Threat to landscape from alien crayfish?

The stealthy invasion of rivers in Europe by the tasty American signal crayfish Pacifastacus leniusculus poses a threat not only to the indigenous European species Astacus astacus (P. leniusculus carries a fungal infection as well as being formidably armed), but conceivably to the very landscape itself (Johnson, M.F. et al. 2010. Topographic disturbance of subaqueous gravel substrates by signal crayfish (Pacifastacus leniusculus). Geomorphology, v. 123, p. 269-278). Johnsson and colleagues from the University of Loughborough, UK used captive alien crayfish to model the effects of their bioturbation under controlled laboratory conditions, assessing their activity by the use of millimetre-resolution gravel-surface elevation data generated by a laser altimeter. The sturdy little beasts behave like frenzied bulldozers creating mounds and pits in the gravel substrate, displacing on average about 1.7 kg of gravel every day over an area of 1 m2 thereby completely disrupting the perfectly flat substrate onto which they were introduced in about 3 days. By this activity they render the surface more prone to erosion by flowing water so that greater grain transport ensues; they could effect bother erosion and deposition by increasing transportation of grains. To my knowledge, this is the first experimental study of bioturbation in the context of hydrology. We can expect more now that the technology is available: the burrowers as well as the diggers of the animal world. While the Phanerozoic is best know for having begun with the Cambrian Explosion of multicellular life, a sometimes overlooked attribute is that it coincided with the start of bioturbation. That may well have had a profound effect on sediment transport as the American invader suggests.

See also: Newton, A. 2010. Crayfish at work. Nature Geoscience, v. 3, p. 592

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