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The importance of microzooplankton versus phytoplankton to copepod populations during late winter and early spring in Lake Michigan

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Feeding rates of the calanoid copepod Leptodiaptomus sicilis on natural assemblages of phytoplankton and microzooplankton were evaluated during late winter and early spring in Lake Michigan. Microzooplankton were the preferred food source for this copepod, and larger size fractions of phytoplankton were preferred to smaller size fractions. Ingestion rates of total chlorophyll a ranged from 2 to 14 ng·copepod–1·day–1, while ingestion rates of micro zoo plank ton biomass ranged from 0.04 to 0.15 µg C·copepod–1·day–1. In these experiments, microzooplankton carbon accounted for 22%–74% of the total carbon ingested. Clearance rates of microzooplankton carbon were positively related to the larger size fractions of chlorophyll a and to total suspended solids. Measured ingestion rates of microzooplankton and phyto plankton carbon suggest that calanoid copepod populations have the potential to control microzooplankton production in late winter and early spring, and even with an abundance of phytoplankton carbon, food availability may limit the reproduction of L. sicilis. Because microzooplankton contribute significantly to the diet of these copepods, stimulation of the microbial food web by terrigenous inputs of nutrients and carbon may be transmitted to higher trophic levels (i.e., mesozooplankton and their predators) through heterotrophic flagellates and protozoans.

Nous avons déterminé les taux d'alimentation du copépode calanoïde Leptodiaptomus sicilis sur les communautés naturelles de phytoplancton et de microzooplancton à la fin de l'hiver et au début du printemps au lac Michigan. Le microzooplancton constitue la source de nourriture préférée de ce copépode et les fractions de tailles plus grandes du phytoplancton sont choisies de préférence aux de tailles plus petites. Les taux d'ingestion de chlorophylle a varient de 2 à 14 ng·copépode–1·jour–1, alors que les taux d'ingestion de la biomasse du microzooplancton varient de 0,04 à 0,15 µg C·copépode–1·jour–1. Dans ces expériences, le carbone du microzooplancton représente de 22 à 74 % du carbone total ingéré. Les taux de clearance du carbone du microzooplancton sont en corrélation positive avec les fractions de tailles plus grandes de chlorophylle a et avec les solides totaux en suspension. Les taux d'ingestion de microzooplancton et de phytoplancton mesurés laissent croire que les populations de copépodes calanoïdes ont le potentiel de contrôler la production du microzooplancton à la fin de l'hiver et au début du printemps; même s'il y a une abondance de carbone du phytoplancton, la disponibilité de la nourriture peut restreindre la reproduction de L. silicis. Parce que le microzooplancton contribue de façon significative au régime alimentaire de ces copépodes, la stimulation du réseau alimentaire microbien par les apports de nutriments et de carbone d'origine terrestre peut se transmettre aux niveaux trophiques supérieurs (c'est-à-dire au mésozooplancton et à ses prédateurs) par l'intermédiaire des flagellés hétérotrophes et les protozoaires.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: October 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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