View - ResearchGate

Effects of Invasive Non-Native Species on the Native Biodiversity in the River Rhine 263
50
40
30
20
10
0
1831-1850
1851-1870
1871-1890
1891-1910
1911-1930
1931-1950
1951-1970
1971-1990
1991-2005
Cumulative number of species
Fig. 15.2 Increasing number of non-native macroinvertebrate species colonising the
river Rhine. Cumulative data are shown for periods of 20 years (note: the last bar
includes data for only 15 years). The exponential model was fitted by least-squares
regression (y=5.5936 x 10 –22 e 0.0265t , n=9, R 2 =0.98, t indicates the year). Data were
obtained from Tittizer et al. (2000), Geitler et al. (2002) and Rey et al. (2004)
duced by fishermen, another seven species (26 %) having been inadvertently
introduced by the aquarium trade. Interestingly, among the phytoplankton,
an ecologically important group, no non-native species have yet been
observed in the Rhine (Nehring 2005).
About one of two non-native aquatic species entering German rivers could
spread over large areas, and about one of five non-native species have become
invasive (Nehring 2003). In the Rhine delta in The Netherlands, the proportion
of non-native species in the biodiversity of river channels and floodplain
lakes ranges from 7–10 % among macrophytes to 5–12 % among macroinvertebrates
and 17–19 % among fish (Van den Brink et al. 1996). In the Middle
and Upper Rhine, non-native species represent 10–15 % of total species richness
(Haas et al. 2002). Non-native species dominate in terms of total abundance
and biomass, however, the values exceeding 80 % (Tittizer et al. 2000;
Haas et al. 2002).
Thus, species composition in the river Rhine has changed remarkably in
the past four decades. Replacing characteristic riverine species, large numbers
of euryoecious and non-native species, in particular macroinvertebrates and
fish, have invaded this river system (e.g.Van den Brink et al. 1988, 1990). Some
of the species entered the river via ports and estuaries, and then moved
upstream whereas others moved downstream after entering via canals. Several
of these species have penetrated into the larger, still-water expanses but