RELICT SETTLEMENT OF THE CHITON LEPIDOCHITONA-CINEREA (MOLLUSCA, POLYPLACOPHORA) IN NORTHERN NORWAY

The subtropical low-boreal chiton Lepidochitona cinerea (L., 1767) was found in intertidal pools on Tromso Island in northern Norway. Althou gh remote fi-om the main part of the species distribution range, the p opulation appears to be safe, with a regular annual recruitment. It is thought that L. cinerea invaded northern Norwegian waters during a pe riod of warming, either 5 to 6 millennia or possibly just. one millenn ium ago. Subsequent cooling destroyed the constant settlement of this rather warm water species in the open parts of fjords. Small populatio ns of L. cinerea that remained in the intertidal pools could persist d ue to the species tolerance for severe winter temperatures, as well as the considerable warming of water in the pools during the prolonged l ow tides in summer. The summer warming of water allows the chitons not only to mature, but also to spawn. Some planktonic larvae may escape from intertidal pools into open waters, where they may survive, but ap parently do not spawn. Besides L. cinerea, other chiton species, the h igh-boreal Tonicella rubra (L., 1767), as well as the boreal-arctic T. marmorea (Fabricius, 1780) and Stenosemus albus (L., 1767), were foun d in the same intertidal pools, possibly having arrived there as a res ult of storms.