Xylophaga-burrows-in-wood

Micro CT scan showing burrows of the deep-sea 'shipworms' inside a piece of wood (white line scale is 30mm).

Deep-sea shipworms revealed by micro-CT scans

Micro-CT (micro computed tomography) scans of wood have revealed clues about the lives of a strange deep-sea wood-eating creature, nicknamed a shipworm, giving scientists a better understanding of the role these animals play in recycling organic matter around the globe.

The deep-sea shipworm, belongs to the group Xylophaga (Latin for ‘woodeater’) and is actually a clam (mollusc). Shipworms eat decaying wood that has ended up on the seafloor. Only the size of a pea, they have been found on these isolated deep-sea habitats all over the world.

Scientists, led by the Natural History Museum, have revealed for the first time details about the animals’ burrows, their growth rates, and how fast they eat through the wood.

The team dropped pieces of wood on the seafloor at depths of 500-5000m in the Indian Ocean, Caribbean Sea and Atlantic Ocean. Remotely operated vehicles (ROVs) were used to retrieve the wood months and years later.

The team then produced detailed images of the recovered wood using the Museum's X-ray micro-CT scanner - this captures cross-sections of an object to create a 3D virtual model.

New findings

The 3D images revealed the unique shape of the Xylophaga burrows and the growth rate of the animals - the approximate minimum growth rate of one of the species was 8.8 millimetres per year. The team says this is rapid when compared with another deep-sea clam Tindaria callistiformis that grows 8.4 millimetres every 100 years.

Wood borings of another shipworm

Wood borings of another shipworm, or Xylophaga, species (scale is 30mm).

 

They measured the speed at which the animals ate through the wood, which was up to 60 square centimetres per year per 100 individuals. ‘This was fast and expected but we have no other similar animal to compare it with,’ said Dr Diva Amon, a postdoctoral researcher at the University of Hawai’i at Manoa, who undertook the studies during her PhD work at the Natural History Museum.

Trees’ second life

'Many people never realise that tonnes and tonnes of trees that die on land have a second life down in the deep sea,' Amon adds.

When a piece of wood or even intact tree drifts out into the ocean and sinks to the seafloor, it begins a new life, transforming a usually barren-looking deep-sea floor into an oasis of activity.

Over time, a variety of unique organisms colonise the wood, known as a wood fall, and use it as a source of food and shelter. This can last for several years.

'Finding these colonies of wood borers reminds us that this significant terrestrial resource, trees, also carries on providing ecological services in the deep sea for a considerable amount of time,’ said Amon.

Remaining mystery

The team also discovered a different species of Xylophaga in each study location. This further adds to the puzzling question of how these animals find such isolated habitats in the huge expanse of the world’s oceans.

'One of the great remaining mysteries of deep ocean biology is how tiny invertebrates can disperse between isolated woody habitats on the seafloor', said Dr Adrian Glover from the Museum, a co-author of the study.

'Learning more about the basic biology of these unique organisms is crucial to answering these bigger questions.'