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Invasion of an estuarine transition zone by Dreissena polymorpha veligers had no detectable effect on zooplankton community structure

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Abstract:

Large numbers of the filter-feeding larval stage of zebra mussels (Dreissena polymorpha) (veligers) have been advected into the estuarine transition zone (ETZ) of the St. Lawrence River. In 1994, they became the dominant member of the tidal freshwater zooplankton assemblage of the ETZ (and subsequently the true estuarine assemblage) during summer months. These changes in community structure have not, however, been reflected in changes in the abundance of preinvasion taxa. Abundance of potential planktonic competitors such as rotifers and the cladoceran Bosmina longirostris fluctuated between years but did not decline following the invasion. Only densities of the copepod Eurytemora affinis declined in 2000 and 2001, but this could not be definitively associated with the invasion. Synchronous variation among different zooplankton groups suggests that environmental forcing related to or correlated with temperature anomalies is the major cause of interannual variation in the abundance of zooplankton taxa. The negative correlation between veliger abundance and salinity indicates that the ETZ acts as a sink for the larval stages of the zebra mussel. Their precise fate remains uncertain, but our study suggests that this invasion has had little or no impact on this pelagic community in spite of the numerical dominance of veligers.

Un grand nombre de larves véligères à alimentation par filtration de la moule zébrée (Dreissena polymorpha) ont été entraînées par advection dans la zone de transition estuarienne (ZTE) du fleuve Saint-Laurent. En 1994, elles sont devenues l'élément dominant des peuplements intertidaux de zooplancton de la ZTE (pour former ensuite le véritable peuplement estuarien) durant les mois d'été. Cependant, ces changements de structure de communauté n'entraînent pas de changements d'abondance des taxons présents avant l'invasion. L'abondance des compétiteurs planctoniques potentiels, tels que les rotifères et le cladocère Bosmina longirostris, fluctue d'une année à l'autre, mais il n'y a pas eu de déclin après l'invasion. Seules les densités du copépode Eurytemora affinis ont diminué en 2000 et 2001, mais le déclin ne peut être clairement associé à l'invasion. L'existence de variations synchrones parmi les différents groupes du zooplancton laisse croire que le forçage environnemental associé aux anomalies de température, ou en corrélation avec elles, est la cause principale de la variation d'abondance des taxons du zooplancton. La corrélation négative entre l'abondance des véligères et la salinité indique que la ZTE agit comme un puits pour les stades larvaires de la moule zébrée. Leur sort exact reste incertain, mais notre étude laisse croire que cette invasion a eu peu ou pas d'impact sur la communauté pélagique, malgré la dominance numérique des véligères.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2005

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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