Global Seaweed Biogeography Under a Changing Climate: The Prospected Effects of Temperature - Seaweed Biology - page 382

(Figs. 18.1 and 18.2 ). Two examples shall demonstrate resulting consequences.
Along the coast of China and Japan tropical winter temperatures will not change in
the future so that the 22 C February isotherm will stay at approx. 23 N (Fig. 18.1b ).
In contrast, the corresponding 29 C summer isotherm characterizing the warm-
temperate/tropical boundary nowadays will move from approx. 23 N up to the
Yellow Sea and Strait of Korea to approx. 36 N(Fig. 18.2b ). Hence, this whole area
will become a transitional region where biota will experience a reorganization
according to the individual growth, reproduction, and lethal limits of the species
present (van den Hoek 1982a , b ; see Chap. 3 by Eggert). These temperature changes
will probably also have consequences for the intensive seaweed aquaculture industry
along the Chinese and Japanese coastlines (see Chap. 22 by Buchholz et al.). Another
prominent example of a future transitional region is the west coast of S-America. The
current austral 21 Cwinterand26 C summer SST delimit the biogeographical
boundary between the warm-temperate and tropical regions approx. at a latitude of
5 S (northern Peru). According to our simulations, both isotherms will move south-
wards to approx. 10 S in future austral winter or to approx. 20 S (northern Chile) in
future austral summer. The difference between the current and future boundary region
thereby spans either 5 or 15 latitude (Figs. 18.1 and 18.2 ). Thus, a coastline of more
than 1,000 km length will become a biogeographical transition region and composi-
tion of biota will probably change. It should be noted, however, that due to the
influence of the cold Humboldt current and coastal upwelling regions in general,
biogeographical regions may not always correspond to the system developed by
Briggs ( 1995 ) and the model assumptions. Recent evidence, for example, suggests
that the northern boundary of the cold-temperate region along the western coastline of
S-America set to approx. 40 SbyBriggs( 1995 ) actually extends further north to
approx. 30 S(Camus 2001 ; see also Chap. 14 by Huovinen and G ´ mez).
In addition, the model data identify areas where winter and summer isotherms
and thereby possibly the whole biogeographical region will shift homogenously.
Examples are the warm-temperate region in eastern and western S-America or the
tropical region along eastern and western southern Africa (Figs. 18.1b and 18.2b ).
Although it is not yet predictable whether minimal and maximal or mean annual
SST or altogether will be most responsible for shaping future phytogeographical
regions, our data obviously show that new correlations of biogeographical regions
with SSTs will establish.
18.3.4 Specific Effects of Oceanic Warming on Seaweed
Distribution and Ecology
18.3.4.1 Polar Regions
Since the late 1970s the glacial ice sheets have retreated by up to 2% per decade
(Serreze et al. 2007 ) and the Arctic will probably be ice free by the end of this