Prey size spectrum and bioenergetics of the mixotrophic dinoflagellate Karlodinium armiger

Abstract

We studied the functional and numerical response and prey size spectrum in the tube-feeding dinoflagellate Karlodinium armiger. Growth rates were very low when no food was supplied (0.01 to 0.06 d-1). When K. armiger was fed the dinoflagellate Heterocapsa triquetra and the cryptophyte Rhodomonas salina, maximum growth rates (μ) were 0.48 and 0.55 d-1 and maximum ingestion rates were 215 and 597 pg C cell-1 d-1, respectively. Much lower prey concentrations were required to saturate growth rates compared to the saturation of ingestion rates. The optimal prey size, in terms of ingestion rates, was ∼13 μm, which is close to the size of the predator. Smaller prey (< 8 μm) were ingested at low rates (20 to 24 pg C cell-1 d-1), but supported fairly high growth rates (0.35 to 0.45 d-1). No upper prey size limit for ingestion was found. Maximum growth rates at food saturation depended more on prey taxa (cryptophytes) than on prey size. K. armiger's large range of prey types, wide prey size spectrum and nutritional flexibility seem to make it a significant competitor in marine plankton. © Inter-Research 2008.