Terps, borgs and the pink granite coast: It's not easy being green

While we were in Brittany some of the beaches were covered with a spongy green that we thought initially must be a soft marshy grass growing across the sand. We explored, only to discover it was deposits of argues verte, sea lettuce or seaweed. Or kelp.

When times are right, as now, when the temperatures are mild and the seas slow, shallow and incubator-warm, when there is nitrogen and phosphorus present, conditions are prime for the appearance and rapid growth of sea lettuce. Tons of it.

At places it lies over the sand as thick and mounded as green rocks and is often called the 'green tide'.

When conditions are wrong, when temperatures rise and the seaweed dries out, crusts up, decomposes, and is disturbed, it can be lethal. People and animals have died from the ammonia and hydrogen sulphide that is released when the beds are turned in its toxic state.

Since prehistoric times seaweed has been used as a fuel, then it was hand-harvested along the Brittany coast. Over time gatherers loaded their horse drawn carts with it, as they carried it off as a free fertiliser -- given its high potassium content. Harvesters dried it out, lay it on the sand, then burned it in long shallow stone-ovens along the beaches.

Even Napolean found it incredibly useful. Iodine as an antiseptic had not long been discovered, and when his wars were being waged there was a need for large quantities of antiseptic for injuries. So Napolean found it beneficial to build factories in Brittany to extract iodine from the harvested seaweed. Some 25 tons of seaweed were needed to make just 15kg of iodine.

Machines have taken over and now move masses of it by the ton. Seaweed is now used in all sorts of applications including glass manufacture, face masks in beauty therapy, as a setting agent in food technology such as desserts, jellies and custards, and even as a jell in toothpaste.

Some 80,000 tons of seaweed are collected from the coast of Brittany each year and over 500 people are employed in its collection and associated industries.

It has been called the 'green gold of Brittany', and given how much there is, that is not surprising.