Science Facing Aliens - Invasive Alien Species in Belgium - Belgian ...

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The non-indigenous species list
The discovery of America (1492) is set as the historical baseline for this assessment. This year
marked the beginning of a strong increase in trans-Atlantic shipping. Associated with
shipping, an increase in commerce between continents, their cultures and species evolved.
Shipping and commerce are two important vectors for the ‘transport’ of non-endemic species.
Species that arrived after 1492 in our waters are classified as non-endemic or alien. Those for
which information indicates that resident populations existed before this reference year are
considered as endemic.
The list strives to include all currently known non-indigenous and cryptogenic species
registered in salty and brackish environments in the Belgian part of the North Sea, the Belgian
coastal zone and adjacent estuaries of the rivers Yser and Scheldt (see figure 1). The Ostend
Sluice dock, an artificial water body connected to the port docks of Ostend, is also part of the
study area. The initiative of the VLIZ Alien Species Consortium scrutinizes intentional and
unintentional introductions by man or other vectors. Alien species for which there is no
evidence of resident populations are not included in the list, nor are species that are limited to
the fresh water environment. Vagrant species or occasional observations therefore are not part
of the scope. New arrivals as a consequence of naturally induced migrations are also
excluded. To this purpose the possible effects of global warming are not accounted for in the
list.
Figure 3: map of the study area
The trend in the number of observed non-endemic species in the Belgian part of the
North Sea and adjacent estuaries is on the rise (figure 2). The steep increase from the 1980’s
onwards is largely due to an increased and improved observation effort. Therefore data before
1980 can not be compared to data after 1980.
Currently (May 2009), the list contains 64 resident non-endemic species. Figure 3
shows the distribution of these resident non-endemic species by larger groups. The arthropods
count the highest number of non-endemic species (23). In this group, the share of Cirripedia
(barnacles) is significant (5). Molluscs (i.a. bivalves and gastropods) and algae contribute
with respectively 11 and 10 species.