Abstract
Abstract. Living benthic foraminifera of Flensburg Fjord were surveyed in June 2006. The muddy and organic-rich sediments of the inner fjord were dominated by Elphidium incertum. E. incertum and E. excavatum were frequent in muds and sandy muds of the fjord loop around Holnis Peninsula and in the outer part. Gelting Bay yielded a different biofacies, indicating a brackish and sandy habitat, poor in food supply and with microfauna dominated by Ammonia beccarii and E. albiumbilicatum. The central fjord and nearshore zones of the loop were characterized by sandy muds, relatively poor in food and occupied by A. beccarii, E. incertum and E. excavatum subspecies. High abundances of E. excavatum were encountered in the innermost fjord, with fine-grained and organic-rich muddy sediments.A comparison with previous studies revealed the profound changes in species composition in the outer Flensburg Fjord since the 1970s. A decline in numbers of Ammotium cassis and flourishing of Ammonia beccarii in Gelting Bay were recognized. These changes are most likely associated with decreased intensity and frequency of salt-water inflows into the Baltic Sea since the 1960s. It is inferred that the decline of A. cassis is similar to that of Eggerelloides scaber, which currently is found only in depressions of Kiel Bight with higher salinity.
Highlights
Foraminifera in the Baltic Sea have been investigated since the nineteenth century (Schulze, 1875; Möbius, 1889; Levander, 1894)
Correlations of some species to grain-size and food particles support the idea about role of grain size and food in distribution of benthic foraminifera in the Flensburg Fjord
The inner Flensburg Fjord (Biofacies 1) was dominated by Elphidium incertum dwelling within muddy sediments rich in organic matter
Summary
Foraminifera in the Baltic Sea have been investigated since the nineteenth century (Schulze, 1875; Möbius, 1889; Levander, 1894). Studies on foraminiferal ecology in the SW Baltic Sea, initiated by Rottgardt (1952), established temperature and salinity as the most important controlling ecological factors for benthic foraminifera, whereas substrate was assumed to be of minor significance (Lutze, 1965). For the central Baltic Sea, it was shown that a northward decrease in salinity, temperature and oxygen content is reflected by reduced benthic foraminiferal diversity and abundances (Hermelin, 1987). A decrease in salinity as a background reason for the decline of Ammotium cassis across the Kiel Bight was suggested by Schönfeld & Numberger (2007a) and Nikulina et al (2008) These authors assumed that reduced salinity prevents formation of a stable halocline, which is necessary to provide a high supply of suspended food particles – essential for the feeding of A. cassis (Olsson, 1976)
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