Effects of combined temperature and salinity on the entrainment of endogenous rhythms in the shore crabcarcinus maenas

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Abstract
Shore crabs (Carcinus maenas) were exposed in the laboratory to simultaneous, artificial tidal cycles of temperature and salinity. Cycles applied with high salinity coincident with low temperature, the normal pattern of such variables on the shore in summer, induced exogenous tidal rhythmicity at times of low salinity and re‐set endogenous circatidal rhythmicity. In subsequent constant conditions the endogenous circatidal rhythm persisted with maximum activity at “expected”; times of high salinity/low temperature. When the two variables were applied in tidal antiphase the dominant cycle of activity during treatment is an apparent tidal cycle driven by episodes of low salinity. In constant conditions after such treatment, however, a semi‐circatidal (6.2 h) pattern of activity was exhibited, suggesting that summer high tide characteristics of high salinity and low temperature applied in tidal antiphase entrain separate circatidal components of the crabs’ physiological clocks.