Long-term dynamics of zooplankton in the Matiţa and Merhei shallow lakes (the Danube Delta, Romania). 1. Diversity and abundance

Abstract

Long-term dynamics of zooplankton in the Matiţa and Merhei shallow lakes (the Danube Delta, Romania). 1. Diversity and abundance The present paper presents significant changes occurred in the multi-annual dynamics of zooplankton diversity and abundance (1980-2007), under the pressure of human-induced eutrophication in two shallow lakes specific for the Danube Delta. Zooplankton community from lakes Matiţa and Merhei was characterized by high species richness but low abundance values until 1981, in ecological conditions unaffected by eutrophication. For the next ten years, due to obvious increases of human pressures, zooplankton species richness decreased with 52% and 63%, respectively, while abundance values increased with 39% and 16%, respectively. After 1991, the social and economic changes in the Danube countries from the Central Europe led to nutrient input decreases. As a result, lake ecosystems from the Danube Delta showed lower trophicity values and their ecological parameters tended to recover. Analyses on the dynamics of the Shannon-Wiener's informational entropy index, Pielou's evenness and Simpson's index of dominance offered additional information and reduced the heterogeneity of the data regarding the species richness and the numerical abundance dynamics. Moreover, correlation analyses suggested the influences of human-induced changes of nutrient inputs on the multi-annual zooplankton dynamics.