Thursday, September 16, 2010

Postcard from Essaouira: Teredo 'worm' threatens boats

The livelihood of the fishermen in Essaouira is being threatened by a mollusc that is eating away at their boats.
The teredo or 'shipworm' is a type of saltwater bivalve mollusc known to bore into and eventually destroy wooden structures immersed in sea water. More and more of the blue fishing boats in Essaouira are being put into dry dock, taken apart, repaired and being put back together. The problem has increased over the last four months. There have always been attacks of the teredo, but it's getting worse - probably because of global warming producing warmer waters.

the teredo mollusc

When shipworms bore into submerged wood, bacteria in a special organ called the gland of Deshayes allow them to digest cellulose. The excavated burrow is usually lined with a calcareous tube. Shipworms have slender worm-like forms, but nonetheless possess the characteristic structures of bivalves. The valves of the shell of shipworms are small separate parts located at the anterior end of the worm, used for excavating the burrow.

damage caused by the teredo

They're pretty hardy, too. Mooring boats in fresh water or putting them in dry dock for weeks at a time doesn't always get rid of the borers. Since ancient times, fishermen have been daubing the hulls of their boats with tar or special paint to prevent an attack. However, this is an expensive process and the fishermen in Essaouira simply can't afford it.

The artisanal fishing fleet is very important in Morocco. There are over 20 000 wooden boats along the coast and most of them are built in Essaouira. They are usually 5,40m long with a width of 2m and a draught of 0,45m. They can face the heavy seas of the Atlantic and have exceptional sailing qualities.

Boats made of modern materials such as glass fibre and polyester resin to the same design are also manufactured in Morocco, for export mostly to France. As they're much lighter than the original wooden boats, 100kg of ballast has to be added to the keel to give them the same stability and unsinkability. These boats, of course, would not be subject to attacks by the teredo. But again, Essaouira's fisherman can't afford modern versions of their ancient craft.

Essaouira photos: Kirsty McArdle

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