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Marine Ecology Progress Series

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MEPS 441:65-78 (2011)  -  DOI:

Feeding on copepod fecal pellets: a new trophic role of dinoflagellates as detritivores

Louise K. Poulsen1,*, Morten Moldrup2, Terje Berge3, Per Juel Hansen2

1Technical University of Denmark, Charlottenlund Castle, Jægersborg Allé 1, 2920 Charlottenlund, Denmark
2Marine Biological Section, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark
3Marine Biological Section, University of Copenhagen, Østre Farimagsgade 2D, 1353 Copenhagen K, Denmark

ABSTRACT: Recent field studies indicate that dinoflagellates are key degraders of copepod fecal pellets. This study is the first to publish direct evidence of pellet grazing by dinoflagellates. Feeding and growth on copepod fecal pellets were studied for both heterotrophic (4 species) and mixotrophic dinoflagellates (3 species) using a combination of classic incubation experiments and video recordings of feeding behavior. Fecal pellets were produced by adult Acartia tonsa feeding on Rhodomonas salina. Two mixotrophic species (Karlodinium armiger, a gymnodinoid dinoflagellate, Gy1) and all heterotrophic dinoflagellates (Gyrodinium dominans, Gyrodinium spirale, Diplopsalis lenticula, Protoperidinium depressum) studied fed on fecal pellets. Using natural concentrations of dinoflagellates and copepod fecal pellets, average ingestion rates of 0.2 and 0.1 pellets cell−1 d−1 and clearance rates of between 0.2 and 0.3 ml cell−1 d−1 were obtained for G. spirale and P. depressum, respectively. Pellet feeding resulted in average growth rates of 0.69 and 0.08 d−1 with growth yields of 0.58 and 0.50 for G. spirale and P. depressum. Important factors for the grazing impact of the dinoflagellates on fecal pellets in this study were: dinoflagellate concentration, the dinoflagellate-to-pellet size ratio, the feeding mechanism, pellet food source, and pellet age. This study reveals a new trophic role for dinoflagellates as detritivores, and shows that large (>20 µm) heterotrophic dinoflagellates alone can account for reported pellet degradation rates in field studies. Thus, dinoflagellates can function as an effective ‘protozoan filter’ for fecal pellets in the water column.

KEY WORDS: Detritivorous feeding · Fecal pellet degradation · Fecal pellet grazing · Detection distance · Microzooplankton · Chemosensory response · Avoidance

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Cite this article as: Poulsen LK, Moldrup M, Berge T, Hansen PJ (2011) Feeding on copepod fecal pellets: a new trophic role of dinoflagellates as detritivores. Mar Ecol Prog Ser 441:65-78.

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