Palaeoecology of Late Glacial and Holocene profundal Ostracoda of pre-Alpine lake Mondsee (Austria) — A base for further (palaeo-)biological research

Abstract

Succession of profundal ostracod palaeoassemblages in response to environmental changes during the Late Glacial and Holocene was studied in a~15-m-long sediment sequence from pre-Alpine lake Mondsee (Austria). First local ostracod assemblage zone LOAZ-1 (prior to 15,700 a BP), with low abundances of Leucocythere mirabilis and Limnocytherina sanctipatricii followed by Cytherissa lacustris, corresponds to the Pleniglacial phase of clastic-detrital sedimentation at relatively high rates. Most of the key species of LOAZ-2 (15,590 to 13,940 a BP, including the Pleniglacial–Late Glacial transition), i.e. limnocytherids, Fabaeformiscandona cf. harmsworthi, F. tricicatricosa, C. lacustris and Candona candida, reveal the significant association with high Al contents and low sedimentation rates and are classified as preferring low-productivity conditions. In contrast, Candona neglecta, dominant in LOAZ-3 (13,820 to 9960 a BP, palynologically defined as Bölling–Early Holocene) and in the last LOAZ-4 (9780 a BP to present) as well as Cypria ophtalmica (second key species in LOAZ-4) show relationship with higher productivity, elevated sedimentation rates and decreasing Al contents.Furthermore, valve biodegradation and shape disparity at different time periods and in relation to sedimentation rate changes were investigated in A-3 juveniles of Candona neglecta. The highest percentage of valves biodegraded by Actinobacteria was recorded during the Allerød, Younger Dryas and Early Holocene, when the lowest sedimentation rates occurred, whereas significantly lower frequencies of biodegraded valves were recorded during the mid-Holocene and Late Holocene, when sediment accumulation was much higher. It is also hypothesised that the degree of the valve shape variation was related to the lake productivity. During the Allerød, Younger Dryas and Early Holocene a valve shape variation significantly lower than that recorded during Late Holocene intervals, characterised by intensified lake productivity, was observed. Additionally, an agenda of potential questions and approaches that should be considered and form the core of further (palaeo-)biological research projects is offered.