Küstenbiologie - Coastal Biology

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Shipworm biology shipworm lifecycle

shipworm lifecycle

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Life starts for Teredo navalis after internal fertilization as a typical bivalve larva inside its mothers gill chamber. Here it can after a „placental reaction“ be nourished by its parent and grows to the veliger stage and a size of about 70 µm. Together with thousands or up to 2 million siblings tha larva is expelled to find a new environment, i.e. a new piece of wood.

The trip takes two or three weeks and depends on the surrounding water currents. Like many other mollusc larvae Teredo lives on a diet of microalgae. In fact it is almost indistiguishable from other bivalves at this stage.

Once the larvae is „ripe“ for settlement, it can locate logs by „smelling“ decomposing wood and actively swimming the last few centimeters. It crawls with its foot on the surface to find a suitable location, where it attaches itself with a single byssus strand. Now starts a rather miraculous boring action. The larval shell is not calcified and therefore quite soft, so that it cannot be a functional borer. Instead it is speculated that the larva can soften wood with the aid of maternal enzymes and then excavate a small hole with its foot. In there Teredo metamorphoses to its adult shipworm form.

A shipworm cannot ever leave its hole, being connected to it close to the opening. It bores and grows into the wood. The opening is extended only slightly (up to ca. 1 mm diameter) during the lifetime of two to three years, but the tunnel grows in diameter from a millimeter to about pencil size. It is perfectly circular due to the circular rasping motion of the shell and usually extends to 20 or 30 cm length. However, the longest tunnel ever recorded was 62 cm long! And that was not in a warm water region, but in the Kattegat between the North Sea and the Baltic.

The shipworm starts as a male, producing sperm after a few weeks, with a size of only a few centimeters. Afterwards it changes its gender and starts female reproduction. This depends largely on water temperature and food availability of an uncrowded supply of wood and proper additional diet of planktonic microalgae, which it filters from the water like any other bivalve. With optimum conditions an enormous amount of egg cells is produced. Sperm is taken up from neighbouring shipworms, followed by the mentioned internal fertilization. However, if no male specimen is located nearby, Teredo can fall back to its own sperm from the male life stage.
Still, the life cycle does not end here. Mrs. Teredo changes back to male and to female again afterwards. In warmer waters it can achieve several reproduction cycles per year, but this is quite unlikely to happen in the Baltic Sea.

Last Updated on Friday, 21 January 2011 22:01  

newsflash!

Teredo is back in numbers!

Not the expected 2009, but 2010 was another record year for teredo settlement. A total of 19.600 larvae / m2 was recorded for untreated pine blocks. This is the third highest number since 1997.

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