Burrow irrigation behavior of Urechis caupo, a filter-feeding marine invertebrate, in its natural habitat

Urechis caupo is a burrow-dwelling filter feeder that captures suspended particles in a mucus net and irrigates its burrow with peristaltic body wall contractions. An electromagnetic flow meter was used to measure the burrow irrigation rates of 7 U. caupo in their natural burrows under normal tidal cycles. The average burrow irrigation rate of 266 ± 158 ml min–1 (mean ± SD) was much greater than that typically reported in laboratory studies (10 to 50 ml min–1). Periods of high irrigation activity, which probably corresponded to feeding behavior, represented 33% of the recorded behavior. These events each lasted for 13.8 ± 4.1 min (mean ± SD), during which time the average irrigation rate was 440 ± 160 ml min–1 (mean ± SD) with a maximum sustained rate of 870 ml min–1. The mean pumping frequency (5.8 contractions min–1) was similar to that of laboratory studies, while the mean stroke volume (44 ml) was comparatively high, indicating that increased stroke volume produced the high flow rates observed in our study. Based on previous density estimates (61 m–2), the data suggest that a population of U. caupo in 1 m2 of mudflat can collectively pump 23 000 l water d–1 through their burrows, of which 13 000 l is filtered through the mucus net.