Abstract
Behavior of the common lancelet Branchiostoma japonicum in sediment and effects of their turbation on sediment were observed in a tank to discover their ecological significance in a sandbank with a dense population of the animals. Direct observation using a video camera revealed that a lancelet frequently moves in the sediment only a short distance (a few centimeters at most) over the course of a day and rarely swims out from the sediment, and only for a few seconds. Sand ridges 4 cm high formed in the tank with lancelets at a density of 560 animals m-2 became almost level during an incubation period of 10 days, in contrast to a tank without lancelets, where there was no change. Dissolved O2 concentration in the interstitial water of the sediment with lancelets was 2-5 times higher than that without lancelets at the end of incubation for 7 or 12 days. These results indicate that bioturbation by a dense population of lancelets has significant effects on the physical and chemical conditions of the sediment.
