg incubation temperatures on the embryonic development in Arctic charr Salvelinus alpinus. Aquaculture Research, 47(12): 3753–3764. https://doi. org/10.1111/are.12825 Jørgensen I, Eie JA. 1993. Utbredelsen av fisk, bunndyr og fisk i innsjøer og dammer på Mosselhalvøya, Svalbard. Norwegian Institute for Nature Research (NINA). Research report 45. 25 pp. (In Norwegian). Järvinen A, Lakka H-K, Sujala M. 2014. Arktinen Kilpikidusjalkainen, tunturivesien elävä fossiili, löydetty jälleen Suomesta. (The living fossil Arctic tadpole shrimp was found again in Finland). Luonnon Tutkija, 1: 19–24. (In Finnish). Klausen TR. 2012. Population regulation in the tadpole shrimp Lepidurus arcticus. MSc-thesis, Norwegian University of Science and Technology, Department of Biology. 25 pp. http://hdl.handle.net/11250/245161 Klemetsen A, Grotnes PE, Holthe H, Kristoffersen K. 1985. Bear Island Charr. Report, Inst. Freshw. Res., Drottningholm, 62: 98–119. Koli L. 1957. Beiträge zur Kenntnis der Euphyllopodenfauna Finnlands. Archiv Societatis Zoologicae Botanicae Fennica ‘Vanamo’. 11, 2: 108–111. (In Deutsch). Koops MA, Tallman RF. 2004. Adaptive variation in the development and mortality of Arctic char eggs. In Physiology of Fish Eggs and Larvae: Proc. Symp. Int. Congr. Biol. Fish, Manaus, Brazil, 1: 47–68. Kuller Z, Gasith A. 1996. Comparison of the hatching process of the tadpole shrimps Triops cancriformis and Lepidurus apus lubbocki (Notostraca) and its relation to their distribution in rain-pools in Israel. Hydrobiologia 335: 147–157. https://doi.org/10.1007/BF00015276 Lakka H-K, Eloranta AP, Hesthagen T, Saksgård R, Power M. 2020. Impacts of reduced Lepidurus arcticus availability on brown trout life history traits in a mountain reservoir. Aquatic Sciences 82:78. 11 pp. https://doi.org/10.1007/s00027-020-00751-x Lakka H-K. 2013. The ecology of a freshwater crustacean: Lepidurus arcticus (Branchiopoda, Notostraca) in a high Arctic region. The University Centre in Svalbard, Department of High Arctic Biology. MSc thesis. The University Centre in Svalbard/ University of Helsinki. 151 pp. http://hdl.handle.net/10138/41586 Lakka H-K. 2015. Description of the male Lepidurus arcticus (Branchiopoda: Notostraca) and the potential role of cannibalism in defining male form and population sex ratio. Journal of Crustacean Biology 35(3): 319–329. https://doi.org/10.1163/1937240X-00002324 Lakka H-K. 2020. Environmental Changes in Arctic Freshwaters. The Response of Indicator Species to Global Warming and Acidification in the Arctic. PhD-thesis, University of Jyväskylä, 2020: 51 pp. https:// jyx.jyu.fi/jyx/Record/jyx_123456789_72134 Lakka H-K. 2021. Haussa tunturivesien äyriäisiä – ilmoita havaintosi! (Looking for crustaceans from mountain waters – report your observations). Suomen Luonto. (In Finnish). Lehmann GB, Gabrielsen S-E, Wiers T, Sandven OR. 2008. Fiskeribiologiske undersøkelser i Halnefjorden, Store og Vesle Krækkja, Krækjungen, Heinungen og Øvre og Nedre Hein august 2007. LFI-Unifob. Report 152. 62 pp. (In Norwegian). Lien L. 1978. The energy budget of the brown trout population of Øvre Heimdalsvatn. Holarctic Ecology 1: 279–300. https://doi. org/10.1111/j.1600-0587.1978.tb00963.x Lindholm M, Hessen DO, Færøvig PJ, Rognerud B, Andersen T, Stordal F. 2015. Is distribution of cold stenotherms constrained by temperature? The case of the Arctic fairy shrimp (Branchinecta palludosa O.F.Müller 1788). Journal of Thermal Biology 53: 46–52. https://doi.org/10.1016/j.jtherbio.2015.08.005 Lingdell P-E, Engblom E. 2002. Bottendjur som indikator på kalkningseffekter. Report 5235, Naturvårdsverket. 191 pp. (In Swedish). Longhurst AR. 1955. Evolution in the Notostraca. Evolution 9: 84–86. https://doi.org/10.2307/2405360 Luoto T, Oksman M, Ojala AEK. 2016. Invertebrate communities of the High Arctic ponds in Hornsund. Polish Polar Research, 37(1): 105–119. https://doi.org/10.1515/popore-2016-0003 Qvenild et al .: Lepidurus arcticus in Fennoscandia and the Svalbard Archipelago Fauna norvegica 44: 9–27. 2025 26 Mancinelli G, Pasquali V. 2016. Body size-related constraints on the movement behaviour of the arctic notostracan Lepidurus arcticus (Pallas, 1793) under laboratory conditions. Environment changes in Arctic. https://doi.org/10.1007/s12210-016-0512-z Miller MC. 1980. Tadpole shrimp. In Hobbie, J.E (ed.). Limnology of Tundra Ponds. Barrow, Alaska. US/IBP Synthesis Series 13: 323–335. Mitchell GF. 1957. Late-glacial finds of Lepidurus arcticus (Pallas) in the British Isles. Nature 180: 153. https://doi.org/10.1038/180513a0 Møller OS, Olesen J, Høeg JT. 2003. SEM studies on the early larval development of Triops cancriformis (Bosc) (Crustacea: Branchiopoda, Notostraca). Acta Zoologica 84: 267–284. https://doi.org/10.1046/ j.1463-6395.2003.00146.x Museth J, Hesthagen T, Sandlund OT, Thorstad EB, Ugedal O. 2007. The history of the minnow Phoxinus phoxinus (L.) in Norway: from harmless species to pest. Journal of Fish Biology 71 (Supplement D): 184–195. https://doi.org/10.1111/j.1095-8649.2007.01673.x Neretina AN, Gololobova MA, Neplyukhina AA, Zharov AA, Rogers CD, Horne DJ, Protopopov AV, Kotov AA. 2020. Crustacean remains from the Yuka mammoth raise questions about non-analogue freshwater communities in the Beringian region during the Pleistocene. Sci. Report 10, 859. https://doi.org/10.1038/s41598-020-57604-8 Nowiński K, Wiśniewska-Wojtasik B. 2006. Diversity of abiotic properties of water in shallow lakes in Hornsund area (SW Spitsbergen). Limnological Review 6: 215–222. OʼBrien SM, Helm B. 2025. First record of Lepidurus lemmoni (Holmes 1894) (Crustacea: Notostraca) in Californiaʼs Central Valley. California Fish and Wildlife journal, 111, e1. https://doi.org/10.51492/cfwj.111.1 Olofsson O. 1918. Studien über die Süsswasserfauna Spitzbergens. Beitrag zur Systematik, Biologie und Thiergeographie der Crustaceen und Rotatorien. Zoologiska Bidrag från Uppsala, Bd 6. 468 pp. (In German). Pasquali V, Calizza E, Setini A, Hazzlerigg D, Christoffersen KS. 2019. Preliminary observations on the effect of light and temperature on the hatching success and rate of Lepidurus arcticus eggs. Ethology, Ecology & Evolution 31–4: 348–357. https://doi.org/10.1080/0394937 0.2019.1609093 Pedersen K, Scobie L. 1990. Dynamikk, habitatbruk og redskapsseleksjon for ørretbestanden i Kollsvatn, en innsjø på Hardangervidda. MSc thesis, University of Life Sciences, Ås. 59 pp. (In Norwegian). Presthus Heggen M, Birks HH, Anderson NJ. 2010. Long-term ecosystem dynamics of a small lake and its catchment in west Greenland. The Holocene 20(8): 1207–1222. https://doi.org/10.1177/0959683610371995 Qvenild T, Fjeld E, Fjellheim A, Hammar J, Hesthagen T, Lakka H-K. 2021. Upper thermal threshold of Lepidurus arcticus (Branchiopoda, Notostraca) in lakes on the southern outreach of its distribution range. Fauna norvegica 41: 50–88. https://doi.org/10.5324/fn.v41i0.3832 Qvenild T, Fjeld E, Fjellheim A, Hesthagen T, Lakka H-K, Rognerud S, Tysse Å. 2021. Ørretens viktigste næringsdyr på Hardangervidda. NATUREN nr. 4: 202–212. (In Norwegian). https://doi.org/10.18261/ issn.1504-3118-2021-04-06 Qvenild T, Fjeld E, Fjellheim A, Rognerud S, Tysse Å. 2018. Climatic effects on a cold stenotherm species Lepidurus arcticus (Branchiopoda, Notostraca) on the southern outreach of its distribution range. Fauna norvegica 38: 37–53. https://doi.org/10.5324/fn.v38i0.2598 Qvenild T, Hesthagen T, Museth J. 2024. A long-term study of the impact of the invasive species Eurasian minnow Phoxinus phoxinus, on brown trout Salmo trutta production in a high mountain lake, Southern Norway. Fauna norvegica 43: 1–11. https://doi.org/10.5324/ fn.v43i0.5826 Qvenild T, Hesthagen T. 2019. Environmental conditions limit the distribution of Lepidurus arcticus (Branchiopoda, Notostraca) on the Hardangervidda mountain plateau, Southern Norway. Fauna norvegica 39: 77–110. https://doi.org/10.5324/fn.v39i0.2687 Qvenild T, Hesthagen T. 2020. The viability of the crustacean Eurycercus lamellatus (Branciopoda, Cladocera) in a high mountain area in southern Norway. Fauna norvegica 40: 22–42. https://doi.org/10.5324/ fn.v40i0.3340 Qvenild T. 2022. Climatic impact on the crustacean species Lepidurus arcticus, Gammarus lacustris and Eurycercus lamellatus on brown trout Salmo trutta production in a high mountain area in Southern Norway. Doctoral thesis, Faculty of Mathematics and Natural Sciences, University in Oslo. 227 pp. http://urn.nb.no/URN:NBN:no-93328 Røen UI. 1962. Studies on Freshwater Entomostraca in Greenland. II. Locations, Ecology and Geographical Distribution of the Species. Meddelser om Grønland, Bd. 170, No. 2. 149 pp. Rogacki M, Brysiewicz A. 2021. Tadpole shrimps – A general review of the little known crustaceans of ephemeral waterbodies. Research in Ecology, Vol. 03(02): 18–24. https://doi.org/10.30564/re.v3i2.2910 Rogers DC. 2001. Revision of the Nearctic Lepidurus (Notostraca). Journal of crustacean biology, 21(4): 991–1006. https://doi. org/10.1163/20021975-99990192 Rogers DC. 2014. Larger hatching fractions in avian dispersed anostracan eggs (Branchiopoda). Journal of Crustacean Biology. 34(2): 135–143. https://doi.org/10.1163/1937240X-00002220 Rogers DC, Zharov AA, Neretina AN, Kuzmina SA, Kotov AA. 2021. A Review of Recently Discovered Remains of the Pleistocene Branchiopods (Anostraca, Notostraca) from NE Siberia and Arctic Canada. Water 13, 280. https://doi.org/10.3390/w13030280 Rognerud S, Borgstrøm R, Qvenild T, Tysse Å. 2003. Ørreten på Hardangervidda. Norwegian Institute for Water Research (NIVA), Report L.NR. 4712–2003. 68 pp. (In Norwegian). Rognerud S, Fjeld E. 2014. Undersøkelser av fisk og næringsdyr i Mår og Ringedalsvatnet 2011–2013. Norwegian Institute for Water Research (NIVA), Report L.NR. 6682-2014. 52 pp. (In Norwegian). Rukke NA. 2002. Effects of low calcium concentrations on two common freshwater crustaceans, Gammarus lacustris and Astacus astacus. Freshwater Ecology 16: 357–366. https://doi.org/10.1046/j.13652435.2002.00637.x Sars GO. 1864. Beretning om en i Sommeren 1863 foretagen zoologisk reise i Christiania Stift. Nyt Mag. Naturvid. 13: 225–260. Sayenko E, Minakawa N. 1999. Occurrence of two crustacean species, Branchinecta palludosa (O.F. Müller, 1788) (Anostraca) and Lepidurus arcticus (Pallas, 1793) (Notostraca), on the Kuril Archipelago. Crustaceana 72(7): 710–712. Scher O, Defaye D, Korovchinsky NM, Thiéry A. 2000. The Crustacean fauna (Branchiopoda, Copepoda) of shallow freshwater bodies in Iceland. Vestnik zoologii, 34(6): 11–25. Schönbrunner IM, Eder E. 2006. pH-related hatching success of Triops cancriformis (Crustacea: Branchiopoda: Notostraca). Hydrobiologia. 563: 515–520. https://doi.org/10.1007/s10750-006-0018-2 Simonsen TA, Valderhaug NA. 1994. Bestandsdynamikk, habitatbruk og ernæring for aure i Litlosvatn – en innsjø på Hardangervidda. MSc thesis, University of Life Sciences, Ås. 65 pp. (In Norwegian). Sømme S. 1934. Contributions to the biology of Norwegian fish food animals. I. Lepidurus arcticus Pallas. Avh. Norske Vidensk Akad 6: 1–36. Summerhayes VS, Elton CS. 1923. Contributions to the ecology of Spitzbergen and Bear Island. Journal of Ecology 11: 214–286. Svenning M-A. 2015. Miljøvariable i innsjøer på Svalbard; vanntemperatur, lysog isforhold. Norwegian Institute for Nature Research (NINA). Minireport 575. 37 pp. (In Norwegian). Thiéry A. 1997. Horizontal distribution and abundance of cysts of several large branchiopods in temporary pool and ditch sediments. Hydrobiologia, 259: 177–189. doi.org/10.1023/A:1003124617897 Thor SA. 1930. Beiträge zur Kenntnis der Invertebraten Fauna von Svalbard. Skrifter om Svalbard og Ishavet nr. 27. 145 pp. (In Deutsch). Tysse Å, Fjellheim A, Stakseng H, Gåsdal O, Aasland E, Elnan G. 2022. Finprikkauren på Hardangervidda. Årsrapport 2022. 19 pp. (In Norwegian). Vanschoenwinkel B, Pinceel T, Vanhove MPM, Denis C, Jocque M, Timms BV, Brendonck L. 2012. Toward a global phylogeny of the «living fossil» crustacean order Notostraca. PLoS One, 7, e34998. https://doi.org/10.1371/journal.pone.0034998 Qvenild et al .: Lepidurus arcticus in Fennoscandia and the Svalbard Archipelago Fauna norvegica 44: 9–27. 2025 27 Vekhoff NV. 1997. Large branchiopod Crustacea (Anostraca, Notostraca, Spinicaudata) of the Barents region of Russia. Hydrobiologia 359: 69–74. https://doi.org/10.1023/A:1003116432010 Walseng B, Raddum G, Saksgård R, Schartau AKL. 1996. Ferskvannsbiologiske undersøkelser i Kvenna 1995, med fokus på indikatorarter som redskap i forsuringsovervåkingen. Norwegian Institute for Nature Research (NINA). Oppdragsmelding 433. 36 pp. (In Norwegian). Walseng B, Jensen T, Dimante-Deimantovica I, Christofersen KS, Chertoprud M, Chertoprud E, Novichkova A, Hessen DO. 2018. Freshwater diversity in Svalbard: providing baseline data for ecosystems in change. Polar Biology 41: 1995–2005. https://doi. org/10.1007/s00300-018-2340-3 Wojtasik B, Brylka-Wolk M. 2010. Reproduction and genetic structure of a freshwater crustacean Lepidurus arcticus from Spitsbergen. Polish Polar Research 31 (1): 33–44. https://doi.org/10.4202:ppres.2010.03 Økland KA, Økland J. 2003. Skjoldkrepsen Lepidurus arcticus i Norge. Fauna nr. 1-2003: 2–12. (In Norwegian with an English summary). Editorial responsibility: Anne Helene Tandberg. This article is open-access and distributed under the terms of the Creative Commons Attribution 4.0 International license. This permits all noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. (http://creativecommons.org/licenses/by/4.0/).