During a period when there was considerable capital dredging in
progress in the Conwy Estuary, the shell boring parasite Polydora ciliata
became unusually frequent resulting in both loss of condition and higher vulnerability to
predation by crabs (Ambariyanto & Seed, 1991). Mass mortalities of farmed mussels have
been attributed to the parasite Mytilicola intestinalis but this was considered by
Bower (1992) to be unsubstantiated (see chapter IV).