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Changes in spring phytoplankton communities and nutrient dynamics in the eastern basin of Lake Erie since the invasion of Dreissena spp.

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Abstract:

Distinct changes have occurred in the size and composition of the spring phytoplankton community in the eastern basin of Lake Erie following the introduction of Dreissena. Since 1996, total phytoplankton biovolume has decreased to approximately 20% of pre-Dreissena levels, whereas postinvasion concentrations of spring soluble nutrients, particularly silica, have been substantially elevated compared with earlier years. Spring dominance has shifted from a mix of pennate and large centric diatoms and pyrrophytes to three centric diatoms with high silica requirements: Aulacoseira islandica, Stephanodiscus hantzschii, and Stephanodiscus parvus, and the overall diversity and species richness of the spring phytoplankton community has declined significantly. In addition, current April silica concentrations are approximately twice as high as historical (i.e., 1960s–1980s) winter maxima, indicating that the silica content of the lake has increased since the dreissenid invasion. These results suggest that the severe silica depletion caused by increased anthropogenic inputs of nutrients during the last century has been mitigated through a decrease in diatom production, most likely brought about by dreissenid grazing.

Il s'est produit de nets changements dans la taille et la composition de la communauté printanière de phytoplancton dans le bassin oriental du lac Érié depuis l'introduction de Dreissena. Depuis 1996, le biovolume total du phytoplancton a décru jusqu'à environ 20 % des valeurs pré-Dreissena, alors que les concentrations de nutriments solubles au printemps, particulièrement de la silice, se sont accrues substantiellement après l'invasion par comparaison aux années antérieures. La dominance au printemps a changé d'un mélange de diatomées pennées et centriques de grande taille et de pyrrhophytes à une dominance de trois diatomées centriques, Aulacoseira islandica, Stephanodiscus hantzschii et Stephanodiscus parvus, à forts besoins en silice; la diversité globale et la richesse spécifique de la communauté printanière de phytoplancton ont diminué de façon significative. De plus, les concentrations actuelles de silice en avril sont approximativement deux fois plus élevées que les maximums hivernaux du passé (i.e., les années 1960–1970), ce qui montre que le contenu en silice du lac a augmenté depuis l'invasion des dreissénidés. Ces résultats indiquent que la réduction importante de silice due à l'accroissement des apports anthropiques de nutriments au cours du siècle dernier a été mitigée par un déclin de la production de diatomées très probablement causé par le broutage des dreissénidés.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: July 1, 2006

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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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