Possible drivers of abundance fluctuations of Chinese mitten crabs in the Elbe River and the adjacent coastal North Sea region. The top of the panel shows the abundance fluctuations for the Chinese mitten crab in the Elbe River (see Fig. 1). A–C: temporal changes in environmental variables that have been linked to Chinese mitten crab abundance. A: Mean annual riverine water quality, approximated by oxygen concentration in the Elbe River near the city of Magdeburg; B: Mean annual SST for the North Sea close to the mouth of the Elbe River; C: Annual riverine water discharge; D–F: results of logistic regressions. The predictive values (line) are drawn for all significant explanatory variables; D: oxygen content; E: SST; F: riverine water discharge. Abbreviations: SST = sea surface temperature.