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

Abstract

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 behav- ior. These events each lasted for 13.8 ± 4.1 min (mean ± SD), during which time the average irriga- tion 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 pro- duced 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 m 2 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.