Interactions multispécifiques: répartition spatio-temporelle des larves de capelan (Mallotus villosus), d'éperlan (Osmerus mordax) et de hareng de l'Atlantique (Clupea harengus harengus) an sein de la communauté planctonique de l'estuaire moyen du Saint-Laurent

Abstract

The study of the spatial and temporal organization of the planktonic community of the middle estuary of the Saint Lawrence River revealed that fish larvae were distributed in such a way as to minimize interactions between species. Smelt (Osmerus mordax) larvae were distributed upstream whereas capelin (Mallotus villosus) and Atlantic herring (Clupea harengus harengus) larvae were found downstream in June 1979. Capelin larvae were more abundant at the surface (0–20 m) whereas herring larvae were concentrated in deeper waters (20–60 m). The ecological separation observed was maintained by multiple physical factors and appeared to be the consequence of species-specific reproductive strategies. The abundance of chaetognaths, euphausiids, and amphipods in deeper waters suggests that these forms could be important predators of fish larvae. Herring larvae may be particularly vulnerable because of their distribution in deep water. Capelin larvae which are very abundant in June could also be vulnerable to predation during the diurnal migrations of the macroplankton. Smelt larvae appear to be little affected by predation from these forms as a result of their distribution in fresher waters.