Hydrodynamic habitat influences suspension feeding by unionid mussels in freshwater ecosystems

Abstract

Summary Benthic suspension feeders play significant roles in aquatic ecosystems, but the influences of abiotic, especially hydrodynamic, factors on many of their activities remain largely unknown. This is especially true for freshwater unionid mussels, which are important inhabitants of rivers and lakes, often forming multispecies assemblages in the former. Our goal is to determine whether and how seston flux affects the suspension feeding of freshwater unionid mussels from different hydrodynamic habitats (i.e. lentic and lotic). Fluorometric measurements of algal depletion in a recirculating flow chamber were used to determine the clearance rate (CR) of four freshwater mussel species: Elliptio complanata, Elliptio dilatata, Fusconaia flava and Strophitus undulatus. Clearance rate varied with algal flux (J = UC, where U is velocity and C is algal concentration) for all species examined, resulting in a 41‐fold increase in CR for some species, compared with no‐flux controls. Importantly, the results from the no‐flux controls were consistent with published CR values obtained under static conditions. Elliptio dilatata from the fastest flowing lotic system (Grand River, Ontario) cleared up to four times more algae than any other species, including its conspecifics from a slower flowing river (Ausable River, Ontario) and the species from the lentic habitat (E. complanata; Lake Opeongo, Ontario). Differences in CRs were also found among E. dilatata, F. flava and S. undulatus from the same lotic habitat at the highest algal flux examined, indicating that species may specialise to different hydrodynamic conditions. The impact of suspension feeding by unionid mussels has probably been underestimated, especially under lotic conditions with high seston flux. Mussels may have ecotypic responses to their hydrodynamic habitats, which affect their CR. Moreover, specialisation within a single habitat type is indicative of resource partitioning that could reduce competition in multispecies assemblages.

Algal flux affects the clearance rates of recently metamorphosed freshwater mussels

“…For example, the CR of L. nasuta (216 ± 2 lm) were higher across flux and no-flow conditions than those of L. fasciola with larger shell lengths (285 ± 2 lm). These findings indicate that the species specific differences in the CR abilities reported in adult mussels (vanden Byllaardt and Ackerman 2014) are also evident in recently metamorphosed juvenile mussels.…”

“…fine POM and phytoplankton downstream) on which they have specialized (Hudon 2000). This hypothesis may be difficult to resolve, however, because differences in substrate and water velocity also change with position in a watershed (Vannote et al 1980), which overlaps with the microhabitat hypothesis; and (4) niche separation, whereby mussel species maybe specializing on different seston components and/or flux (Ackerman and Nishizaki 2004;vanden Byllaardt and Ackerman 2014). Given that all the species were found in rivers, the morphology hypothesis does not apply.…”

Drought‐induced changes in flow regimes lead to long‐term losses in mussel‐provided ecosystem services

“…Marine bivalves and zebra mussels have higher clearance rates in flowing water than under static conditions (Wildish and Kristmanson ; Ackerman ; Elliott et al. ), and this has been recently documented for freshwater mussels (Vanden Byllaardt and Ackerman ). Our estimates are also conservative because we only quantified effects of mussels living in large beds and ignored effects of sparser mussel occurrences between beds.…”

Does size matter? Particle size vs. quality in bivalve suspension feeding

“…The mussels were transported in aerated coolers partially filled with river water and 5–10 cm of river sediment to the Hagen Aqualab (University of Guelph, Ontario) where they were transferred into 50–60‐L flow‐through chambers with 24‐hr residence time of well water. They were maintained for up to six weeks on 0.17 mL of concentrated, preserved microalgae (Shellfish Diet and Nanno 3600; Reed Mariculture Inc, CA) that was added to the flow‐through water daily (10 3 cells/L within the chamber; McNichols et al., ; vanden Byllaardt & Ackerman, ; Tremblay, Morris, & Ackerman, ). Prior to experiments mussels were maintained without food for three days to reduce incidents of non‐feeding (Atkinson, First, Covich, Opsahl, & Golladay, ; Beck & Neves, ; Silverman et al., ).…”