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