Implications for shallow lake manipulation: Results of aquaria and enclosure experiments manipulating macrophytes, zooplankton and fish

Abstract

The Massaciuccoli Lake, a 700 ha shallow lake, located in the Migliarino San Rossore Massaciuccoli Natural Park, along the Tuscan coast (Italy), has undergone a dramatic reduction of the macroalgal and submerged macrophytic communities over the last fifty years. This reduction was both in terms of the number of species and abundance, leading in recent years to a turbid water-phytoplankton dominated state and to the disappearance of submerged macrophytes. The aim of this study was to investigate, in aquaria experiments, the minimum threshold of light, necessary for the survival of a macrophyte, Myriophyllum verticillatum L., caused by sediment resuspension. Subsequently enclosure experiments were carried out with biomanipulation techniques (such as the removal of the fish community, the inoculation of zooplankton, Daphnia magna Strauss and forced reintroduction of the macrophyte) in enclosures. The results showed that, currently, the PAR intensity at the bottom of the lake is not sufficient to allow spontaneous recovery of the submerged vegetation. The positive effect of biomanipulation, due to fish removing plankton and phytoplankton-grazing, may lead to a significant clarification of the water column in the treated enclosures, allowing radication and growth of submerged vegetation. Nevertheless, an effective recovery of Massaciuccoli Lake is not likely to be achieved until an integrated approach (ranging from the reduction of the pollutant sources to partial dredging of the sediment, because of the high nutrient levels), is performed. © 2011, ALÖKI Kft., Budapest, Hungary.