Recent invasions of alien macroinvertebrates and loss of native species in the upper Rhine River, Germany

Dietmar Bernauer

doi:10.3391/ai.2006.1.2.2

Abstract

In the summers of 2003-2005 we sampled the macroinvertebrate community of the upper Rhine River at 28 locations between kilometer 351.9 and 399.5 with a dredge and a hydraulic grab from a ship, or by hand sampling. Additionally, 16 samples were obtained from the cooling water intake screens of a thermal power plant in 2003. A total of 133 species and higher taxa were identified from approximately 140,000 organisms. A total of 33 neozoa (alien) species were identified, including the first record of Chelicorophium robustum in the Rhine River. Neozoa contributed approximately 74% to the total number of organisms collected from the ship-based samples and 85% to those from the power plant cooling water. Almost 64% of all individuals from the cooling water intake belonged to the Ponto-Caspian amphipod Dikerogammarus villosus. Similarly, only 13 taxa, four native and nine alien species, numerically dominated in the ship-based samples, representing 95% and 98% of all organisms in 2003 and 2004, respectively. The nine alien species contributed 74.7% and 72.1%, respectively, to the number of organisms. Only six species occurred abundantly in the main channel of the Rhine River, five of which were neozoa: Jaera istri, Dikerogammarus villosus, Dreissena polymorpha, Chelicorophium curvispinum, and Hypania invalida. The six abundant species colonized nearshore substrates, whereas only few species were retrieved at low densities from the bottom gravel of the central shipping lane. Species diversity was generally higher and relative abundance of neozoa was lower in backwater areas than in the main river channel. Some pronounced changes in the abundance of three numerically dominant species, including the neozoa D. polymorpha and C. curvispinum, occurred between 2003 and 2004, which likely correlated with differences in water levels and temperatures. Overall, our results demonstrate that the macroinvertebrate community of the upper Rhine River has been severely altered by the invasion of several highly successful alien species and the disappearance or population decline of native species, and that these processes are still ongoing. Changes in species composition and relative numerical abundance indicate both a displacement of native species by invasive species, and a relative rapid succession in the numerical dominance of “old“ neozoa and “new“ neozoa.

Highlights

Macroinvertebrate species richness of the Rhine River has been substantially reduced during the last century, mainly because of anthropogenic impacts, such as declining water quality and alterations to river morphometry and hydrology (Kinzelbach 1982, 1983)
27 species of neozoa (Table 2) with approximately 34,700 individual were identified, including all invasive species found in the power plant samples
In 2004, approximately 88,800 organisms from 114 species/taxa were collected, of which approximately 64,000 organisms belonged to 27 alien species (Table 2)

Summary

Introduction

Macroinvertebrate species richness of the Rhine River has been substantially reduced during the last century, mainly because of anthropogenic impacts, such as declining water quality and alterations to river morphometry and hydrology (Kinzelbach 1982, 1983). By the early 1970s, less than one fourth of the more than 160 species identified prior to 1920 could still be found in the river (Titizer et al 1991). The water quality of the Rhine River has substantially improved over the last 30 years, and while macroinvertebrate species richness has largely recovered to former numbers, community composition has been substantially altered primarily by invasive species (IKSR 2002). With the opening of the Main-Danube canal in 1992, one further route for the exchange of biota between the Rhine.

Objectives

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Results