Southwards migration of freshwater invertebrates from northern Norway
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Abstract
Remains of larvae of caddis flies (Insecta, Trichoptera) and non-biting midges (Insecta, Chironomidae) were recorded in core samples dated at 12 000 – 11 000 and about 20 000 B.P., respectively, from lakes on Andøya, Norway (69º15'N). All caddis remains belonged to Apatania zonella (Zetterstedt). 4 Orthocladinae species, Pseudodiamesa sp., Metriocnemus obscuripes (Holmgren), Sp. A and Sp. B (Ortocladius sp.?) were found.
Fragments of a crustacean, Lepidurus arcticus Krøyer, were present in sediments dated to ca 12 800 B.P.
Ice-free areas and lotic/lentic (running/standing water) habitats have been present on Andøya at least from ca 22 000 B.P. Of insects, chironomids must have been one of the earliest colonizers of freshwater habitats, and we suggest that A. zonella was the first arctic/alpine caddis species to colonize Norway after the last ice age.
The existence of an ice-free coastal refugium, from at least 22 000 B.P. on Andøya, strongly suggest an early southwards migration of arctic/alpine aquatic and terrestrial invertebrates from this area through Norway and Sweden, in addition to immigration from the south and east during and after the deglaciation.
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