Fig. 4. Valve movements of the eight specimens (M1-M8) in Koblenz during 11-17 February 1999, recorded by the Mosselmonitor®. Water temperature varied between 3.1°C and 4.3°C. Continuous recordings of individual magnitudes of shell gape, in arbitrary units. For each trace, closed is the baseline level. Dotted lines mark the change of date (0:00 h).