Macroalgal and cyanobacterial chemical defenses in freshwater communities

Abstract

Algae and cyanobacteria are important sources of primary production in freshwater systems and they figure prominently in estimates of carbon budgets, dissolved oxygen concentration, and nutrient recycling in those habitats (Howarth et al. 1988; Schippers et al. 2004). In recent years, these groups have garnered much negative attention as a result of their ability to dominate aquatic systems receiving chronic nutrient inputs. Freshwater blooms of these photoautotrophs have been shown to be positively influenced by an array of abiotic factors, including low N:P ratios, low light levels, high pH, and stratification of the water column (Elser 1999; Paerl et al. 2001). Nevertheless, there has been a growing understanding that biologically active secondary metabolites also play a role in mediating the persistence of these outbreaks by deterring herbivores and shifting grazing pressure toward chemically undefended species (Sterner 1989).