Bioturbation

In oceanography and limnology, bioturbation is the displacement and mixing of sediment particles by benthic fauna (animals) or flora (plants). The mediators of bioturbation are typically annelid worms (e.g. polychaetes, oligochaetes), bivalves (e.g. mussels, clams), gastropods, holothurians, or any other infaunal or epifaunal organisms. Faunal activities, such as burrowing, ingestion and defecation of sediment grains, construction and maintenance of galleries, and infilling of abandoned dwellings, displace sediment grains and mix the sediment matrix. The sediment-water interface increases in area as a result of bioturbation, affecting chemical fluxes and thus exchange between the sediment and water column. Some organisms may further enhance chemical exchange by flushing their burrows with the overlying waters, a process termed bioirrigation. Benthic flora can affect sediments in a manner analogous to burrow construction and flushing by establishing root structures. Bioturbation is a diagenetic process and acts to alter the physical structure, as well as the chemical nature of the sediment.

Evolutionary significance
Bioturbation's importance for soil processes and geomorphology was ﬁrst realised by Charles Darwin, who devoted his last scientiﬁc book to the subject (The Formation of Vegetable Mould through the Action of Worms, 1881). Modern research has provided further insight into the evolutionary and ecological role of bioturbation. In modern ecological theory, bioturbation is recognised as an archetypal example of ‘ecosystem engineering’, modifying geochemical gradients, redistributing food resources, viruses, bacteria, resting stages and eggs. From an evolutionary perspective, recent investigations provide evidence that bioturbation had a key role in the evolution of metazoan life at the end of the Precambrian Era.