The effect of increasing laminar flow speed on Vorticella convalleria orientation

Microscopic sessile suspension feeders (MSSFs) are unicellular protists that live attached to surfaces in aquatic ecosystems. They create a fluid flow using a ring of cilia or flagella, and this flow draws in their food. They feed on bacteria, phytoplankton, and small detritus. They therefore contribute to the carbon cycle and potentially to biological restoration after human-caused biological harm such as oil spills. Their feeding flow and feeding rates are determined by ambient environmental flow and how the organism is orientated in relation to the flow. Previous work has found that in unidirectional flow, when the cell body is orientated pointing into the flow, MSSFs have a higher feeding rate. When the cell body is pointed in the direction of the flow, the feeding rate is lower, and the full 3D orientation is needed to determine feeding flows and feeding rates. Further, Vorticella convallaria, a common MSSF, have been found to be reorientated by ambient flow. In slow unidirectional flows (corresponding to cm/s freestream flow in a stream or river), these organisms were pushed towards unfavorable orientations for feeding, but were still able to actively reorient the cell body. We hypothesize that at higher ambient flow speeds the organism may be unable to reorient, leading to a lower feeding rate. To test this hypothesis, we observed Vorticella in unidirectional flow in a flow channel using simultaneous top and side view to determine 3D orientation.