Biology Reference
In-Depth Information
seaweed genus diversity peaks in mid latitudes and not the tropical region (Kerswell
2006
; Santelices et al.
2009
; Tittensor et al.
2010
). SST was identified as one
significant predictor of overall coastal species richness (Tittensor et al.
2010
) and
high interannual temperature variability was proposed as explanation for the depau-
perate brown algal flora along the southwest African and north-central Chilean
coastline (Bolton
1996
). Thus, the predicted changes in SST for the end of the
twentieth century will probably have a substantial effect not only on distribution of
seaweeds and marine communities in general, but also on global marine diversity.
Kerswell (
2006
) analyzed the latitudinal pattern of global seaweed genus diversity
and seaweed endemism in detail. As in other coastal taxonomic groups (Tittensor
et al.
2010
) there is a band of high diversity in the northwestern Pacific surrounding
the Japanese archipelago and in the southwestern Pacific along the southern Austra-
lian coastline (Kerswell
2006
). In the Atlantic, there is a major hotspot of diversity
along the European coastline (Kerswell
2006
). All these regions inherit a high
seaweed genus diversity and have been identified by our model data to be impacted
by future warming. Thus, major changes in seaweed species richness, and the
functionality of assemblages through species extinctions, species invasions, and
changes in trophic relationships (Sala and Knowlton
2006
) are expected especially
in these regions. Within the last decade, a wealth of cryptic seaweed species has
been described with the help of modern molecular biological tools (e.g., van der
Strate et al.
2002
; Brodie et al.
2007
; Verbruggen et al.
2009
). Thus, species richness
of marine algae and genetic diversity of their populations probably is strongly
underestimated (Zuccarello et al.
2011
) and thereby possibly also their adaptive
potential to change. But it is not yet clear whether genetic differentiation always
coincides with ecological differentiation (Tronholm et al.
2010
).
18.5 Synopsis
Clearly, the prospected worldwide changes in SSTs will exert a differential pressure
on seaweed species and assemblages along biogeographical regions. As the ice-free
Arctic coastlines and all other regions will expand polewards, the tropical bio-
geographical region will widen considerably. In contrast, there will be almost no
change in the northern limit of the Antarctic region. Most effects on biota will be
expected in biogeographical transition regions which have been identified here, for
example along the warm- to cold-temperate European coastline or along the warm-
temperate to tropical coasts of SW and SE-America, Japan, or China. In these areas,
summer and winter SST will move polewards with a differential magnitude so that
annual temperature gradients will become more pronounced in some areas. Hence,
severe biotic changes are expected as the assemblages characterizing the biogeo-
graphic regions will not be able to shift as a whole. Rather, we predict differential
species-specific shifts depending on the respective temperature-dependent life
cycle characteristics of species which additionally will be shaped by other abiotic
and biotic factors. Comparison of coastal areas comprising present-day highest
