The sea cucumber, an apparently sedentary creature, is anything but

SEA CUCUMBERS, soft-bodied relatives of sea urchins and starfish, are a sought-after foodstuff. In China alone the market for their flesh is worth $3bn a year. Unfortunately for those who try to make a living catching them, their populations often seem to undergo a cycle of boom and bust.Annie Mercier of the Memorial University of Newfoundland, in Canada, was curious to know why this is. In particular, she wondered whether over-harvesting was to blame, or if the animals were simply migrating away. As she reports in the , they not only migrate, they do so by adopting a second vegetable-like guise—that of tumbleweeds.