Naval shipworm facts for kids
Quick facts for kids Naval shipworm |
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Teredo navalis, often called the naval shipworm or turu, is a type of saltwater clam. It's a marine bivalve mollusc that looks a lot like a worm. Even though it's called a "shipworm," it's actually a clam! It has a small shell at one end that helps it bore into wood.
This shipworm might have first lived in the northeast Atlantic Ocean. But it has now spread all over the world. It digs tunnels into wooden piers, docks, and the bottoms of wooden boats. This makes it a big problem because it can cause a lot of damage to underwater wooden structures.
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What Does a Shipworm Look Like?
The Teredo navalis has a long, reddish body that looks like a worm. This body is completely hidden inside a tunnel it makes in wood that is floating or underwater. At the front of the animal, there are two small, triangle-shaped plates. These plates are made of calcium carbonate, which is like the material in chalk or seashells.
These plates are about 2 cm (3⁄4 in) long. They are the shipworm's shell, similar to the two halves of a regular clam shell. They are white with a thin, pale brown covering. The plates have rough ridges that help the shipworm grip the wood. It uses these plates to slowly make its burrow bigger.
The shipworm also has two tubes, called siphons, that can stretch out or pull back. These siphons stick out through a small hole at the entrance of its tunnel. One siphon brings in water, and the other pushes water out. If the shipworm feels danger, it can pull its siphons inside the tunnel. A pair of hard, oar-shaped plates then block the tunnel opening to protect them.
The tunnel itself is round and lined with a chalky material that the shipworm creates. It can be up to 60 cm (24 in) long and 1 cm (1⁄2 in) wide.
Did you know? Shipworms are edible! People on the island of Marajó and in parts of Thailand traditionally eat them. They are often said to taste like clams or oysters and are cooked in similar ways.
Where Shipworms Live and Spread
Teredo navalis can be found in warm and mild seas and oceans all over the world. It's hard to know exactly where they first came from. This is because they have spread so well by traveling on floating wood and the hulls of ships.
You can find them near the shore, living inside underwater wood. This includes docks, old wooden posts, driftwood, and the wooden parts of boats. They can live in slightly salty water (brackish water) as well as the open sea. They can handle different salt levels, from five to thirty-five parts per thousand.
Shipworms also do well in many different temperatures. They can survive in water as hot as 30 °C (86 °F) and as cold as 1 °C (34 °F). However, they grow and reproduce best when the temperature is between 11 to 25 °C (52 to 77 °F). They can even live without air for about six weeks by using up stored energy.
New shipworm groups start when tiny larvae (baby shipworms) float with ocean currents. They also spread when pieces of wood they live in drift to new places. Historically, they traveled on the wooden hulls of ships to new parts of the world. In the Baltic Sea, there were many shipworm outbreaks in the 1930s and 1950s.
Life Cycle and Reproduction
Shipworms get their food from the water that passes through their gills. They mostly eat tiny pieces of wood they scrape off. But they also eat some tiny algae from the water. Their gills also have special bacteria that help them digest the wood. These bacteria produce enzymes that break down the cellulose in the wood.
Waste, reproductive cells (like sperm and eggs), and tiny larvae are released from the back of the burrow. This part of the tunnel is open to the sea through a small hole.
Teredo navalis is a hermaphrodite, which means it can be both male and female. All shipworms start their adult life as males. They become mature when they are a few centimeters long and release sperm into the sea. In warmer places, they change into females about eight to ten weeks after they settle. But in colder areas, this change can take up to six months.
Eggs are fertilized when sperm gets sucked into a female's burrow through her inhalant siphon. A female can carry more than a million larvae at a time inside her gill chamber. After they grow a bit, these tiny larvae are released into the sea. At this stage, they are called veliger larvae. They have a special part called a velum, which has tiny hairs (cilia) that help them swim and eat. They also have the beginnings of a shell.
These larvae eat tiny ocean plants called phytoplankton and float with the currents for two to three weeks. As they grow, they develop siphons and gills.
When they are ready to change into their adult form, they look for suitable wood to settle on. They seem to be able to find rotting wood and can swim towards it when they are close. Each larva then crawls around until it finds a good spot. It attaches itself with a strong, silky thread called a byssus. It might even make a special chemical to soften the wood before it starts digging with its foot.
Once it makes a small hollow, it quickly changes shape. It sheds and eats its velum and becomes a young shipworm with small, hard shells at its front end. Now it can dig much better. It bores deeper into the wood and spends the rest of its life tunneling inside.
Why Shipworms Are a Problem
Teredo navalis is a very damaging pest for wood that is underwater. In the Baltic Sea, pine trees can be full of tunnels within 16 weeks of being in the water. Oak trees can be destroyed in 32 weeks. Whole trees that are 30 cm (12 in) wide can be completely ruined in just one year.
Shipworms attack the wood of ships, destroy shipwrecks, and damage sea defenses like dikes. Around 1730 in the Netherlands, shipworms were found to be seriously weakening the wooden walls that protected the land from the sea. To stop floods, these wooden walls had to be replaced with heavy stones, which cost a lot of money.
When the shipworm arrived in San Francisco Bay around 1920, it caused huge damage to the piers and docks in the harbors. It has spread in the Pacific Ocean. Its ability to live in less salty water has caused damage in areas that were not affected by local shipworms before.
In the 1700s, the Royal Navy (Britain's navy) started covering the bottoms of its ships with copper. This was an attempt to stop the damage caused by shipworms.
So far, no treatment for wood has completely stopped shipworm attacks. In the 1800s, the Dutch tried many things like linseed oil, metal paint, powdered glass, and burning the outer layers of the wood. None of these worked well. They also tried covering wooden posts with carefully placed iron nails, but this didn't last either.
In 1878, people found that creosote could help. Creosote is a type of oil. It worked best on soft, resinous woods like pine. For harder woods like oak, the creosote had to soak all the way through the wood to be effective.
Underwater shipwrecks have been protected by wrapping them in special fabrics called geotextiles. These fabrics create a physical barrier to stop the larvae. Another way to protect wrecks is to rebury them in the mud at the bottom of the sea. But even with these efforts, a permanent solution to stop shipworm damage has not yet been found.
See also
In Spanish: Teredo navalis para niños
