The earliest notification of climatic changes affecting seaweed distribution was published by the late Peter Dixon (Biol.Signif.Clim.Changes in Britain: 113. 1965), where temperature is postulated to be the cause of recent re-invasions in Europe, and there are several examples in Scandinavian waters. Apart from those mentioned by Dixon, the warm-temperate red alga Sphaerococcus coronopifolius Stackhouse is presently considered to be an established species in Sweden - the first confirmed records dating since the 90's (and unconfirmed ones suggesting conspecifity with Lyngbye's Desmia hornemanii described in 1819 from Oeresund). Several European Delesseriaceae such as Hypoglossum Kuetzing and Haraldiophyllum Zinova are new members of the Scandinavian flora since a few decades. The possibility that such southern species could be in fact glacial survivals exists but is remote. If so, we would expect to see endemics as well - but to find the latter we have to 'botanize' along the maximum ice cover, apparently both in the south and the northern border of the latest glaciation (Nord.J.Bot.24: 469-499. 2007; Taxon 57: 223-230. 2008).
Yet, the case of Fucus evanescens C. Agardh 1820 stands as unique. Here we have a supposed Arctic species that in the past 100 years expanded its distribution in the opposite direction. Until 1890, its southern limit was near the polar circle (Kjellman, Handb.Skand.havsalgfl.: 67. 1890), but in 1894 it was reported from Oslofjord - a 'natural' jump of about 7°. Within 30 years it had reached the Swedish west coast, and after another 70 years it was recorded in Kiel's Bay (nearly 12° below the polar circle). The arctic-like conditions of the Baltic might explain this event, but the species was also reported from the Faeroes (Boergesen, Mar.Alg.Faeroes: 465. 1902, as F. inflatus) and the Shetlands (Powell in J.mar.bio.Assoc.U.K.36: 664-5. 1957, as subsp. edentatus). Recently, Baltic hybrids with local F. serratus Linne have been reported - although the two species coexist for thousands of years above the polar circle. It was hypothesized that local hybridization could be due to differences between the (isolated) Baltic F. serratus and the polar populations (Proc.R.Soc.Lond.269: 1829-34. 2002), but was that F. evanescens the same species originally described from Kamtchatka, genetically more related to F. gardneri Silva from the North Pacific (J.phycol.35: 389. 1999), and currently 'synonymized' with F. inflatus Linne 1753 (type locality: Norway), F. edentatus Pylaie 1829 (type locality: New Foundland), and F. bursigerus J. Agardh 1868 (type locality: Spitsbergen) ?
A few months ago, several Fucus specimens surfaced unexpectedly in a closet. They were sent away from a herbarium, thankfully not thrown away without consultation. A closer look showed that they were collected by D. Hylmoe at Varberg, on the Swedish west coast, between February 1933 and April 1934. Lenghty comments on the labels such as 'Fucus serratus L. x inflatus..', 'Fucus inflatus L. x vesiculosus...', '...x...', '...x...', '...x...', '...x...', reveal a burning interest and intensive effort to find out. They were given a place as the first collections of an introduced species in that part of Sweden, deserving thorougher attention.
Was it the Arctic seaweed ?
with best wishes for the Holidays and the New Year,
and a reminder of the field courses the coming summer
Dr. A. Athanasiadis
University of Gothenburg
P.O. Box 461
SE 405 30 Gothenburg, Sweden