BIOTURBATION

Charles Darwin (1881) first established the importance of burrowing land animals, such as earthworms, in the mixing of the uppermost layer of the soil. A similar mixing effect may be seen on coastal mud-flats resulting from the activities of burrowing animals, such as the lugworm Arenicola, which creates a micro-landscape of pits and volcano-like faecal mounds (Fig. 14.1) as a result of its sediment swallowing lifestyle. In recent years it has been shown that the activities of the benthos of shallow soft bottoms profoundly affect sediment properties and processes (Johnson, 1971; Rhoads, 1974; Rhoads & Boyer, 1982; R. C. Aller, 1982; Meadows & Tufail, 1986).

In the deep sea, because benthic standing stock may be several orders of magnitude less than in productive inshore areas, and individual benthic animals are generally of much smaller size, it might seem that such effects will be of only minor importance. Furthermore, it has been thought that rates of biological processes are much lower in the deep sea. Against this, it can be argued that deposit-eating forms dominate by far over suspension feeders and may be adapted towards more complete utilization of organic materials (e.g. longer guts). Because of decreasing hydrodynamic energy and rate of sedimentation, there should also be less frequent re-suspension of sediment and hence less disruption of biogenic structure; and, because of the low rates of sedimentation, such biogenic structure should persist much longer than in shallow water (Rowe, 1974).