Abstract
The retention efficiency (RE) of suspension-feeding bivalve molluscs depends on par- ticle size and is generally assumed to decline below a maximum retention of particles larger than 3 to 7 μm. Previous suggestions that the RE spectrum of mussels Mytilus edulis can exhibit variability, possibly as a result of physiological regulation, have been attributed to artifacts associated with the indirect method. The possibility that variable physical properties of seston particles and/or miscal- culations can result in inaccurate RE measurements was examined using 3 methodologies (static, flow-through and a new approach based on the static method) and 3 particle sources (natural seston, algal cell monocultures and clay). Measurements obtained with the static method varied de- pending on the selected sampling interval. However, this artifact can be removed using frequent sampling and a regression analysis approach. Accurate RE measurements can be obtained with the flow-through method when feeding behaviour is flow independent. For all particle suspensions and methods, mussels from the study site in Lysefjord, Norway, had a maximum RE for particles >8-11 μm (1 to 5 September 2015). The RE for smaller particles declined gradually, with 50-60% retention of 4 μm particles and 30-40% retention of 2 μm particles. Differences in the RE size spectra of mussels and tunicates Ciona intestinalis, collected and measured at the same site, further indicated that RE was not influenced by potentially confounding methodological factors. Assump- tions regarding the RE spectrum of bi valves have contributed to many conclusions on their ecosys- tem interactions. The reliability of clearance rate measurements obtained using the indirect method can only be assured if the effective retention of tracer particles is confirmed and not assumed.
Highlights
Dense populations of wild and cultured bivalve molluscs can play an important role in coastal marine ecosystems through the provision of ecological services and possibly by way of negative environmental effects (Shumway 2011)
The present study examined the precision of retention efficiency (RE) measurements across the ambient particle size spectra and showed that the high variability of particle concentrations in size bins larger than 11.2 μm consistently reduced the precision of RE values for those sizes
The results of the present study showed that the RE size distribution of mussels feeding on natural seston does not always conform to the traditionally assumed model
Summary
Dense populations of wild and cultured bivalve molluscs can play an important role in coastal marine ecosystems through the provision of ecological services and possibly by way of negative environmental effects (Shumway 2011). This role is largely linked to the population’s capacity to capture suspended par-. Aquat Biol 25: 61–73, 2016 removal of particles from a set volume or constant flow In both cases, CR is a function of the rate that water is pumped through the gill (pumping rate, PR) and the proportion of suspended particles that are retained by the feeding apparatus (retention efficiency, RE). Knowledge on the relationship between RE and particle size is essential for determining accurate CRs and subsequently for interpreting ecosystem interactions with bivalve populations
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