No abstract

ABSTBACT Improvedvalues of respiration and growth have been determined for three tubificid species. Maintaining the same individuals in mixed species culture before or after maintaining them separately lowered respiration by about a third, whereas lowering the population density of a single species had no such effect. The presence of Peloscolex m&tisetosus increased the weight gain of Tubifex tubifex and Limnodrilus hoffmeisteri by a factor of 2-3 times that in pure culture in a 6-month period, although the first species seemed to remain unaffected.More energy was used for growth plus respiration when the three species were mixed than when maintained in pure culture. Attempts to measure ingestion and egestion were handicapped by failure to demonstrate a reduction in percent organic matter, percent nitrogen, or caloric content in feces as opposed to the mud presented as food; this indicates selective feeding. Further, variation in defecation rate was noted, which complicates the measurement of material cycling. The study suggests that the attempt to recreate energy or material budgets for communities from laboratory studies of isolated components is less promising than the attempt to study communities in situ. INTBODUCTIONThe study of production of tubificid oligochaetes is hampered by the fact that the age of individuals cannot be determined, and life histories are not strictly regulated seasonally so that cohorts cannot be recognized.Ivlev ( 1939) surmounted this problem by determining growth and the reduction in energy in food on passage through the gut. Teal ( 1957) used scanty data on growth and respiration to determine production of Limnodrilus hoffmeisteri. Despite the current interest in production studies there are no other published data on the production of tubificid species so far as we are aware, We have attempted to obtain data on respiration, growth, ingestion, and cgcstion to solve the balanced energy equation for the three species that dominate Toronto Harbor (Brinkhurst 1970 crction of fluids or by secretion of, say, mucus. As these losses cannot be ignored, we wished to obtain values for the othe:r parameters rather than simply solve the energy equation for ingestion by difference. Other studies involved atte.mpts to follow interactions between worms and bacteria ( Wavre and Brinkhurst 1971.) and to quantitate fecal production (Appleby and Brinkhurst 1971).As an earlier laboratory study of worm populations suggested interspecific interactions between two of the three species found here ( Brinkhurst and Kennedy 1965), we investigated the effect of working with mixed as well as single species cultures. METHODS RespirationWorms were taken from Hanlan's Point, Toronto Harbor, in 4-5 m of water with an Ekman grab and sieved in the field in a wash bucket of 0.5-mm pore size to eliminate the smallest worms. The residues were placed in buckets with lake water, returned to the laboratory, and stored in environmental rooms at 5, 10, 15, and 2OC for at least 3 weeks. Worms were then sorted with Pasteur p...

The KB corer has many advantages over other bottom-sampling devices including some other coring tubes. It may be used to obtain reliable estimates of the standing stock of benthic invertebrates inhabiting soft sediments and of their spatial distribution in lakes and rivers. It may also be used for studies of the vertical distribution of animals and bacteria, and could be used for a wide variety of studies on sediments. Multiple-unit versions have been built and operated, thus overcoming the size limitation imposed by the basic design. This paper communicates some results obtained using this sampler.

Eight heterotrophic aerobic bacteria were identified in samples from Toronto Harbour. The three tubificid species present seem to ingest most if not all of these, but different species survive passage through the gut. One of the three worm species absorbs amino acid from solution in the absence of bacteria in the gut. It is suggested that the results indicate differences in the utilization of the potential nutritional resources by the worms, which may be reflected in the ability of three unspecialized sediment feeders to coexist in the same microhabitat.

Cycling of glucose at the sediment–water interface was determined through coupling measurement of natural substrate concentrations with heterotrophic uptake by the natural microbial communities in the sediment and in the water column. The same general pattern was found for both polluted and less polluted parts of Toronto Harbour, so that other labile organic species possibly have similar cycles. Velocity of uptake of glucose (flux) and turnover time showed no relationship to either substrate concentration or total organic matter of the sediments. Activity in the water column could be supported to a major extent by sediment export of substrate by turbulent diffusion. Sediment activity must be supported by particulate sedimentation and hydrolysis of large organic molecules, which may be aided by the macrobenthic community. Pollution stress apparently alters the catabolism of the substrate. The observed substrate concentrations may reflect a minimum of residual concentration, below which the microbial community has difficulty in taking up the substrate.