With reference to the article on Zebra mussels (NCE Water Supplement 28 September) I felt compelled to make the following comment in addition to what had been written.
I understand that one of the more serious effects of zebra mussel infestation on steel is that of corrosion, particularly on sheet or single piles.
Although I have no experience of zebra mussels I have seen from my own accelerated low water corrosion surveys that where acorn mussels are well established on a steel pile surface pitting of the steel can occur directly underneath each individual mussel.
This pitting has the appearance of a pock mark, slightly smaller than the base of the mussels and in some cases up to 2mm or 3mm deep. An unprotected surface covered by mussels can develop quite an advanced state of surface breakdown.
Coatings, however, do seem to offer a resistance to the mussels' surface contact juices or at least appear to act as some form of protection barrier to the steel.
This is just another issue in the complicated story of accelerated corrosion of marine steel piles where it is recommended that such structures be examined carefully all over.
Jamie Christie (M), Aberdeen Harbour Board, 16 Regent Quay, Aberdeen, Scotland, AB11 5SS.