Activity patterns in Thalamita crenata Portunidae, decapoda): A shaping by the tidal cycles

The activity rhythms of the swimming Portunid Thalamita crenata have been studied on the basis of crab sightings in surveys along three transects of a mangrove swamp in Kenya. Activity is well matched to the environmental regime and is prevalent during the high tides. However, activity does not occur over the whole of the high tide, but is confined to “temporal windows”; corresponding to a water level between 10 and 30 cm. Our findings suggest that activity in Thalamita crenata is shaped by the tidal cycles and we propose that variation in hydrostatic pressure as the tide changes is the cue which elicits activity.

Key words:

• Tidal rhythms
• activity rhythms
• intertidal habitat
• mangrove swamp