Transport of diatom frustules by copepod fecal pellets to the sediments of Lake Michigan1

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Abstract
Zooplankton fecal pellets expelled near the surface of lakes provide a mechanism for removal of diatoms to deeper water. Scanning electron micrographs show that copepod fecal pellets, collected from Lake Michigan, contained fractured specimens of 21 species of diatoms. Few intact diatoms were observed and many frustules were reduced to small fragments during ingestion by the copepods. The peritrophic membrane surrounding the pellets is composed of polysaccharides, one of which is chitin. This membrane is broken down by bacterial decomposition in 6–14 days as the pellets settle at an average velocity of 4.7 m d−1. As a result, pellets released near the surface in water more than 70 m deep do not transport diatom fragments directly to the sediment. In a large proportion of Lake Michigan the transport of diatoms to the sediments via pellets originating near the surface is unlikely, since about 60% of the lake is >70 m deep.

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