Flow, Flux, and Feeding in Freshwater Mussels

Abstract

Unionid mussels are important constituents of aquatic systems that are affected by anthropogenic changes in hydrology and concomitant increases in suspended solids, yet little is known about the effects of flow on their suspension feeding. We examined the clearance rates (CRs) of four species of freshwater mussels (Lampsilis siliquoidea, Lampsilis fasciola, Ligumia nasuta, and Villosa iris) to determine whether they feed selectively on river seston and how this may vary with algal flux (concentration × velocity). The CR for the Lampsilis species was also determined using seston particle size, particle fluorescence, and algal taxon. The CR of all species increased linearly with flow chamber velocity, but exhibited saturation‐like kinetics with increasing algal flux. The CRs of Lampsilis species were higher for larger (>10 μm) versus smaller (<10 μm) particles, the latter of which were numerically dominant in river seston. The CR of Lampsilis mussels on most of the algal taxa declined (linearly or nonlinearly) with algal flux indicating that mussels have reduced ability to discriminate among algae at higher flux. This potential feeding limitation could affect mussel growth and survival and make unionids vulnerable to the aforementioned hydrological changes. Ecologically, differential use of algal taxa under different algal flux indicates selective feeding, which may be evidence of resource partitioning for mussel species that occupy the same rivers. The differential use of algal taxa under different algal flux within a mussel species indicates the complex nature of bivalve feeding, their habitat requirements, and their vulnerability to human impacts.

Living the high turbidity life: The effects of total suspended solids, flow, and gill morphology on mussel feeding

“…Aeration, through an air stone mounted in the bottom of the funnel, was used to maintain the sediment suspensions and a mesh platform placed in the center of the funnel chamber was used to hold one mussel; and (2) A recirculating flow chamber (1.70 m long × 0.17 m wide channel with 0.16 m diameter × 0.16 m deep sediment compartment centered at 1.43 m downstream; see vanden Byllaardt and Ackerman ) filled with 14.5 L of experimental suspension (0.04 m water depth) was used for experiments involving TSS and water velocity. The flow chamber was designed to provide suitable conditions for the examination of suspension feeding in benthic organisms (e.g., low volume, flow conditioning and entrance length for boundary layer development and fully developed flow, large width to depth ratio to minimize secondary flows, and minimal flow obstruction of channel by organism; Nowell and Jumars ; Ackerman ; Mistry and Ackerman ). Two mussels were placed with sediments in the sediment compartment, with ~ 1 cm of their shell protruding into the flow (Mistry and Ackerman ).…”

“…The flow chamber was designed to provide suitable conditions for the examination of suspension feeding in benthic organisms (e.g., low volume, flow conditioning and entrance length for boundary layer development and fully developed flow, large width to depth ratio to minimize secondary flows, and minimal flow obstruction of channel by organism; Nowell and Jumars ; Ackerman ; Mistry and Ackerman ). Two mussels were placed with sediments in the sediment compartment, with ~ 1 cm of their shell protruding into the flow (Mistry and Ackerman ).…”

“…Despite the potential interactive effects of sediment and velocity, water velocity has not been included in the examination of the effect of TSS on CR—rather experiments are typically conducted under static conditions in aerated chambers (e.g., Foster‐Smith ; Lei et al ; Tokumon et al ; Tuttle‐Raycraft et al ). The relationship between TSS and velocity is also relevant because unionid CR increases with increasing velocity (vanden Byllaardt and Ackerman ; Mistry and Ackerman ), as do freshwater dreissenids (Ackerman , ) and marine bivalves (Wildish and Kristmanson ; Ackerman and Nishizaki ). Particle flux (i.e., J ; particles per unit time and area), which provides a manner in which to combine concentration ( C ) and velocity ( U ) as a single variable ( J = UC ), has been used to examine the CR of bivalves (i.e., vanden Byllaardt and Ackerman ; Mistry and Ackerman , ).…”

“…The relationship between TSS and velocity is also relevant because unionid CR increases with increasing velocity (vanden Byllaardt and Ackerman ; Mistry and Ackerman ), as do freshwater dreissenids (Ackerman , ) and marine bivalves (Wildish and Kristmanson ; Ackerman and Nishizaki ). Particle flux (i.e., J ; particles per unit time and area), which provides a manner in which to combine concentration ( C ) and velocity ( U ) as a single variable ( J = UC ), has been used to examine the CR of bivalves (i.e., vanden Byllaardt and Ackerman ; Mistry and Ackerman , ). A strong relationship between the CR of both juvenile and adult unionids and increasing algal flux has been found (vanden Byllaardt and Ackerman ; Mistry and Ackerman , ).…”

“…Particle flux (i.e., J ; particles per unit time and area), which provides a manner in which to combine concentration ( C ) and velocity ( U ) as a single variable ( J = UC ), has been used to examine the CR of bivalves (i.e., vanden Byllaardt and Ackerman ; Mistry and Ackerman , ). A strong relationship between the CR of both juvenile and adult unionids and increasing algal flux has been found (vanden Byllaardt and Ackerman ; Mistry and Ackerman , ). This relationship followed a unimodal pattern, similar to a type II functional feeding response (Holling ), in response to increasing algal flux (vanden Byllaardt and Ackerman ; Mistry and Ackerman ).…”