The mole crab Emerita talpoida migrates with the tide in the swash zone of sand beaches. A circatidal rhythm in vertical
swimming underlies movement, in which mature male crabs show peak swimming activity 1–2 h after the time of high tides at the
collection site. In addition, there is a secondary rhythm in activity amplitude, in which crabs are maximally active following low
amplitude high tides and minimally active following high amplitude high tides. The present study determined the phase response
relationship for entrainment of the circatidal rhythm with mechanical agitation and whether the cycle in activity related to tidal
amplitude could be entrained by a cycle in the duration of mechanical agitation at the times of consecutive high tides. After
entrainment with mechanical agitation on an orbital shaker, activity of individual crabs was monitored in constant conditions with a
video system and quantified as the number of ascents from the sand each 0.5 h. Mechanical agitation at the times of high tide, midebb
and low tide reset the timing of the circatidal rhythm according to the timing relationship to high tide. However, mechanical
agitation during flood tide had no entrainment effect. In addition, a cycle in duration of mechanical agitation entrained the rhythm
in activity amplitude associated with tidal amplitude. Both rhythms and entrainment effectiveness over the tidal cycle may function
to reduce the likelihood of stranding above the swash zone.
© 2006 Elsevier B.V. All rights reserved.
The mole crab Emerita talpoida migrates with the tide in the swash zone of sand beaches. A circatidal rhythm in verticalswimming underlies movement, in which mature male crabs show peak swimming activity 1–2 h after the time of high tides at thecollection site. In addition, there is a secondary rhythm in activity amplitude, in which crabs are maximally active following lowamplitude high tides and minimally active following high amplitude high tides. The present study determined the phase responserelationship for entrainment of the circatidal rhythm with mechanical agitation and whether the cycle in activity related to tidalamplitude could be entrained by a cycle in the duration of mechanical agitation at the times of consecutive high tides. Afterentrainment with mechanical agitation on an orbital shaker, activity of individual crabs was monitored in constant conditions with avideo system and quantified as the number of ascents from the sand each 0.5 h. Mechanical agitation at the times of high tide, midebband low tide reset the timing of the circatidal rhythm according to the timing relationship to high tide. However, mechanicalagitation during flood tide had no entrainment effect. In addition, a cycle in duration of mechanical agitation entrained the rhythmin activity amplitude associated with tidal amplitude. Both rhythms and entrainment effectiveness over the tidal cycle may functionto reduce the likelihood of stranding above the swash zone.
© 2006 Elsevier B.V. All rights reserved.
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