seaweed biogeography and Aulin's contribution

Algologia algologia at TELIA.COM
Mon Dec 18 21:41:22 CST 2000


With an age of nearly 175 years, seaweed biogeography has much to
celebrate. It started in 1826 with Lamouroux' 'Memoire sur la Geographie
des plantes marines' that remains remarkable. Lamouroux predicted that
algae could grow down to 100-200 fathoms and that species in the tropics at
such depths (where temps are 4-5 C) should be able to extent in cold waters
(see corallines). Following de Candolle, he divided the hydrophytes in 12
groups according to position on the shore, and also described the
latitudinal range of his 5 classes (Fucacees, Floridees, Dictyotees,
Ulvacees and Conferves) and their 'principaux' genera.
       In 1844, Oersted proposed the theory of chromatic adaptation to
explain the apparent green-brown-red algal zonation - it persisted until
the end of the 18th century.
        Harvey (Nereis. 1852) was probably the first to recognize algal
regions describing the seaweed distribution in the NE Atlantic - a model
later adopted by Martens ('Die Tange'. 1866) and many others.
        With Aulin's 'Anteckningar oefver Hafsalgernas geografiska
utbredning...' in 1872, ends the first period - biogeography now swifts to
ecological and phytosociological aspects.
        Classical works of the new period make a part of floristic
investigations such as of Kjellman (The Algae of the Arctic Sea. 1883),
Boergesen (The Marine Algae of the Faeroes. 1902; The Algae-vegetation of
the Faeroese coasts. 1905), Hoyt (Marine Algae of Beaufort, N.C. 1920),
Feldmann ('Recherches sur la vegetation marine de la Mediterranee'. 1937;
'Les algues marines de la cote des Alberes'. 1937-42), Skottsberg
(Communities of marine algae in Subantarctic and Antarctic waters. 1941,
and many others).
        Yet, the seeds of historical biogeography were planted by Kjellman
(l. c.) and Murray (A comparison of the Marine Floras of the warm Atlantic,
Indian Ocean, and the Cape of Good Hope. 1893). Kjellman suggested that
'... the occurrence of several algae in the northern Atlantic at the same
time as in the Pacific may probably be explained by the former distribution
of water and land and the different physical conditions of the seas in
former times...', and Murray that climatic changes in past geological time
may explain the present close relationship between disjunct algal floras.
        Studying the genus Caulerpa and the theories of Duncan, Hill,
Ortmann, and Nathorst on the geological history of the Isthmus of Panama
(published between 1863 and 1902), Svedelius ('Om likheten mellan
Västindiens samt Indiska och Stilla Oceanens marina vegetation'. 1906)
proposed that the close relationship between the Caribbean and the
Indo-Pacific floras stems from a continuous marine vegetation from the
Tertiary and 16 years later confirmed his postulation in light of Wegener's
and Vaughan's findings (Svedelius: On the discontinuous geographical
distribution of some tropical and subtropical marine algae. 1924).
       Svedelius' thesis reflects a purely cladistic thinking in analysing
relationships within monophyletic groups (concepts such as centre of
distribution and sister-taxon relationships are consistently used for the
first time as far as systematic knowledge permits). For example, with
regard to the biogeography of Scinaia (based on Setchell's account from
1914), Svedelius maintains '...that the Atlantic species are not most
nearly allied to the species from the Cape....[but] Sc. furcellata belongs
to the same group as the Pacific Sc. Johnstoniae...from California and Sc.
japonica ...from Japan [while T]he species from the Cape has its most
nearly related species at Ceylon, Philippine Islands, Hawaii, and
California.]' and continues that 'if...we suppose that the connection was
over the isthmus...[T]he fact that the Atlantic species have their most
nearly related species at about the same latitude in the Pacific will be
more easily explained...'.
        With regard to the occurrence of Anadyomene stellata in the
Mediterranean, he marks that '[t]he question now arises if [this species
has] immigrated into the Mediterranean from the Atlantic, that is, from the
west, or from any other direction ? As the species is not known from the
Red Sea, immigration in later times through the Suez canal need not be
discussed. Moreover, the species... was observed in the Mediterranean
before the opening of that canal. In spite of this, the species may still
have got into the Mediterranean from the east...during an early epoch when
this sea had open connection with the Indian-Pacific Ocean during Tertiary
times....'.
        In the 2nd half of the 20th century, we would expect the growth of
systematics to promote biogeography in Svedelius' lines, but this does not
happen. Instead, seaweed biogeography becomes largely synonymous with the
concept of 'algal provinces'. Twenty-two such regions are treated as
natural units being correlated to temperature and salinity gradients.
Degrees of continuity-discontinuity between regions are calculated on the
basis of taxonomic similarity, and while the concept of monophyly and
phylogenetic classification seem to be forgotten, we advance biogeographic
scenarios strictly on the basis of phenetics (see e.g. Botanica mar. 29.
1986). A critique to this monolithic approach appeared in 1987 (Helgol.
Meeres. 41: 235-244. 1987), followed by the first paper on phylogenetic
(cladistic or vicariance) algal biogeography (in the same journal) and an
introduction to the theory of phylogenetic systematics for phycology (J.
Phycol. 25: 407-411. 1989). Since then, cladistic thinking has gained
further support (see NATO ASI Series G Ecol. Sci. 22. 1989; J. Phycol. 30:
67-90. 1994;  Botanica mar. 37: 193-203. 1994; J. Phycol. 31: 644-655.
1995; Opera Bot. 128. 1996; J. Phycol. 35: 382-394. 1999) - to be seen as a
sign of creative work using more approaches in the field of biogeography.
        As an epilogue, I turn to Aulin's contribution that was a unique
synthesis for its time and a step towards the application of a systematic
model to the understanding of seaweed distribution.

Algologia has the pleasure to offer a translation of Aulin's thesis at
http://w1.311.telia.com/~u31101877

with best wishes for Christmas and the New Year

                                      ALGOLOGIA
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