| Summary: | Deep-sea sediment can be markedly modified by the activities of the mobile epibenthic megafauna. Among other factors, the scale and rate of such bioturbations will be influenced by the population density, as well as by the pattern and speed of movement of members of such a faunal group. Any attempt to obtain an estimate of the effects of the activity of such groups on the sediment is accompanied by a number of assumptions about their individual mode of movement. We examined the degree to which these estimates depend on the assumed mode of motion. Speed and behaviour data were recovered from a free-vehicle camera for the elasipodid holothurian Oneirophanta mutabilis, a dominant component of the mobile invertebrate megafauna on the Porcupine Abyssal Plain (PAP), northeast Atlantic. Using these data, we developed a number of simulations to determine the time taken by the PAP population of O. mutabilis to cover 50% of the sediment area (t50%) by differing ranging strategies. At a hypothetical population density of 27.78 indiv. × 10−3 m−2 using a systematic search, t50% is 12 days whereas for a random ranging strategy, t50% is 17 years. A simulation incorporating observed distributions of speed and angles of turn, hence approximating the actual behaviour of the holothurian, issued a t50% of 9.6 years. The behaviour of the animal is shown to have a profound effect on areal coverage times and consequent rates of bioturbation. Simply multiplying mean speed by swath width is shown to be too simplistic an approach.
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