How fast do marine invertebrates burrow?

The burrowing of bivalves, arthropods, and echinoderms collected from tidal flats and shallow subtidal sediments of the Ogeechee estuary, Georgia, U.S.A was analyzed using time-elapse, X-ray analysis of thin-walled aquaria. The rate of sediment intrusion was determined for each animal. Burrowing rates ranged between 0.01 and 0.15 cm3/h for suspension-feeding animals. Deposit-feeding animals moved between 1 and 10 cm3 of sand per hour, approximately 10 to 100 times more sediment than the suspension feeders moved over similar times.Neoichnological experiments show that ten filter-feeding individuals could take as long as 115 yr to churn a 1 m2 plot of sediment, by indexing the measured burrowing rates to realistic animal population densities. Ten such mobile deposit feeders as irregular echinoderms could bioturbate the same sediment in just 42 days. Under the maximum population densities modeled, the animals could bioturbate the sediment plot in 61 min. Given the reported results, qualitative interpretation of the rock record is possible: highly burrowed examples of the Skolithos Ichnofacies reflect high population densities and at least seasonal time spans. Highly burrowed examples of the Cruziana Ichnofacies may represent moderate population densities and short time spans.