Response of a zooplankton community to the addition of unsaturated fatty acids: an enclosure study

1. The effect of the addition of emulsions with different fatty acid composition to a semi-natural zooplankton community was studied in enclosures. 2. The reactions of different taxa in the zooplankton community to the addition of emulsions were different. The copepods showed almost no reaction, nor did the selective cladocerans (Bosmina) or rotifers (Synchaeta or Polyarthra). The non-selective filter-feeding cladocerans Daphnia and Ceriodaphnia, and the rotifer Keratella, showed responses to the addition of the emulsions. 3. Keratella showed the highest density in the enclosures with high amounts of highly unsaturated fatty acids added, whereas both Daphnia and Ceriodaphnia reached the highest numbers in the enclosures where we added emulsions of saturated fatty acids only. 4. Our results suggest that different taxa may be limited by different factors, even though they use similar food sources. Hence, we conclude that it is very difficult to generalize on the limiting factors in aquatic systems.