Photographer:Christin Appleqvist Affiliation: University of Gothenburg Source: www.eurekalert.org Copyright: CC BY 3.0
Teredo navalis is actually a species of saltwater clam but it is called a shipworm due to its worm-like appearance. It has a long, reddish body that is topped with a very small shell adapted to bore into wood. Teredo navalis ranges from 8-12 in. long to 0.4-0.8 in. wide but in tropical waters they’ve been observed at lengths up to 20 inches. The shell is rigid and only covers about 0.8 inches overall.
The historic negative economic impacts of Teredo navalis invasion may rival those of any other introduced marine species. It is the species believed responsible for a massive infestation of Dutch dikes in the 17th century. The damage inflicted by the shipworms prompted replacement of wooden dikes with stone. Massive T. navalis infestation was also responsible for the destruction of an unknown number of wharves, piers, ferry slips and other wooden harbor structures at a rate of a major structure a week for a period of two years in San Francisco Bay from 1919-1921; in current dollars this would have equated to between $2 billion and $20 billion in damage. In general T. navalis has a centuries-long history of causing damage to sailing vessels, piers, pilings, marinas, and any other submerged wooden structures. In 1946, shipworms were estimated to cause $55 million/year of damage to waterfront structures in the United States. Due to its tolerance of low salinity this shipworm has been able to spread to all coasts of the United States and causing damage every year.
Genus Teredo is unique even among wood-boring bivalves in its ability to feed solely on wood; with the aid of symbiotic cellulolytic, nitrogen-fixing bacteria contained in specialized cells on the gills. Teredo navalis uses its sculpted shell to rasp wood particles and water is obtained through siphons which are used for feeding as well as respiration and excretion/egestion. It takes about five weeks to develop from eggs to metamorphosing larvae. They spend half of this time in the mother’s gill chamber until they are released into the water as free-swimming larvae. As the larvae develop, they transition from being small and white to large and dark grey. Fertilized eggs develop into cilia-covered larvae, referred to as a trochophore. Over time, cilia are seen covering only the velum in larvae, now called veligers. A shell appears about the same time in development as the velum and becomes bivalved after formation. Older veligers are released into the water. During this free-swimming stage, the siphons, gills, and foot develop. Once shipworms attach onto a wooden substrate, metamorphosis is observed.
This shipworm occurred at low densities around Chesapeake Bay as early as 1878. In 1920 it wreaked havoc on the San Francisco Bay for 2 years. Subsequently, Teredo navalis has been collected from North Carolina and southward to Florida, Texas, the Bahamas, and Puerto Rico.
Atlantic coast of Europe from Iberia to Scandinavia
U.S. Habitat: Various submerged wooden substrates including floating wood, ships, or wharfs.
U.S. Present: All coasts of the United States
The naval shipworm is less of a problem today than in the past as a result of many fewer wooden-hulled ships and the widespread use of chemically treated timbers in waterfront construction. However, in the absence of these defenses, it will destroy wooden structures below water.
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