1. The response of major food-web constituents to combinations of nutrient addition and zooplanktivorous fish abundance was tested during two subsequent years in the shallow charophyte-dominated lake Naardermeer in the Netherlands, using in situ enclosures. 2. Treatment effects differed sharply between study years. In 1998, when the summer temperature was low (1721 °C), high algal biomass only developed at high nutrient levels in the presence of fish, but with no major effect on Chara biomass. In 1999, when the summer temperature was relatively high (2025 °C), algal blooms occurred at high nutrient levels regardless of fish abundance, and were associated with a drastic decline in Chara biomass. 3. Differences between years in temperature and initial zooplankton composition and biomass were likely to contribute to the varying relative importance of top-down and bottom-up effects in these enclosure experiments. 4. The results suggest that when nutrient loads are increased towards levels where the macrophyte-dominated state is being destabilised, a 'switch' is more likely to occur in warm summers. [KEYWORDS: enclosures ; multiple stable states ; shallow lakes ; submerged macrophytes ; turbidity]
Original languageEnglish
JournalFreshwater Biology
Journal publication date2004

ID: 128243