Seaweeds and Their Communities in Polar Regions - Seaweed Biology - page 265

Deep water species are strongly photoinhibited when exposed to high light
conditions and recover during subsequent exposure to favorable light only slightly
and slowly (Hanelt 1998 ; Karsten et al. 2001 ), whereas in eulittoral and upper
sublittoral species the decrease in photosynthetic activity is less pronounced and
usually a strong and quick recovery is recorded.
Similarly, UV radiation is also regarded as key factor affecting the depth zonation
of seaweeds (Karsten et al. 2011 ). As explained in Chap. 20 by Bischof and Steinhoff,
UV-B radiation has damaging effects on various cellular structures and processes,
among those on the DNA and photosynthesis. However, damage can be repaired and
there are also protective mechanisms to prevent damage. The result can be impaired
growth or impaired reproductive capacity. The life-history stages of seaweeds most
susceptible to UV radiation are spores. Field experiments have clearly shown that the
upper depth distribution limit of Arctic kelps is determined by the UV susceptibility
of their spores (Wiencke et al. 2006 ). Consequently, the succession of polar seaweed
communities also depends on the UV radiation regime as explained below. Certainly,
metabolic carbon balance and UV radiation are not the only factor controlling the
lower and upper depth distribution limits. Substrate, ice abrasion, and competition
play besides other factors important roles.

13.3.3 Temperature Requirements and Geographic Distribution

Polar seaweeds are well adapted to the low seawater temperatures, and Antarctic
seaweeds more strongly than Arctic species due to the longer cold-water history of
the Southern Ocean (see Chap. 18 by Bartsch et al.). Sporophytes of endemic
Antarctic Desmarestiales, for example, grow up to 5 C and exhibit upper survival
temperatures (USTs) of 11-13 C. Their gametophytes grow up to 10 or 15 C with
USTs between 15 and 18 C (Wiencke et al. 1994 ). The Antarctic red algae
Georgiella confluens , Gigartina skottsbergii , and Plocamium cartilagineum grow
at 0 C, but not at 5 C and have USTs as low as 7-11 C (Bischoff-Basmann and
Wiencke 1996 ). Antarctic cold-temperate species, especially from the eulittoral, are
characterized by higher temperature ranges (Wiencke et al. 1994 ;G´mez et al.
2011 ).
In contrast, sporophytes of the endemic Arctic kelp Laminaria solidungula grow
up to temperatures of 15 C with optimum growth rates at 5-10 C and an UST of
16 C. The gametophytes of this species exhibit an UST of 20 C (Bolton and L uning

1983 ; tom Dieck 1992 ). No data are available on the temperature demands of other
endemic Arctic species. The Arctic cold-temperate red alga Devaleraea
ramentacea grows at temperatures up to 10 C and exhibits USTs of 18-20 C
(Novaczek et al. 1990 ; Bischoff and Wiencke 1993 ). Clearly, more data are needed
also on the temperature dependence of other processes in the life history.
The strong adaptation of Antarctic seaweeds to low temperatures is also reflected
in their photosynthetic performance. Maximum photosynthetic rates of endemic
Antarctic species are at 0 C in a similar range compared to temperate species

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