OSOVITZ, C. J.*; JULIAN, D.: Burrow Irrigation Rate of Urechis caupo in Its Natural Habitat

Burrow dwelling filter feeders pump large amounts of seawater through their burrows for nutrition and respiration. In our study, we determined how much water is pumped by the echiuran worm Urechis caupo in its natural habitat. U. caupo‘s burrow irrigation rate has been well studied in the laboratory, but it has never been studied in the animal’s natural environment. Previous laboratory studies have reported irrigation rates from 14 to 45 ml/min (26 ml/min average), but in one study, J&oslashrgensen (1986) reported an irrigation rate of 213 ml/min, which is 8 times higher than the values reported by all other researchers. We measured the irrigation rates of four natural U. caupo burrows using a non-restrictive electromagnetic flow probe. One relatively inactive worm pumped only 42 ml/min, but the other worms’ pumping activity averaged at least 190 ml/min. The average flow rate for all worms was 140 ml/min. Due to the unexpectedly high pump rates of two worms, the sensitivity of the flow device (300-550 ml/min) was occasionally exceeded, meaning the true average pump rate must be even higher. The average frequency of pumping (3.6/min) was similar to previously reported laboratory values, but the average stroke volume was four-fold higher. Therefore, the high pump rate observed in this study is primarily a product of a higher stroke volume than that observed in laboratory studies. We observed frequent periods of high activity that resembled prior descriptions of feeding behavior. These typically exceeded 300 ml/min, which is at least 9 times higher than the average reported value for feeding behavior in the laboratory. These results emphasize the importance of field measurements to describe natural phenomena and demonstrate a need to reexamine the ecological impact of U. caupo on its environment.