More on Bone Eating Sea Worms

As I mentioned in a previous post some sea worms feed on whale bones. BBC News is reporting some have been discovered off the coast of Sweden (they were previously known only off the coast of California).

above is a picture of the Swedish species. Below is a scanning electron micrograph of the sea worm.

Here is another picture:

Here is what is know, so far:

Osedax worms are about 1-2cm in length.

A scanning electron micrograph shows up remarkable detail in the North Sea worm
They root themselves to the whale bones which they then plunder for oils with the help of symbiotic bacteria. The worms’ flower-like plumes pull oxygen from the water.

There is a mystery:

Their reproductive system is extraordinary – certainly in the case of the Pacific Osedax.

“The female Pacific worms keep males inside their tube as a sort of little harem that fertilises eggs as they are released into the water column,” explained Dr Glover.

“We’re not sure what’s happening with the reproductive biology of the Swedish worms yet. We’ve only got females; we haven’t found any males. It’s a bit weird.”

Scientists have established that all of the Osedax species so far identified appear to be closely related to vestimentiferan tubeworms, which are found only at the volcanic cracks in the ocean floor called hydrothermal vents.

There is also a fly in the ointment. Since these worms live on whale falls (I. E. carcasses of dead whales that sink to the ocean floor) it is believed that whale carcasses act as stopping points that allow organisms to move around the ocean floor. If whales have low population numbers or are extinct this “island hopping” can’t work:

What concerns researchers is that the commercial hunting which so devastated whaling populations would also have severely curtailed this activity by reducing the incidence of whale fall.

It may even have led to the extinction of some bottom-dwelling organisms that depended on this rare but concentrated nutrient supply.

Bone Eating Sea Worms

Below is a picture of a type of polychaeta belonging to the genus Osedax. They were recently discovered feasting on the skeleton of a juvenile grey whale. This ability of Osadax species to feed on skeletal material is quite interesting and – heretofore – unknown.

According to a recent article in Environmental Microbiology this is how it works. Like a some other sea worms (such as red tube worms)Osedax lack a mouth and functional gut. They also, unlike other sea worms, lack a trophosome (an internal organ that houses endosymbionts – sea worms with trophosomes derive nutrition from the endosymbionts).
Instead, Osedax species have a highly vascularized root system (r in the righthand picture above) that invades the bone marrow. The root system is connected to a large eggsac (o in the righthand picture above). Both eggsac and root system are filled with bacteriocytes. This is where the story gets even more interesting. Normally, the bacteria found in most sea worms are autotrophic, that is, they produce their own food. Osedax bacteria, on the otherhand, are hetertrophic. The way the symbiotic relatonship was established makes for fascinating reading and I strongly recommend you follow the link and read for yourself (you should probably reread my posts on stable isotope analysis first).