Effects of Greater flamingo Phoenicopterus ruber on macrophytes, chironomids and turbidity in natural marshes in Donana, SW Spain

Abstract

Top predators and nutrient inputs are important factors determining the structure of freshwater aquatic systems. Greater flamingos (Phoenicopterus ruber) have been shown to destroy submerged macrophytes and may promote a switch from clear water to turbid water in the temporary marshes of Donana National Park. We excluded flamingos from twenty 4x4 m plots distributed between two lucios (shallow seasonal lakes) within the marshes from February to July 2004. In July, we measured total suspended solids (TSS), macrophyte biomass and abundance and size of chironomid larvae in the twenty exclosures and twenty adjacent control plots. TSS was lower and macrophyte biomass was higher in exclosures, but not significantly so. Flamingos were found to cause a significant reduction in chironomid abundance and an increase in the proportion of larger larvae. The effect of exclusion was greater where the density of flamingos was highest. Comparison with the results of previous studies suggests that the impact of flamingos is context dependent and largely determined by bird density and/or factors related to macrophyte productivity. Water levels were especially high in 2004 owing to heavy rains, and flamingos may have stronger effects in years of lower rainfall.