Churning up sediments and redistributing nutrients and organic matter, burrowing marine worms are sometimes described as ecosystem engineers. But how do these creatures move through their sticky environment? Kelly Dorgan from the University of California Berkeley explains that Nereis virens burrow by driving cracks through sediments, but could other worms, which move in different ways, be doing the same? Curious to find out how pointy headed Cirriformia moorei polychaetes burrow, Dorgan and her colleague James Che collected the polychaetes from local mudflats and filmed the worms as they moved through mud-like gelatine (p. ).
Tracking the course of the front tip of C. moorei's body, the duo could see the polychaete lunge forward in four discrete phases. First the worm thinned and moved forward into the crack that had opened during the previous lunge. Having reached the end of the original crack it penetrated the fresh mud propagating the crack further. Once the worm had extended the crack as far as possible, it thickened its body, generating high stresses and widening the channel. Finally, the worm dragged the rest of its body forward into the crack as the head slipped back slightly. In essence C. moorei drives itself through the mud like a wedge cracking it apart, just like Nereis virens despite their different behaviours.
The duo also found that small C. moorei were blunter, thicker and varied their thickness more when cracking the sediments open, and despite finding it harder than larger worms to penetrate sediments, the tiddlers were faster.
Considering the effects of worm populations on marine sediment structure, Che and Dorgan also suspect that smaller worms may be better at mixing sediments while larger worms may produce more permanent structural changes.
