THE LONG-TERM DYNAMICS OF ICHTHYOPLANKTON BIODIVERSITY IN THE OPEN PART OF THE SOUTHEASTERN BALTIC SEA

Based on long-term AtlantNIRO investigations and published data, the dynamics of Shannon's index of general diversity and Simpson's dominance index were studied in the ichthyoplankton of the open part of the southeastern Baltic Sea. Beginning from the late 1940s to 1990s, the index of general diversity exhibited a stable downward trend, whereas the dominance index permanently increased. It was caused by a drastic decline in the cod egg abundance and a significant growth of the sprat abundance. As result, a shift was observed from poly-dominance to monodominant ichthyoplankton assemblage. Mechanisms that compensate the low species saturation of the ichthyoplankton assemblage diversity are discussed.