Stéphane Masson

Périodicité d’alimentation du polychète Nereis diversicolor (O.F. Müller) selon les changements de la marée

Abstract:The feeding rhythm of the polychaete Nereis diversicolor (O.F. Muller) was studied during tidal cycles (spring and neap tide) at three sites in baie du Mont St-Michel and the Rance estuary in summer 1990. For most of the sites, the polychaetes were mainly feeding during spring tides when immersion occurred. Dietary activity decreased at emersion sites depending on low tide duration. During this period, the physical and chemical conditions in the mud flat sediments are not favourable to polychaetes’ activities (high temperature, high desiccation, low oxygen content) and can cause mortality or migration of the population. Repletion indices from polychaetes of the Hirel sector (baie du Mont-St-Michel) showed a decrease of their dietary’s activity during the neap tide period even if the site was permanently immersed.

Relating macroinvertebrate community structure to environmental characteristics and sediment contamination at the scale of the St. Lawrence River

There is still no assessment of the impact of sediment chemicals and environmental conditions on macroinvertebrates at the scale of the St. Lawrence River. In order to assess these impacts in the fluvial section of the St. Lawrence River including the Montreal harbour, the community structure of macroinvertebrates using different taxonomic aggregations (genus and family) and taxa attributes (abundance, presence–absence, indicator taxa) was assessed. The goal of the study was to determine the indicator taxa of macroinvertebrates along the fluvial continuum and relate changes in macroinvertebrate community to sediment chemical conditions and environmental characteristics of habitats using variance partitioning. This study also evaluated which taxonomic level and taxa attributes of macroinvertebrates were the most suitable for bioassessment of quality of sediments and habitat environment in the St. Lawrence River. Four different macroinvertebrate assemblages were found distributed along the fluvial continuum using either abundance or presence–absence data and genus or family levels. Indicator taxa characteristic of the different macroinvertebrate communities were associated with the sediment contamination gradient. However, habitat environmental characteristics (water masses, sulphur and DOC in sediments) had more influence on macroinvertebrate assemblages than sediment contamination. Our study confirms that family level analysis can give information comparable to the genus level analysis using presence–absence or abundance of macroinvertebrates, yet a higher number of indicator taxa were detected at the genus level.