Ambient flow velocity and resulting clearance rates of the terebellid polychaete Lanice conchilega (Pallas, 1766)

Abstract

A laboratory flume study was conducted to determine the effect of flow velocity on clearance rates of the Polychaeta Terebellidea Lanice conchilega (Pallas, 1966). Using sets of 75 individuals collected along the east coast of the English Channel, we measured clearance rates at five flow velocities of ≈4, 9, 15, 22 and 27 cm s − 1 with a culture of the diatom Chaetoceros calcitrans as food source. During each control (without polychaetes) or clearance (with Lanice conchilega) experiment, in vivo fluorescence was continuously monitored. Further HPLC analysis confirmed the sediment resuspension for the highest flow velocities tested, indicating the need for 'corrections' from control experiments. The global pattern resulted in a dome-shaped curve, with a corrected clearance rate per individual increasing with flow velocity from an average value of 0.091 ± 0.041 L h − 1 gDW − 1 at 4 cm s − 1 up to a maximal value of 0.171 ± 0.046 L h − 1 ind − 1 at 15 cm s − 1 and decreasing for higher flow velocity (0.063 ± 0.029 L h − 1 ind − 1 at 27 cm s − 1 ). When normalised to average Dry Weight (DW), the clearance rates varied in a wider range, with maximal clearance rates of up to 0.749 L h − 1 gDW − 1 and a marked dome-shaped structure for small individuals (11.9 ± 5.4 mg Ash Free Dry Weight), whereas larger individuals (up to 30 mg AFDW) showed maximal clearance rates of around 0.400 L h − 1 gDW − 1 . Our results indicate the need to take flow velocity into account in estimating the ecological impact of filter-feeding polychaetes on available food, as large budget underestimates may arise from clearance rates measured in non-controlled flow velocity.