Basic and Applied Ecology 11 (2010) 432–439 Effect of macrophyte community composition and nutrient enrichment on plant biomass and algal blooms E.S. Bakker a,∗ , E. Van Donk a,b , S.A.J. Declerck a,c , N.R. Helmsing a , B. Hidding a , B.A. Nolet d a Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Rijksstraatweg 6, 3631 AC Nieuwersluis, The Netherlands b Institute of Environmental Biology, Palaeoecology, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands c Laboratory of Aquatic Ecology and Evolutionary Biology, K.U. Leuven, Ch. De Beriotstraat 32, B-3000 Leuven, Belgium d Department of Animal Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Rijksstraatweg 6, 3631 AC Nieuwersluis, The Netherlands Received 2 November 2009; received in revised form 18 May 2010; accepted 19 June 2010 Abstract Submerged freshwater macrophytes decline with increasing eutrophication. This has consequences for ecosystem processes in shallow lakes and ponds as macrophytes can reduce algal blooms under eutrophic conditions. We hypothesize that the productivity of submerged vegetation, biomass change under eutrophication and the suppression of algal blooms may be affected by macrophyte community composition. To test our hypothesis, we established three macrophyte community types in 36 fishless experimental ponds: one dominated by the oligotrophic species Chara globularis, one dominated by the eutrophic species Potamogeton pectinatus and a diverse vegetation which became co-dominated by Elodea nuttallii and C. globularis, and we fertilized half of the ponds. The macrophyte communities produced different amounts of biomass and they responded differently to fertilization. The community dominated by Potamogeton produced the lowest overall biomass, but was not affected by nutrient addition. The communities dominated by Chara and co-dominated by Elodea and Chara produced more than four-fold the amount of biomass produced in Potamogeton communities under oligotrophic conditions, but were strongly negatively affected by nutrient addition. Phytoplankton abundance did not differ significantly among the plant community types, but showed large variation within community types. There was a significant negative relationship between spring macrophyte biomass and the probability of summer algal blooms. The occurrence of algal blooms coincided with low daphnid densities and high pH (>10). We conclude that the macrophyte community composition, characterized by the dominant species, strongly affected the amount of biomass production as well as the short-term response of the vegetation to nutrient enrichment. Macrophyte community composition had no direct effect on algal blooms, but can affect the occurrence of algal blooms indirectly as these occurred only in ponds with low (<100 g/m 2 DW) spring macrophyte biomass. Zusammenfassung Mit zunehmender Eutrophierung verschwinden die submersen Süßwassermakrophyten. Dies hat in flachen Seen und Teichen Konsequenzen für die Ökosystemprozesse, da Makrophyten die Algenblüten unter eutrophen Bedingungen reduzieren können. Wir stellen die Hypothese auf, dass die Produktivität der submersen Vegetation, die Veränderung der Biomasse bei Eutrophierung und die Unterdrückung von Algenblüten von der Zusammensetzung der Makrophyten-Gesellschaft beeinflusst wird. Um unsere Hypothese zu prüfen, etablierten wir drei Typen von Makrophyten-Gesellschaften in 36 fischfreien experimentellen Teichen: ∗ Corresponding author. Tel.: +31 294 239 357; fax: +31 294 232224. E-mail address: l.bakker@nioo.knaw.nl (E.S. Bakker). 1439-1791/$ – see front matter © 2010 Gesellschaft für Ökologie. Published by Elsevier GmbH. All rights reserved. doi:10.1016/j.baae.2010.06.005