PROLIFIC OR WHAT?

For such small creatures, mussels produce astonishing numbers of eggs: 5 million for a 7 cm mussel, up to 40 million for a large mussel. Per year! Male mussels work even harder - they produce 10,000 spermatazoa per egg. The eggs are released as plankton, measuring a few hundredths of a millimetre and inevitably 95 per cent or more rapidly die or are consumed by other sea creatures including adult mussels. After a few weeks survivors settle on seaweed, the sea floor or on capture devices such as ropes. Now they grow to a couple of millimetres, beginning to develop their beard or byssus which attaches the mussel to its landing point (and is astonishingly strong and well-engineered - the picture is by courtesy of MIT). The mussel will now grow by up to a centimetre a month in good conditions.

The tiny settled baby mussels are known as spat and mussel farms collect wild spat each year to provide new crops of mussels. In New Zealand thousands of tons of seaweed covered with tiny mussels are collected from beaches to keep mussel farms in business.

In Europe the spat is often collected by suspending “hairy” ropes above wild mussel beds. The availability of spat varies tremendously and in poor years mussel farms suffer decreases in production for lack of spat. Given that demand for spat has risen rapidly over the last 20 years, there have been several attempts to establish experimental hatcheries.

Most mussel farms use ropes suspended from buoys or rafts to raise their spat to commercial size, which takes 12-24 months. A raft might carry as much as 30 tonnes of mussels with a rope supporting 20kg of mussels per metre. A minority of farms–especially Dutch–grow their mussels on the sea bed.