RELATION BETWEEN POSITION OF BURROWS AND TIDAL RHYTHM OF UCA

Publisher Website
Google Scholar
Abstract
The tidal and semilunar rhythms of color change of Uca pugilator were analyzed. The phases of these rhythms appeared to be set according to the time the burrows of the crabs began to be uncovered by the receding water following a high tide and not the time of actual low tide on the beach. The amplitude of the daily pigmentary dispersion was also influenced by the time when the burrows were covered and uncovered each day. Crabs in burrows close to the high tide mark experienced a longer photoperiod daily and consequently exhibited a greater daily amplitude of pigment dispersion. A two-day phase difference, equivalent to 1.6 hours in a tidal cycle, was found between 2 groups of crabs collected from 2 discrete sets of burrows different distances from the high tide mark. The maximal pigment dispersion due to the tidal rhythm for any given hour of the day occurred 2 days earlier in the crabs collected closer to the low tide mark. Measurements of the beach where the crabs were collected revealed that the receding water began to uncover the burrows closer to the high tide mark 1.6 hours earlier than the burrows closer to the low tide mark. The daily patterns of pigment dispersion were different during the first 2 weeks of observation from patterns observed previously. Maxima of pigment dispersion did not occur in the late afternoon but were restricted to the morning hours. The absence of peaks in the afternoon resulted in cycles with a 7.4-day frequency. An 11.5-day cycle also appeared and was followed by a typical 14.8-day cycle accompanied by maxima of the daily curves in the late afternoon.