Jakobsen, H. Danish Institute for Fisheries Research / Departement of Marine and Coastal Ecology, hhj@dfu.min.dk

Growth and grazing responses in two chloroplast retaining dinoflagellates: effect of light intensity and prey species
The growth and grazing responses of two phagotrophic dinoflagellates, Gymnodinium sp. and Amphidinium poecilochroum as functions of light intensity were studied. While the Gymnodinium sp. is a planktonic dinoflagellate, Amphidinium poecilochroum is a benthic dinoflagellate, which only feeds on prey associated to surfaces. Both organisms were able to retain chloroplasts from their prey (kleptochloroplast). They were both able to grow in the dark when supplied with food, but growth rates increased with light intensity. The maximum growth rate of Gymnodinium sp. was much higher than that of Amphidinium poecilochroum. However, the maximum growth rate of Amphidinium poecilochroum was reached at very low light intensities (approx. 6 mico mol phot. m^-2 s^-1), compared to Gymnodinium sp., in which the maximum growth was reached at approx. 80 mico mol phot. m^-2 s^-1. Ingestion rates were within the range reported for heterotrophic dinoflagellates, but they increase with light intensity. When cells of Gymnodinium sp., which had previously been kept in light, was subjected to complete darkness, they performed one residual cell division. Ingestion rates decreased and resumed balanced growth after some time at a lower rate. Studies of ingestion and growth rates of Gymnodinium sp. during a light:dark cycle revealed that ingestion rates were highest during the light period, while division rates were highest during the dark period. Prey selection was studied in Gymnodinium sp. Even though this species was fed a range of similar sized algae belonging to different alga classes, it only fed on cryptophyte algae
Day: Tuesday, Feb. 2
Time: 02:45 - 03:00pm
Location: Hilton of Santa Fe
Code: SS01TU0245H