Laboratory measurements of dissolved oxygen (DO) uptake by Glossosoma nigrior Banks were conducted in a sealed, recirculating flume under variable fluid flow velocities. Measurements were performed in similar water temperatures, DO concentrations and fluid flow velocities to field conditions in the stream where the larvae were obtained. Total oxygen uptake by both cased larvae and corresponding cases without larvae were quantified. An increased fluid flow velocity corresponded to an increased larval DO uptake rate. Oxygen uptake by the larval cases alone was not as sensitive to changes in the Peclet (Pe) number, the dimensionless ratio of advective to diffusive DO transport, as uptake by larvae themselves. The flux of DO to larvae and their cases was up to seven times larger in a moving fluid in comparison to non-moving fluid conditions in the proximity of larvae for 0>Pe>175. A functional relationship was developed relating fluid flow and DO uptake across a larval case. According to the proposed quantitative relationship, Pe alone describes 91% of the variation in the DO flux to the larvae under variable fluid flow conditions. In response to fluid motion, larvae depicted two characteristic behavioral responses. When the ratio of advective DO transport to diffusive transport was low (Pe>87), larvae occasionally abandoned their cases or spent more time partially extended from their cases. At Pe<87, larvae typically remained in their cases. This indicates that oxygen delivery to the larvae at low Pe is insufficient to satisfy the respiratory demands of cased larvae.
- Discharge velocity
- Dissolved oxygen