Particle size, flow speed, and body size interactions determine feeding rates of a solitary ascidian Styela plicata: A flume experiment

Abstract

Benthic suspension feeders are a primary conduit for the transfer of carbon from the water column to the benthos. As such, factors that influence their feeding require mechanistic study and quantification. In this flume experiment, the clearance rate of the solitary ascidian Styela plicata varied as a function of flow speed, body size, and particle diameter. At all flow speeds and body sizes tested, clearance rates increased directly with particle diameter to ~10 μm. As particle diameter increased further to ~32 μm, clearance remained constant or declined depending on flow speed. At 3 and 22 cm s-1, clearance remained constant with particle diameter >10 μm. At 14 cm s -1, clearance sharply declined as particle diameter increased above 10 μm. In general, clearance rates increased with body size across all particle diameters. However, allometric exponents relating clearance rate to body size, which ranged from 0.28 to 0.62, were lower than expected (~0.67) due to the confounding effects of water flow, to which clearance rate responded in a non-linear fashion. We fit our measurements to a 3-dimensional surface that relates clearance rate, body size, and flow speed. These surface fits show that clearance of small particles (<10 μm diameter) was maximal at intermediate flow speeds (~12 cm s-1) and decreased at both faster and slower flow speeds. This 'unimodal' response is consistent with predictions of suspension-feeding theory. In contrast, clearance of large particles (>10 μm diameter) decreased steadily as flow speed increased from 3 to 22 cm s-1. © Inter-Research 2014.