Biology Reference
In-Depth Information
Chapter 13
Seaweeds and Their Communities in Polar
Regions
Christian Wiencke and Charles D. Amsler
13.1
Introduction
The natural environment of polar seaweeds is characterized by strong seasonal light
conditions and constant low temperatures (Zacher et al.
2011
). At the northern and
southern distribution limits of seaweeds in the Arctic (80
N) and Antarctic (77
S),
the polar night lasts for about 4 months. At lower latitudes, e.g., the northern border
of the Antarctic region, at King George Island (South Shetland Islands; 62
S)
daylength varies between 20 h in summer and 5 h in winter. Sea-ice cover extends
the period of hibernal darkness. If the ice is covered by snow under-ice irradiance
can be reduced to
mol
photons m
2
s
1
have been measured even in midsummer (June) below a sea-ice
cover and a snow layer of 30 cm in June on Arctic Spitsbergen (Hanelt et al.
2001
).
So, seaweeds can be exposed for long periods to darkness and very low light
conditions. However, when the sea-ice breaks up solar radiation can penetrate
deeply into the relatively clear water. In October/November 1993, average midday
irradiances as high as 70
2% of the surface value. Extremely low irradiances
6.5
m
<
mol photons m
2
s
1
were measured in 30 m water depth
at King George Island (G´mez et al.
1997
). At Signy Island (South Orkney Islands),
the mean 1% depth of surface photosynthetically active radiation (PAR) is at about
29 m (Brouwer
1996a
). Ultraviolet (UV) radiation as well can go down to consid-
erable depths. In coastal areas, the 10% level for UV-A/UV-B radiation can be
as deep as 7.1/4.3 m water depth, respectively, in summer (Richter et al.
2008
).
m
C. Wiencke (
*
)
Department Seaweed Biology, Section Functional Ecology, Alfred Wegener Institute for Polar
and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
e-mail:
christian.wiencke@awi.de
C.D. Amsler
Department of Biology, University of Alabama at Birmingham, Birmingham, AL 35294-1170,
USA
e-mail:
amsler@uab.edu
