In the littoral zone of the St-Lawrence River (Quebec, Canada), benthic and phytophilous macroinvertebrates were studied in order to find and to explain relationships between structure of these animal communities and abiotic (substrate, water depth, current velocity) or biotic (marophytes species) factors . Benthos was sampled at 16 sites in spring, when there was no macrophytic vegetation, and in summer . Phytomacrofauna was sampled at 30 sites in summer . The data were analyzed using simple and partial correlations, stepwise regression, reciprocal averaging and canonical correlation analysis .

The population dynamics of Pisidium amnicum have been studied in one population of the St. Lawrence River over a 2-year period during which 19 samples were taken. The species can live up to 3 years and it is iteroparous; individuals generally attain sexual maturity after 1 year and they reproduce twice, once at 2 and once at 3 years of age. In adults, mortality is lower in winter than during the rest of the year and mortality rates are twice as high during the 1st year than during the 2nd year. Total dry weight (PT, in milligrams) is related to maximum length (L, in millimetres) according to the equation PT = 0.0283∙L3,80 and flesh dry weight (PC, in milligrams) is related to length as follows: PC = 0.007∙L3,18. The annual production to mean biomass (P/B) ratio is 1.4, the mean annual production being 1.298 mg/m2 of total dry weight and 107 mg/m2 of flesh weight. Comparing these results with those obtained for the gastropod Bithynia tentaculata in the same environment and at the same period of the year has shown that the growth of Pisidium amnicum is far less influenced by the temperature regime than that of the other species and that its production is at least 10 times lower.

The life cycle of a population of Sphaerium striatinum in the St. Lawrence River (Québec) was studied over a 13-month period. This species has a life-span of 2–3 years and is iteroparous; individuals start producing young at the age of 1 year. Growth in length reached a maximum of 0.010 mm/day between the ages of 0 and 8 months, while the maximum increase in weight occurred during the 2nd year, representing 46% of the total growth. The mean population density was 737 individuals/m2 for the months of May to November 1979; the mean biomass values were 20.6 and 2.1 g/m2, respectively, for total dry weight and dry weight minus shells. Young of the year and yearlings combined represent 96% of the total production, which was calculated to be 14.9 g (total dry weight)/m2. The production to biomass ratio (P/B) decreased with the age of a generation and was 0.72 for the entire population. A comparison of our results with those in the literature indicates that individual growth rates are slower in the St. Lawrence population and that larvae, adults, and reproductive individuals are smaller in size; however, the population's life expectancy is greater. This longer life-span and smaller individual size, along with a delayed sexual maturity, can be explained by the environmental temperature regime.[Journal translation]