Marion Lake (IBP) — from Bacteria to Fish

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Abstract
The microbial–detritus food chain in the sediment of Marion Lake, British Columbia, is an important pathway for the cycling of organic matter derived from both allochthonous (leaf litter) and autochthonous (phytoplankton, aquatic macrophytes, and benthic algae) sources. The activity of the sediment microbial community (approximately 109–1010 cells/g dry wt) as estimated by oxygen consumption and solute uptake is greatest during the summer months, when water temperatures are higher than 10 C. Solute uptake is also influenced by sediment depth, nutrient enrichment, sediment particle size, and oxygen concentration. Organic matter from natural sources such as algal excretion, interstitial water, and leaf detritus is complex and is not assimilated as rapidly as the simpler organic compounds.Rainbow trout (Salmo gairdneri) and kokanee (Oncorhynchus nerka) in Marion Lake are characterized by small average size and slow growth rates. Fish production, although highly variable, is at the low end of the range compared to other salmonid producing systems. These characteristics are related to the inefficiency of trout and kokanee in cropping the benthic food supply. Experiments with individual predators and their prey have identified the nature of many of the interactions controlling the availability of benthic prey to the predators. Construction of simulation models shows promise as a means to quantify the importance of such interactions.

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