Re: Why are zebra mussels not a problem in Western Europe ?

Your question stumped me - so I have consulted with another expert, who 
posted the answer you see below.

"Zebra mussels are a problem in Europe as well; however, they have lived
with them so long that you don't hear anything special about it.

Further considerations:
1.  In the UK, mussel densities in most places are much lower than the
very high densities found in many other places.  Possibly because of
chemical differences in the water, so they are generally not as much of a
problem in the UK.
2.  Zebra mussels spread in Europe before and during the beginnings of the
industrial revolution and before the building of electric power plants.
Therefore, when these structures were built, their designs already took
into account the presence of biofouling animals (e.g. designs with dual
water inlets so that one could be shut down for cleaning; designs for
chemical treatments, heat treatments, etc.).  Zebra mussels were
particularly a problem in the US because we never had such a bad
biofouling organism in freshwater environments before, so physical plants
had to be retrofitted at great cost.  This process is still going on.
3.  Ecologically, zebra mussels long ago had their impacts in Europe.
Perhaps this explains why there are are less than 10 unionid mussel
species in Europe, while the US has (had?) over 80 unionid species, many
of which may be headed for extinction because of the zebra mussel."

Dr. Jeffrey L. Ram           
Department of Physiology     
Wayne State University
Detroit, Michigan, USA