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Marine Ecology Progress Series

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MEPS 314:295-307 (2006)  -  doi:10.3354/meps314295

Cestode parasitism as a regulator of early life-history survival in an estuarine population of rainbow smelt Osmerus mordax

Jean-François Bourque1, Julian J. Dodson1,*, Daniel A. J. Ryan2, David J. Marcogliese3

1Département de biologie, Université Laval, Pavillon Vachon, Quebec, Quebec G1K 7P4, Canada
2Department of Mathematics and Statistics, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada
3St. Lawrence Centre, Environment Canada, 105 McGill, 7th floor, Montreal, Quebec H2Y 2E7, Canada
*Corresponding auhor. Email:

ABSTRACT: In the St. Lawrence middle estuary, the larvae and juveniles of rainbow smelt Osmerus mordax are infected with intestinal parasites (the cestode Proteocephalus tetrastomus). Such parasitism is suspected to impair growth rate, which may in turn influence the ability of smelt to migrate vertically and to be retained in the estuarine turbidity maximum (ETM), the nursery area of this population. We hypothesised that parasitism contributes to size-selective mortality by altering patterns of vertical migration, thus contributing to transport losses from the nursery area. Parasitism was found to affect growth rate, as determined by otolith microstructure analysis, and to contribute to mortality. Larvae which survived the parasitic infection were found to be, on average, larger than the uninfected survivors at some point in their early life history prior to infection. Significant size-selective mortality was observed among infected larvae relative to uninfected larvae. There was, however, no significant difference in the vertical distribution of parasitised versus non-parasitised larvae, indicating that size-selective mortality was not due to transport losses from the nursery area. Rather, starvation or predation was most likely responsible for observed mortality patterns. We illustrate that variability in the incidence of parasitic infection among years may form the basis for variability in recruitment and the abundance of the adult smelt population.

KEY WORDS: Parasite · Recruitment · Smelt · Otolith · Larvae · Size-selective mortality · Body size · Cestodes · Estuarine turbidity maximum

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