The edible periwinkle, littorina littorea, is a herbivore, feeding on diatoms, algal sporelings, vegetable detritus and larger weeds.
Growth rates vary over time, with least growth occurring in winter as air and sea temperatures fall. It is fairly rapid up to 12 mm, becoming reduced as the animals get older and larger.
The edible periwinkle reaches a commercially viable size at 16 mm. It is estimated that up to 30 per cent of the winkle crop is discarded by the wholesalers as being undersized. Approximately £5 million of periwinkles are exported from Ireland each year.
There is a large market for the edible periwinkle on the continent, principally in France and Spain. The European market prices vary from £600-£1,000 a tonne in the summer to £1,700 a tonne at Christmas.