Shipworms, also called by mariners as the ‘termites of the sea’ belong to the genus called Teredo, the most notorious of which is Teredo navalis, originally native to the Caribbean Sea. It is actually a clam that tunnels through wood submerged in the sea. Though the Teredo serves an ecological value in degrading timber that falls to the ocean, it has also caused considerable damage to wooden boats even since man first ventured out to sea. Shipworms have been a bane to ancient mariners till the advent of copper clad ships by the 18th century and modern toxic coatings.
The behavior of the shipworm inspired Marc Brunel, a French engineer, to devise a method, which he patented in 1818, to tunnel under the Thames River in England, the first of its kind ever built under a river bed. His technique called the “tunneling shield” made use of his observations while working on a shipyard on how the valves with fine ridges were used by the Teredo to drill through the wood, while protecting itself from being crushed. The Teredo also secretes a calcium-rich framework that coated the inside surface of the tube, keeping it stable and crush proof.
In modern times, we have yet to escape the wrath of the Teredo. Wharves, piers, jetties and piling started collapsing in San Francisco Bay between 1919 and 1921, resulting in almost 20 billion dollars worth of damage in today’s money, all because of Teredo. The mouth of the Hudson River of New Jersey and New York was once considered a ‘dead’ waterway, devoid of fish life because of the overwhelming industrial pollution since the 1930’s. Ship captains used to sail their boats through NY harbor just to kill off shipworms and barnacles. That’s how polluted it was. In 1972, the US Federal Clean Water Act limited discharge into the rivers and proactively revitalized the waterways. By the 1990’s fish had returned. And so did the Teredo, with a vengeance. During this period also saw the voluntary ban by the lumber industry on the use of creosote and CCA (chromated copper arsenate) to prevent further leaching of the toxic chromium and arsenic to the environment. These wood preservatives prevented fungi from rotting the wood away and also quite good at killing off the shipworms as well. The environmentally sound actions had unintended consequences—piers and piling that no longer used preservatives started collapsing, hollowed through by Teredo worms.
Biology of Teredo
Considering the economic importance of preventing Teredo infestation, it is surprising how little known about the life cycle of this clam. This website is a work in progress and we welcome suggestions and additions to update the information. Some of the biological information comes from our ongoing observations at our marine test site in Panay Island, where mangrove forests serve as home of Teredo bartschi Clapp, 1923.
In general, the sex in the wild is 1 Teredo male per 1,500 females. After fertilizing the eggs by the male Teredo, the developing embryos are protected inside the mother until they develop into larvae competent to colonize other locations outside the home tunnel. Then,the little Teredos settle in the same wood or nearby timber. Then it starts burrowing through the wood as it grows, parallel to the grain, only turning to avoid any knot on the wood or if there is any obstruction. By the time it reaches adulthood, it is already at least a foot long and half inch thick. If you think this is big for a worm, its Sumatran cousin, the Giant Teredo, grows to six feet long, but lives in the muddy bottom of the sea rather than inside wood. Unlike other typical clams, the shell covers only a tiny portion of the Teredo and used more like a drill bit to burrow a circular hole through the wood. The tube-like home is capped at the opening of the burrow with a secreted calcareous cover, with protruding siphons that allow the animal to breathe, feed on plankton and excrete wastes. It appears that the Teredo lives out its life within its tunnel home, continuing to extend the length of its burrow. Actual life span of the Teredo in the wild is not known.
The cellulose that makes up the wood is not sufficiently nutritious as food and the shipworm cannot normally digest it. It overcomes this limitation through a symbiotic relationship with bacteria, Teredinibacter turnerae, in its gills that secrete enzymes, called cellulases and nitrogenases, breaking down the cellulose and fixing nitrogen to build amino acids. Cellulases are the same enzymes, derived from fungi, used to create your stonewashed denim jeans by breaking down the cellulose on the outer surface of the cloth. Now, it is also a major ingredient in most laundry detergents to improve cleaning efficiency. The potential of Teredo-derived cellulases is in its future use in biofuels because it is likely more efficient than fungal cellulases in converting paper-mill cellulose waste into ethanol or methanol
Poseidon Teredo Test Station
The Poseidon Teredo Test Station is located within the mangrove forest heavily populated with Teredo. Sizes of the Teredo vary depending on the size of the branch or tree trunk they are tunneling through. Seawater flushes the mangroves with 4 foot tides, exposing the trunks for a few hours each day, allowing easy access to the exposure site during low tides.
• Determining the minimum period of marine exposure to observe settlement and tunneling.
This is an exciting exploration which helps in the long term plans of developing nontoxic options to prevent Teredo damage to wood structures of economic value. Anyone interested in collaboration on basic Teredo biology or in applied research, please contact Jonathan R. Matias at the following email: email@example.com