Havskum, H. VKI, hha@vki.dk
Thingstad, F. University of Bergen, frede.thingstad@im.uib.no
Scharek, R. Institute of Marine Sciences (CSIC), rscharek@icm.csic.es
Peters, F. Institute of Marine Sciences (CSIC), cesc@icm.csic.es
Alcaraz, M. Institute of Marine Sciences (CSIC), miquel@icm.csic.es
Schluter, L. VKI, lsc@vki.dk
Dolan, J. Station Zoologique (URA-CNRS 716), dolan@ccrv.obs-vlfr.fr

 
ENRICHMENTS WITH PHYTOPLANKTON NUTRIENTS CAN LEAD TO A REPLACEMENT OF ALGAE BY BACTERIA
 
Organic and inorganic nutrient enrichments have been performed in 3000 L seawater enclosures in the Isefjord, Denmark, during 11 days in June 1998. Central for the experimental set-up were two sets of four enclosures, each set forming a gradient of increasing glucose addition. All enclosures received the same daily addition of phytoplankton nutrients (phosphate and nitrate), and one set was kept in excess with respect to silicate. In the enclosures where no silicate was added, enrichment with phytoplankton nutrients and glucose led to a replacement of diatoms not by other algae, but by bacteria, mainly bacteria > 2 um. When silicate became depleted, the diatom biomass decreased, and bacterial biomass and production subsequently increased. When silicate was available, diatoms were able to compete with bacteria for the uptake of mineral nutrients. Even in the silicate enclosures that were enriched with high amounts of glucose, primary production increased, while bacterial production remained constant. The size and shape of different algal and bacterial groups in relation to nutrient uptake and grazing resistance are discussed.
 
Day: Wednesday, Feb. 3
Time: 11:30 - 11:45am
Location: Hilton of Santa Fe
 
Code: SS38WE1130H