Invasive alien species in Switzerland - Schweizer ...

An inventory of alien species and their threat to biodiversity and economy in Switzerland FOEN 2006 122
emptying into the Atlantic, as its life history involves spawning grounds in the Sargasso
Sea. It has itself been introduced to some parts of Europe, e.g. the Danube basin.
The construction of the Rhine–Danube Canal opened the way from the Rhine, where it
is native, to the Danube basin.
Another nematode was accidentally introduced into Europe together with its North
American host, i.e. Baylisascaris procyonis (Stefanski & Zarnowski) with the raccoon,
Procyon lotor (L.) (see mammal chapter). This species is of concern for human health.
7.2 Flatworms – Turbellaria, Plathelminthes
In the group Turbellaria (part of the Plathelminthes), one species is an abundant alien
inhabitant of lakes and rivers, including the Rhine in Switzerland. The predatory
aquatic flatworm Dugesia tigrina (Gerard) is abundant and widespread in standing and
slow-moving water bodies in Europe (Pöckl and Rabitsch, 2002). It was probably
introduced on aquarium plants or fish from North America around 1900. Although this
species is found in high densities, a negative impact has not (yet) been shown.
Other flatworms of environmental concern are terrestrial. The New Zealand flatworm
(Artioposthia triangulate (Dendy)) (see Fact Sheet) serves as an example of several
predatory flatworm species introduced into Europe from New Zealand and Australia.
Native earthworms are a major prey for these flatworms. Earthworms play an important
role in nutrient cycling in soil, so that their reduction could lead to ecosystem
changes. They are also a significant element of vertebrate prey.
7.3 Segmented worms – Annelida
The Ponto–Caspian invaders in European waters are an interesting group – see the
Crustacea Chapter for more information. The annelid polychaete worm Hypania
invalida (Grube) has become very numerous in the sandy sediment of the Rhine, where
it burrows its tubes vertically into the mud (Rey and Ortlepp, 2002; Van der Velde et
al., 2002). The impact of this abundant species has not been evaluated. It is approximately
1–2 cm long and can reach densities of about 10,000 individuals per square
metre. The species reached the Rhine after the opening of the Rhine–Danube canal,
probably in the ballast tanks of ships.
Another possibly harmless species in the group Annelida, but an oligochaete worm
(Tubificidae), is the large (up to 20 cm long) Branchiura sowerbyi Beddard, which
originates in south-eastern Asia. It was probably introduced on tropical aquatic plants
at the beginning of the 20 th century. At first it occurred only in greenhouses, but it
adapted to the colder climate and is now found in many slow-moving rivers (Pöckl and
Rabitsch, 2002). It lives in self-made tubes in muddy soil and feeds on detritus.