Teredo – worms shall devour them

Places matter to people.  In my suburb, one of our best-loved places is the Shorncliffe pier.  Throughout the day, it is a place for tai chi and joggers, crab pots and fishing.  In the early evening, it is full of friendly walkers, with or without dogs.  People sprinkle the ashes of those they love from its railings, or use it as a backdrop for wedding photos.  It was recently used in a UK television ad available on YouTube here.

They used to say that Sandgate is 12 miles from Brisbane – or 13 at low tide.  It is a long way out to deep water, so early settlers could not get their goods – or themselves – from ship to shore without wading.  As the community grew, in 1865 they made plans ‘for the construction of a PIER or LANDING STAGE at Sandgate’.  This pier opened to the public in 1882.

From the start, the pier had a dual purpose, as a commercial landing stage, but also as a popular promenade.  Piers were a part of the tradition of beach ‘watering places’, growing popular amongst all classes by the mid-19^th century.  They were destinations for city day-trippers who came by railway to enjoy a day at the beach, perhaps swimming, but probably just strolling along the waterfront, and enjoying the concerts, food outlets, Punch and Judy shows and other commercial activities that took place on and around a pier.

Our pier followed the social model of British piers such as the West Pier at Brighton (1866) and the Cleveden Pier on the Severn (1869), both built at much the same time.  People came by coach, and then by rail (1882) to enjoy a day at the beach.  But while the British piers were mainly built of iron, wood was much cheaper in Brisbane, so our pier is wooden.

A few weeks ago, council inspectors found marine borers in its timber pilings and the pier has been closed until further notice.  Since then there have been petitions and a rally, a local newspaper campaign and a lot of promises.  A local election next Saturday has raised the temperature.

Generally though, we are all in furious agreement that we love our pier, and want it saved, even though it has no commercial purpose any more, and no one seems to know quite how it can be restored.

The usual culprit in this sort of damage is Teredo navalis, commonly called the shipworm, though it is not a worm, but a bivalve mollusk.  It lives very widely in salt-water environments, wherever there is wood to feed on.  Once it must have depended on the occasional log falling into the sea, but ever since people first went to sea, Teredo has been a problem.

In 1579, Sir Francis Drake spent 5 weeks on the Californian coast repairing the Golden Hind, which had been damaged by shipworms.  He thought they were native to the New World, but they are now so widely distributed that it is hard to tell.  They have certainly moved beyond their original tropical environment, and at present they are invading the Baltic Sea.

Shipworms caused enormous damage to wooden ships.  The best solution, which became standard during the 18^th century, was to clad them in copper sheeting.  It was an expensive solution used for naval vessels and merchantmen, but every ship still needed a skilled ship’s carpenter to deal with the leaks and creaks.  Iron replaced wood by the late 19^th century.

However while iron ships were safe from teredo, the underwater furnishings of a maritime economy – jetties,  wharves, piers, dry docks – continued to be built of wood, particularly in newly settled regions where wood was still plentiful.

A maritime economy based on wood used a lot of timber.  Venice, for instance, consumed all the forests in its hinterland constructing its maritime empire.  A few years ago, I travelled along the Brenta Canal which links Venice and Padua.  The first section of this canal dates back to the 16^th century, and along its edges, there are still sections lined with tree trunks.  Even if they were coppiced tree branches, these banks consumed a great deal of timber cladding.

The British Empire was also a maritime empire.  By the time James Cook first saw the Australian coastline in 1770, the British navy had consumed most of the forests of southern England, and relied on timber from the Baltic and North America.  He thought the tall trees of Australia, such as the pines of Norfolk Island (Araucaria heterophylla) that grow to a height of 65 metres, and other Araucarias, would make ideal masts – though as it turns out, they are rather too brittle.

Other Australian timbers became popular for quite different reasons. Jarrah (Eucalyptus marginata) from Western Australia and satinay (Syncarpia hillii) from Fraser Island, off the Queensland coast, were both considered particularly resistant to attack by teredo, so were used in shipbuilding and for marine pilings.  When the Suez Canal was built in the 1860s, it was lined with satinay logs – some 50,000 of them, according to Fraser Island sources.

Teredo is rapacious, and it seems to strike suddenly.  It ate into the Dutch dyke system several times during the 18^th and 19^th centuries.  In 1917 it appeared in San Francisco, where it caused $15m. worth of damage to the harbour fixings.  Although a salt-water animal, it can survive in brackish water, but the salinity level is important.  One theory is that it may attack after a drought, when salinity rises following a drop in fresh water flows.

Currently it is invading the Baltic Sea which until recently had low salinity levels, but is now becoming more salty.  Maritime archaeologists are worried that it is destroying wrecks on the sea floor.

The shipworm has attacked other piers too.  In an article entitled ‘Pier-eating Monsters’, the Hudson Reporter reported in 2009 that teredos had caused part of a walkway along the Hudson River to collapse.  Ironically, there were no shipworms there for many years because of the level of pollution in the Hudson River.  Now the river is being cleaned up – and teredo is back.

Teredo has no friends, but it does have one claim to fame.  The story goes that the engineer Marc Brunel was first inspired to develop the idea of ‘shield tunneling’ from watching the way the teredo bores into wood from within its enclosing shell.  He and his son, Isambard Kingdom Brunel, built the first tunnel under the Thames using this technique.  It opened in 1843.

Nowadays, according to Wikipedia, Teredo tunnelling refers to something quite different:

In computer networking, Teredo is a transition technology that gives full IPv6 connectivity for IPv6-capable hosts which are on the IPv4 Internet but which have no direct native connection to an IPv6 network.

I haven’t the faintest idea what this means.