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4 Discussion
The functional trait composition of the benthic assemblages in the German Bight
indicates that the benthos of the south-eastern North Sea is generally dominated by
small-sized and short-living opportunistic species. A dominance of opportunistic
species is often characteristic for disturbed ecosystems (Borja et al.
2003
; Thrush
et al.
1998
). In the North Sea various anthropogenic stressors (e.g. bottom trawling,
eutrophication) have modified the benthic communities towards a suppression of
large, long-living species, which were replaced by small, opportunistic species
(Kaiser and Spencer
1996
). For example, continuous physical disturbance of the
sea
oor by bottom trawling prevents the recovery of benthic species with multi-
annual life spans, low recruitment and slow post-recruitment development (Kroger
2003
). These organisms are out-competed by opportunistic taxa with high
recruitment rates and are, thus, at high risk of regional extinction (Calabretta and
Oviatt
2008
).
The test for homogeneity of multivariate dispersions revealed no differences
among the three sampling sites (i.e. FSd, SSd and WB; p > 0.05). Several envi-
ronmental parameters may have contributed to the observed homogenization of
benthic assemblages. However theoretical and empirical surveys have demonstrated
that increased homogeneity mainly owing to anthropogenic and climatic distur-
bances (Passy and Blanchet
2007
). Widespread anthropogenic and climatic pres-
sures increase the harshness of habitat conditions and thus, reduce compositional
heterogeneity among sites by decreasing the stochastic processes in structuring
assemblages (Donohue et al.
2009
; Olden and Poff
2004
).
Pairwise test identi
fl
cantly different (p < 0.01) from
the other three sites in terms of variability in species composition. It is likely
resulted from a lower species richness as well as from the numerical dominance of a
few species (i.e., Nucula spp. and Owenia fusiformis constituted >50 % total
benthic abundance). Numerical dominance of few species can be indicative of a
highly stressed ecosystem (M
é
ndez
2002
). Slt was located in the innermost German
Bight, in front of the mouths of the rivers Weser and Elbe. In addition to the role of
the general large scale in
ed solely Slt as being signi
uences (e.g. bottom trawling) in the shaping of the entire
German Bight ecosystem, it seems that some local scale drivers (e.g. river water run
off), in particular, have caused drastic changes in the benthic assemblages at the Slt
site. The possible effect of riverine discharge could be a function of the interaction
between physical processes (e.g. sedimentation and advection) biological processes
(e.g. losses via low-salinity intolerance) and chemical processes (e.g. nutrient
enhancement) (Palmer et al.
2000
). The functional trait composition were different
among all four sampling sites (Fig.
2
). For example, the benthic assemblage at the
station WB showed a higher proportion of long-lived species suggesting more
stable conditions and less disturbance in deeper offshore waters. Assembly theory
for ecological communities suggests that two processes, i.e. competition and abiotic
fl
filters that select individual taxa from a regional pool
because they own a certain set of traits suitable for a given habitat (D
filtering (i.e. ecological
í
az et al.
1998
;
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