Too old to be new? A recent discovery of a pteropod Limacina lesueurii (d'Orbigny 1836) at the Swedish west coast (Skagerrak, North Sea)

The pteropod Limacina lesueurii (d'Orbigny 1836) is a subtropical species, which in the Atlantic Ocean shows maximum abundance between 30°N and 25°S. In the North Sea, this species has so far only been occasionally reported from the coastal waters off the northern Scotland and in the English Channel. In this short note, we for the first time report presence of L. lesueurii in two sediment cores taken in the Kosterfjord (Skagerrak, North Sea). The pteropod, generally absent or occurring in low numbers throughout both cores, showed distinctly higher abundances between 100 and 130 cm core depth, which based on dating by ¹³⁷Cs, ²¹⁰Pb and lead pollution records corresponds to ~1920–1950s. During this period positive sea surface temperature anomalies were reported in the North Atlantic and number of oceanic water inflows have been documented for the North Sea. Some of these inflows were accompanied by ”enormous shoals” of L. lesueurii observed in the English Channel and NE of Scotland. We hypothesize that L. lesueurii was transported into the Skagerrak in connection with these and propose this pteropod species as a new valuable stratigraphic marker for oceanic water inflows in the study area.