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Mussel colonization is assumed to result from factors affecting recruitment and post-recruitment survival. Despite evidence of passive migration and habitat engineering by adult mussels, the contribution to population dynamics of these processes remains unknown. This research attempts to elucidate the relative importance and scale of (1) adult movement vs. recruitment and (2) of local habitat engineering vs. habitat heterogeneity, for colonization by the blue mussel, Mytilus spp., in the St. Lawrence Estuary, Quebec. Transplants of marked mussels were used to test these ideas. Our results support the hypothesis that colonization mostly occurs through disturbance-mediated adult movement. The scale of this displacement was quantified. Colonization was accelerated by topographic heterogeneity and engineered habitat propagation. These results counter the notion that mussel population dynamics are solely regulated by recruitment and growth, and suggest that distribution patterns are also upheld by adult aggregation and movement from the local scale to landscape level.

Recently, the assumption that marine populations are demographically open due to long-distance larval dispersal has increasingly been challenged. Here we present a large-scale, multi-year survey of blue mussel ( Mytilus spp.) abundance and recruitment along the Southern shore of the St. Lawrence Estuary, Quebec. Using spatial statistical tools we detected significant positive cross-covariance between upstream adults and downstream recruitment at a 14-35 km scale. Adult abundances in subsequent surveys proved to be best explained by past patterns of recruitment, rather than growth indices, or the local supply of recruits. Fucus spp., large macroalgae with much shorter planktonic periods, displayed no evidence of dynamic coupling. Recruitment was instead correlated with growth rate, indicating that local conditions may drive rates of reproduction by Fucus spp. plants. These results provide the first direct quantification of spatio-temporal demographic coupling between adult production and recruitment using survey data, with consequences for metapopulation and marine reserve design.

A prevalence of 76% and a mean intensity of 42.7 Anisakis simplex was found in harbour porpoises (Phocoena phocoena) (N = 78) by-caught in cod gill nets set by fishers from the Gaspe area in summer 1993. No young-of-the-year porpoises (N = 12) were infected. Prevalence and mean intensity among immature and adult porpoises as well as between sexes and length-classes were not significantly different. Anisakis simplex was present in the three stomach compartments of harbour porpoises. Adult stages were proportionately less abundant in the main and pyloric stomachs than the forestomach. Percent intensity of A. simplex was influenced by maturity of harbour porpoises. Gravid female A. simplex contained up to 818,000 eggs. Egg number was highly correlated with worm uttering volume. Density effects were not demonstrated, possibly due to high variability of egg number, total length, uterine and total worm volume between parasites from each stomach and between stomachs of harbour porpoise.

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