Littoral-pelagic interactions in shallow warm temperate lakes

GONZÁLEZ SAGRARIO, MA DE LOS ANGELES

Natal

Simposio; XIII Congresso Brasileiro de Limnologia; 2011

Shallow lakes are complex systems where pelagic and littoral organisms interact through resource exploitation, like food and habitat. Top-down control on zooplankton could be high and it has been demonstrated that submerged macrophytes offer a daytime refuge to zooplankton when avoiding pelagic fish in open waters of north european cold temperate lakes. Shallow warm temperate and tropical lakes seem to differ in their functioning and structure from cold lakes, being this contrast probably associated to their community structure. A combination of field and laboratory experiments and field surveys were performed to understand pelagic fish dependence on zooplankton and the role of aquatic plants as refuge areas. Mesocosm experiments demonstrated that zooplankton decreased in treatment having plants and a study of horizontal diel migration showed that zooplankton avoided littoral areas, particularly large size cladoceran and copepod species. In contrast, littoral areas become a refuge for a rich assemblage of macroinvertebrates and small littoral fish species. Furthermore, field and laboratory experiments reveled that littoral macroinvertebrates exerted a high predation impact on the zooplankton community, and that multiplicity of predator types caused a reduction of an 80% of the planktonic populations. Moreover, pelagic fish diets showed a high dependence on zooplankton. In conclusion, these studies showed that zooplankton is heavily preyed in open waters by pelagic fish and that submerged macrophytes are risky areas for zooplankton and could not be used as a refuge from pelagic predators. Equally important, the effectiveness of macrophytes as a refuge area is dependent on the composition of the littoral predator assemblage hosted by plant beds and constrained by the density and diversity of predators, showing a contrast in lake functioning for cold and warm shallow lakes.