Zooplankton of 15 lakes in the Southern Central Alps: comparison of recent and past (pre-ca 1850 AD) communities

We report the results of a study on modern zooplankton community as well as on Cladocera sub-fossil remains from 15 high altitude lakes in the Italian Central-Southern Alps, aimed at investigating changes after 19th Century industrialisation. Present-day communities were compared to those of the pre-industrial period (approximately pre-1850 AD). Numerical analysis suggests a relationship between environmental variables, such as pH or total phosphorus, and the cladoceran community structure. However, as found in previous studies, another important environmental variable not included in numerical analysis, is presence or absence of fish. Arctodiaptomus alpinus was not found at pH levels lower than 6.21, while Daphnia lacked from lakes where fish were regularly introduced. Daphnia re-colonised the today fish-less Lago Paione Inferiore, whereas in the past, with a regular introduction of fish, only rotifers and a few Cyclops were found. The re-colonisation is interpreted by regarding the three Paione lakes as parts of a cascade system, where a transport from the upper Lago Paione Superiore to the lower Lago Paione Inferiore can take place, and the sediments represent a kind of an "egg bank".