Nejstgaard, J. C.. University of Bergen, jens.nejstgaard@ifm.uib.no
Egge, J. C.. University of Bergen, jorun.egge@ifm.uib.no
Bamstedt, U. University of Bergen, ulf.baamstedt@ifm.uib.no

 
SEAWATER ENCLOSURE STUDIES ON THE NORWEGIAN WEST COAST DURING THE LAST DECADE: II. ZOOPLANKTON FOOD SELECTION AND PRODUCTION IN NATURAL PLANKTON DOMINATED BY FLAGELLATES OR DIATOMS.
 
We summarize results on zooplankton selective feeding, reproduction and development from seven one-month mesocosm experiments conducted on the Norwegian West coast between 1992 and 1998. 11-28 cubic meters of natural seawater was enclosed in translucent polyethylene bags suspended in situ. The mesocosms were treated with different combinations of nutrient additions, mesozooplankton concentrations and turbulence levels. Micro and mesozooplankton development was monitored in all mesocosms. Selective grazing rates by the microzooplankton community and copepods (Calanus) was assessed by a combination of bottle incubation techniques analysed by microscopy (Nejstgaard et al. 1997, MEPS 147:197-217). Diatom blooms generally showed higher algal biomass, primary production and copepod ingestion rates compared to flagellate blooms. However, Calanus did not select diatoms, and both the copepod reproduction and total mesozooplankton production was similar or less in the diatom blooms. This indicates a major difference in food quality between these complex natural plankton communities, and amplifies results from laboratory experiments suggesting that copepod reproductive success may be reduced during diatom blooms. However, previous laboratory experiments may have underrated the reproductive potential during natural flagellate blooms. Thus mesocosm studies may successfully be used to test laboratory derived hypotheses in a more natural and complex, but yet relatively controlled environment.
 
Day: Thursday, Feb. 4
Time: 09:45 - 10:00am
Location: Eldorado Hotel
 
Code: SS51TH0945E