Rhythmic functions are disturbed by environmental changes

Virtually all physiological functions show circadian and seasonal rhythms, with light (day and night, long daylength in summer and short light period in winter) as the major synchronising factor. Light-temperature interactions have been used as reliable indicators by animals for timing of reproduction, winter sleep or hibernation, changes of protective colouring and so on. The temperature increase associated with climate change has made light rhythm unreliable predictor of suitable time to carry out the function that has evolved to use the light rhythm as a reliable cue. As an example, short daylength has indicated to hares that it is time to change to white winter colouring. Since the temperature has increased so that there is no snow in latitudes, which earlier had it, the light cue results in white hares in dark background. Foxes certainly like easy hunting. There are various temperature-dependent responses of fish, which are signalled by light rhythm. Because of light-temperature interactions have rapidly changed, it is, for example, possible that hatching of fish takes place at a time that the larvae have no food after the yolk sac has been used up. In addition to the increase of temperature the oceans are suffering from decreased oxygen level (hypoxia). Hypoxia disturbs the generation of rhythms. Also, several environmental pollutants found in the aquatic environment affect rhythms. Consequently, temperature changes, hypoxia, and environmental contaminants affect aquatic life by affecting rhythmic functions. Because of this and because of interactions between temperature, hypoxia and contaminants, effects on sea life can occur after much smaller changes of any of the environmental conditions than hitherto supposed.