Biology Reference
In-Depth Information
These relatively high light conditions prevail until phytoplankton blooms are
formed and turbid melt-water carrying fine sediments and detritus flows into the
sea (Drew and Hastings
1992
). Thus, favorable light conditions for algal growth are
present for only 2-3 months per year.
In contrast to the strong seasonality of the light conditions, seawater
temperatures in the sublittoral vary only slightly between
1.8
C in winter and
2.2
C in summer in the Antarctic Peninsula region (Drew and Hastings
1992
). At
the boundary of the temperate region, maximum temperatures can reach 5
C in the
Antarctic and 8-10
C in the Arctic (Wiencke et al.
2007
). Temperature variation is,
however, stronger in eulittoral and supralittoral communities. On King George
Island, temperatures can go up to 14
C in tide pools while seaweeds exposed to
air in the supralittoral experience temperatures up to nearly 30
C in summer and
down to
27
C in winter (Zacher et al.
2011
).
Although the current water temperatures in both polar regions are similar, the
Arctic Oceans differ considerably in their cold-water history and their genesis.
Whereas the water temperatures in the Southern Ocean have been low for
14 million years, glaciation and a winter sea-ice cover did not develop earlier than
two million years in the Arctic (Crame
1993
; Zachos et al.
2001
; Zacher et al.
2011
). Other differences between both polar regions refer to the connection with the
temperate regions and to the nutrient levels in the seawater. Whereas the Antarctic
region is strongly isolated, the Arctic region is continuously connected to temperate
coasts. With respect to the nutrients, levels of nitrate and phosphate are high
throughout the year in the Southern Ocean (Drew and Hastings
1992
; Ducklow
et al.
2007
), while there is a strong seasonal variation of these levels in the Arctic.
Here, nutrient levels are usually high during winter only and drop suddenly after
sea-ice breakup (Chapman and Lindley
1980
; Aguilera et al.
2002
).
Seaweeds growing in such an extreme environment have to be adapted to these
conditions. Their seasonal development must be tuned to the strong seasonality of
the light conditions. Species from the Arctic must furthermore be adapted to the
seasonal changes of the nutrient concentrations. An important prerequisite for
seaweeds from polar waters is their capability to utilize the—for most parts of the
year—prevailing low light conditions and, on the other hand, to sustain and use as
efficient as possible the high light conditions during spring for photosynthesis.
The difference in the cold-water history of both polar regions has forced
seaweeds in the Antarctic to reduce their temperature demands considerably com-
pared to species from the Arctic (G´mez et al.
2011
). Moreover, in conjunction with
the strong geographic isolation of the Antarctic region, this has had great effects on
biodiversity: Whereas in the Arctic only few endemic species occur, endemism is
high in the Southern Ocean (Wulff et al.
2011
). These environmental forcings
influenced also the biotic interactions between seaweeds and their associated
organisms. As we will discuss below, all these factors are important determinants
of the functioning of polar seaweed communities.
