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Inter-relationships between a deposit-feeding amphipod and metabolism of sediment microflora Hargrave, Barry Thomas

Abstract

The food of a common freshwater deposit-feeding amphipod Hyalella ctzteca (Saussure) and the effect of its feeding on energy transfer within the sediments of Marion Lake were examined. By use of C¹⁴ labelling techniques and chemical analyses of food and faeces, Hyalella was shown to digest algal and bacterial cells from ingested sediment particles at a rate sufficient to supply energy necessary for observed growth, respiration and egg production. Non-living sediment organic substances (cellulose and lignin-like materials) were not assimilated. Changes in oxygen concentration over undisturbed sediment cores incubated under light and dark conditions and with antibiotic additions were used to provide an in situ measure of epibenthic algal production and community and bacterial respiration. Seasonal and spatial differences in sediment microflora production potentially available for consumption by Hyalella were positively correlated with amphipod growth, distribution and the onset of egg production. In laboratory experiments amphipods selected sediments with the highest concentrations of microflora and growth was proportional to the abundance of this food source. Numbers of Hyalella were varied in undisturbed sediment cores to evaluate the effect on microflora production. After 43 hr incubation, algal production stimulated at natural amphipod densities and declined, with higher numbers. Lacterial respiration was stimulated at densities four times those observed in Marion Lake and this also decreased with crowding. Total microflora production and amphipod energy requirements were compared to calculate that at natural densities during the summer Hyalella would consume less than 10% of the daily production. The remaining microflora production may be consumed by numerous other deposit-feeding species in the benthic community. Physical leaching and heterotrophic organisms lowered the organic content of faeces in the dark, while autotrophic organisms and dissolved organic compounds released by amphipods added organic matter to faecal pellets. Thus, while Hyalella's browsing activities may reduce the biomass of sediment microflora, it concurrently aided recolonization of faecal material and sediment particles and thus appears to stimulate production of its own food supply. Additional data are presented which compare the respiration of different benthic communities. The similarity of the rates of oxygen exchange, after correction for temperature difference, suggests that processes affecting oxygen availability are important in determining the overall rate of energy transfer within many benthic communities.

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