There are few ways to effectively prevent destruction of wood by Teredo navalis. Other non-wooden materials have been used to build objects like ships or wharfs. Biocides are only temporary answers and are hazardous to humans. Use of geotextiles to protect antique ships serves as a physical barrier to naval shipworms.
There is limited information on how T. navalis communicates.
The conservation status of T. navalis has not been evaluated.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Teredo navalis 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 gray. Fertilized eggs develop into cilia-covered larvae, referred to as trochophores. Over time, cilia are seen covering only the velum in larvae, now called veligers. The velum serves as an organ participating in movement and feeding. 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.
Sexes alternate in T. navalis. Young are hermaphrodites while adults are either male or female. Usually, organisms are male first and then become female later. A second male to female phase may occur but shipworms normally do not live long enough for completion of the second phase.
Development - Life Cycle: metamorphosis
Naval shipworms have many negative effects due to their wood boring activity. They have been noted to cause damage in ships and dikes. Weakening of dike gates, combined with a heavy storm, resulted in flooding of the Netherlands in 1731. Teredo navalis also eat away at piers and wharfs. In San Francisco Bay, they can cause 200 million dollars worth of damage yearly.
There are not any mentioned effects of T. navalis that are positive to humans. They do serve as food for Australian natives.
Positive Impacts: food
Naval shipworms break down submerged wooden substrates. The holes they create in the wood can be used by crustaceans such as Idotea. Teredo navalis share a symbiotic relationship with the nitrogen-fixing bacteria within them that help the shipworms digest wood. Some protozoa are known to parasitize this species.
Ecosystem Impact: creates habitat; biodegradation
Naval shipworms primarily feed on wood. They are able to do so because of enzymes produced by the nitrogen-fixing bacteria within them. Teredo navalis use their shell to cut into the wood. The pieces are then transported into the mouth via cilia. Organisms from the water may also be taken up for food via the inhalant siphon. Free-swimming veligers feed on plankton.
Plant Foods: wood, bark, or stems; phytoplankton
Other Foods: microbes
Foraging Behavior: filter-feeding
Primary Diet: herbivore (Lignivore); planktivore
The origins of Teredo navalis are unknown. Appropriately referred to as naval shipworms, T. navalis are molluscs that frequently dwell in the wood of ships. Due to the prominent use of ships in global trade and the consequent dispersal of the shipworms, the origins of T. navalis are uncertain. Masses of naval shipworms were first identified near the Netherlands in the North Sea. They are common to the Baltic Sea as well as the Atlantic and Pacific Oceans today.
Biogeographic Regions: nearctic (Introduced ); palearctic (Introduced ); oriental (Introduced ); ethiopian (Introduced ); neotropical (Introduced ); australian (Introduced ); atlantic ocean (Introduced ); pacific ocean (Introduced )
Naval shipworms are marine and estuarine organisms inhabiting various submerged wooden substrates including floating wood, ships, or wharfs. Part of their larval stage is spent free-swimming in water. While they can tolerate low saline levels (up to 5 ppt), they flourish at levels greater than 9 ppt. Their optimal temperature range is 15 to 25 degrees Celsius and, as a result, T. navalis can be found in temperate and tropical zones.
Habitat Regions: temperate ; tropical ; saltwater or marine
Aquatic Biomes: pelagic ; benthic ; coastal ; brackish water
Other Habitat Features: estuarine
The lifespan of shipworms is 1 to 3 years.
Average lifespan
Status: wild: 1-3 years.
While T. navalis looks like a brown worm on the outside, it is actually a bivalve. Its head is covered with two white, tri-lobed shells used to bore into wood. The shells are up to 2 cm long and have concentric ridges. Inside the shell is a hook-like process called a styloid apophysis. The foot is also at the anterior end. At the posterior end are two siphons: incurrent and excurrent. The former is used for respiration and feeding while the latter is where waste and sperm or larvae exit. Paddle-like pallets act as a lid to cover the siphons when not in use. Naval shipworms are about 20 cm in length but can range from 1.5 to 58 cm. They are 1 cm in diameter. Calcareous coverings are secreted from their mantles that coat the burrows they make. Male and female adults cannot be distinguished externally.
Range length: 1.5 to 58 cm.
Average length: 20 cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike
The calcerous covering they secrete not only act as a lubricant but also deters predators or poisons in the water. In response to these conditions, thicker calcareous material is secreted at the anterior end in addition to the sides. Predators include bacteria and parasitic protozoa like Architophrya. Native Australians and snails also eat naval shipworms.
Known Predators:
While no direct information was found on the mating system of T. navalis, it can be inferred to be polygynandrous. Males release sperm into the water, which females pick up via the incurrent siphon. This occurs on multiple occasions, as females spawn 3 to 4 times per season.
Mating System: polygynandrous (promiscuous)
Reproduction typically occurs in the summer months when temperatures reach 15 degrees Celsius. Females spawn 3 to 4 times per season, each time releasing 1 to 5 million larvae. Teredo navalis embryos spend the first 2 to 3 weeks in the mother’s gill chamber. They are then released into the water as free-swimming veligers. Released larvae are 88 by 75 microns with a depth of 55 to 57 microns. They reach sexual maturity 6 to 8 weeks after inhabiting wood.
As mentioned previously, shipworms alternate between sexes during their life. When larvae mature, half of their gonads become spermatocytes, the other half ovocytes. Usually, spermatocytes multiply faster and are released earlier.
Breeding interval: Shipworms spawn 3 to 4 times each season
Breeding season: Breeding season is usually in the summer
Range number of offspring: 1,000,000 to 5,000,000.
Range gestation period: 2 to 3 weeks.
Range time to independence: 2 to 3 weeks.
Range age at sexual or reproductive maturity (female): 6 to 8 weeks.
Range age at sexual or reproductive maturity (male): 6 to 8 weeks.
Key Reproductive Features: seasonal breeding ; simultaneous hermaphrodite; sequential hermaphrodite (Protandrous ); sexual ; fertilization (Internal ); broadcast (group) spawning; viviparous
Females carry offspring in gill chambers during early development. When larvae reach the advanced veliger stage, they are released into the water. There is no evidence that mothers assist veligers in finding wooden substrates to inhabit.
Parental Investment: female parental care ; pre-hatching/birth (Protecting: Female); pre-weaning/fledging (Protecting: Female)
Teredo navalis, commonly called the naval shipworm or turu,[2] is a species of saltwater clam, a marine bivalve mollusc in the family Teredinidae. This species is the type species of the genus Teredo. Like other species in this family, this bivalve is called a shipworm because it resembles a worm in general appearance while at the anterior end it has a small shell with two valves, and it is adept at boring through wood.
This species may have originated in the northeast Atlantic Ocean, but has spread around the world. It tunnels into underwater piers and pilings and is a major cause of damage and destruction to submarine timber structures and the hulls of wooden boats.
Teredo navalis has an elongated, reddish, wormlike body which is completely enclosed in a tunnel it has made in floating or submerged timber. At the front end of the animal are two triangular, calcareous plates. These are up to 2 cm (3⁄4 in) long and correspond to the valves of other bivalve molluscs. They are white, with a covering of pale brown periostracum, and have rough ridges. The mollusc uses them to grasp the wood and slowly enlarges the burrow in which it lives. It has retractable inhalant and exhalant siphons which project through a small hole in the horny septum which blocks the opening of the burrow. When the animal is threatened, the siphons can be drawn inside the burrow and protected by a pair of calcareous oar-like pallets. The tunnel is circular in cross section and is lined with calcareous material extruded by the mollusc. It can be up to 60 cm (24 in) long and 1 cm (1⁄2 in) in diameter.[3][4] They are edible, and are traditionally consumed on the island of Marajó[2] and parts of Thailand. They're commonly described as tasting like clam or oyster, and are often prepared in similar ways.[5]
Teredo navalis is found in temperate and tropical seas and oceans worldwide.[1] It may have originated in the northeast Atlantic Ocean, but it is difficult to establish where it originally came from because it has spread so efficiently around the world on debris and hulls of ships. It is found in the littoral zone, living inside submerged timber, pilings, driftwood, and in the hulls of wooden boats.[3] It is found in brackish waters as well as the open sea, and tolerates salinities ranging from five to thirty-five parts per thousand.[4] It is also tolerant of a wide range of temperatures. Individuals have survived temperatures as high as 30 °C (86 °F) and as low as 1 °C (34 °F), though growth and reproduction are restricted to the range from 11 to 25 °C (52 to 77 °F).[4] It can also live without air for about six weeks, using up its stored glycogen reserves.[4] Dispersal to new habitats occurs both during the free-living larval stage, by floating timbers carried along by currents, and, historically, from the hulls of wooden vessels. In the Baltic Sea, there were several mass occurrences in the 1930s and 1950s.[6]
Food particles, mostly timber raspings but also some microalgae, are extracted from the water passing through the gills where gas exchange also takes place. The gills also contain symbiotic nitrogen-fixing bacteria, which produce enzymes that help to digest the cellulose in the wood.[3] Waste, reproductive gametes, and larvae are discharged through the back of the burrow, which is open to the sea through a narrow aperture.[7]
Teredo navalis is a protandrous hermaphrodite. All individuals start their adult life as males, becoming mature when they are a few centimetres long, releasing sperm into the sea. In warmer areas they change into females about eight to ten weeks after settling, but this change may take six months before it occurs in colder climates. The eggs are fertilised when sperm gets sucked into the burrow of a female through the inhalant siphon. More than a million larvae at a time are brooded in the gill chamber, after which they are released into the sea as veliger larvae. By this time they have developed a velum, a ciliated locomotory and feeding organ, and the rudiments of a straight-hinged shell. They eat phytoplankton and disperse with the current for two to three weeks. During further larval stages they develop siphons and gills.
When they are ready to undergo metamorphosis, they search for suitable timber on which to settle. They seem to be able to detect rotting wood and are able to swim towards it when they are close enough. Each one then crawls around until it finds a suitable location, where it attaches itself with a byssus thread. It may secrete an enzyme to soften the wood before starting to dig with its foot. When it has formed a hollow, it undergoes a rapid metamorphosis, shedding and consuming the velum and becoming a juvenile shipworm with small horny valves at the anterior end. It can then begin to dig more efficiently. It bores deeper into the wood and spends the rest of its life as a tunneller.[8]
Teredo navalis is a very destructive pest of submerged timber. In the Baltic Sea, pine trees can become riddled with tunnels within 16 weeks of being in the water and oaks within 32 weeks, with whole trees 30 cm (12 in) in diameter being completely destroyed within a year. Ships' timbers are attacked, wrecks destroyed and sea defences damaged. Around 1730 in the Netherlands, shipworms were found to be seriously weakening the wooden dike revetments, and to prevent erosion of the dikes and subsequent flooding disasters the revetments had to be replaced with heavy stones, at great expense.[9] The shipworm's arrival in San Francisco Bay around 1920 heralded great destruction to the piers and wharves of harbours. It has spread in the Pacific Ocean where its greater tolerance of low salinity levels has caused damage in areas previously unaffected by native shipworms.[6]
In the eighteenth century the Royal Navy resorted to coppering the bottoms of its ships in an attempt to prevent the damage caused by shipworm.[10]
No treatment of timber to prevent attack by Teredo navalis has been completely successful. Experiments by the Dutch in the 19th century proved the inefficacy of linseed oil, metallic paint, powdered glass, carbonization (burning the outer layers of the wood), and any of the usual biocides such as chromated copper arsenate. They also attempted covering wooden pylons with precisely arranged iron nails, but this too had no lasting effect. In 1878 it was discovered that creosote was an effective deterrent, though to work best it had to be applied to soft, resinous woods like pine; in order to work on harder woods such as oak, special care had to be taken to ensure the wood was completely permeated by the creosote.[11] Submerged wrecks have been protected by wrapping them in geotextiles to provide a physical barrier to the larvae or by reburying them in the sediment. No permanent solution has been found.[6]
Teredo navalis, commonly called the naval shipworm or turu, is a species of saltwater clam, a marine bivalve mollusc in the family Teredinidae. This species is the type species of the genus Teredo. Like other species in this family, this bivalve is called a shipworm because it resembles a worm in general appearance while at the anterior end it has a small shell with two valves, and it is adept at boring through wood.
This species may have originated in the northeast Atlantic Ocean, but has spread around the world. It tunnels into underwater piers and pilings and is a major cause of damage and destruction to submarine timber structures and the hulls of wooden boats.
