The population energetics of two species of amphipods was studied at several depths in Marion Lake, BC. Hyalella azteca was abundant at a depth of 1.0 m, (mean summer standing crop, 1952 animals/m2 but became rare (75 animals/m2 at depths greater than 2.5 m. Growth rates, res- piration rates, and hence energy flow were decreased by the lower ambient temperatures of deeper water, On an annual basis, a mean standing crop of 1.1 Kcal/m2 of Hyalella assimilated 18.1 Kcal/m2 respired 14.1 Kcal/m2 and used 4.0 Kcal/m2 in production of growth, molts and eggs, Approximately 3/4 of the annual energy flow was completed between June and October, The ecological efficiency of Hyalella populations was 10, the net production efficiency, 22%, and the net population growth efficiency, 12%-13%, The mean summer density of Crangonyx remained constant with depth (about 249 animals/m2). Annual energy flow and production were not appreciably affected by lower temperatures in deeper water. On an annual basis, a mean standing crop of 0.7 Kcal/m2 assimilated 7.7 Kcal/m2 respired 6.3 Kcal/m2 and used 1.4 Kcal/m2 in production Crangonyx energy flow was fairly constant throughout the year. The ecological efficiency of Crangonyx was 8%, the net production efficiency, 17%-19%, and the population growth efficiency, 14%-15%. Annually, Hyalella populations assimilated only twice as much and produced about 3 times as much energy as did Crangonyx populations, but during the summer, Hyalella energy flow was 4 times that of Crangonyx. A synthesis of existing data on poikilotherm energetics suggests that life history phenomena are important in determining the relationship between annual population respiration and production. Also, annual production and assimilation were found to be closely related to the mean standing crop of various organisms. / Science, Faculty of / Zoology, Department of / Graduate

Meiofaunal distribution and abundance were studied in Marion Lake, a small, shallow (8m maximum) oligotrophic lake in southwestern British Columbia. Experimental techniques were used to investigate the influence of food and predation on meiofaunal populations, and to estimate relative carbon -flow to all components (micro-, meio-, and macrofauna) of the zoobenthic community. In two years' sampling of over 50 species of meiofaunal rotifers, nematodes, copepods, cladocerans and halacarine mites, only a few species were abundant. Three depth zones were sampled (1.0, 2.5, 4.5m) and maximum densities occurred at 2.5m. Population densities of all groups were stable over the sampling period, fluctuating less than one order of magnitude annually. In culture studies, representative meiofaunal species had longer generation times and lower reproductive rates than expected. Attempts to use laboratory results to predict field population dynamics were generally unsuccessful, but led to clarification of reproductive parameter estimates. Experiments in the laboratory and in the field suggested that meiofaunal species are not food-limited. Predation on meiofauna is not heavy but might be significant for those species whose reproduction is suppressed by adverse temperatures. Radiotracer experiments indicated that carbon flow to the zoobenthic community from sediment microflora was partitioned approximately 12% to microfauna (ciliates), 12% to meiofauna, and 76% to macrofauna, while the contributions to zoobenthic biomass were 1%, 7% and 92% respectively. In related experiments, a common harpacticoid copepod species had a high assimilation efficiency but rapidly respired and excreted recently ingested carbon. Meiofaunal organisms are apparently not an important food source for higher trophic levels in Marion Lake but may play a significant role in stimulating microfloral production by their grazing activity. / Science, Faculty of / Zoology, Department of / Graduate