. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 176 M. SAIGUSA AND T. AKIYAMA Time of day Tide height (m) 0 6 12 18 0 Oct. 20. Figure 9. The relationship between the daily timing of emergence and the heights, on the same day, of two low tides (LII7 and! II 2). The data on emergence are the same as in Figure 6A. To make that relationship much clearer than in Figure 6A. the numbers of emerged midges are shown as a percentage of the total number collected per day. The vertical bar shows the scale of 20%. The right panel shows the fluctuation of the heights of the
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 176 M. SAIGUSA AND T. AKIYAMA Time of day Tide height (m) 0 6 12 18 0 Oct. 20. Figure 9. The relationship between the daily timing of emergence and the heights, on the same day, of two low tides (LII7 and! II 2). The data on emergence are the same as in Figure 6A. To make that relationship much clearer than in Figure 6A. the numbers of emerged midges are shown as a percentage of the total number collected per day. The vertical bar shows the scale of 20%. The right panel shows the fluctuation of the heights of the two low tides (/JI7 and MI'.1). turbulence (Enright, 1965). Cyclical or noncyclical changes in hydrostatic pressure also cause behavioral re- sponses in amphipods (Enright, 1962; Morgan, 1965). Hydrostatic pressure fluctuations do not entrain an 'en- dogenous' rhythm, but since they coincide with the tidal cycles in the field, they could be the zeitgeber of the tidal rhythm. But, at least for the swimming activity of intertidal isopods, the 24-h day-night cycle does not seem to be a zeitgeber of tidal rhythms (Enright, 1963). In Chmio emergence rhythm, Neumann (1966, 1976) showed that the semilunar timing is entrained by the ar- tificial moonlight given in the laboratory for 3-4 nights every 30 days. According to Neumann's hypothesis (Neu- mann, 1976, 1985, 1987), daily timing of emergence is controlled by a circadian clock that is entrained by a 24- h day-night cycle only. But the phase of the tidal cycle differs according to the habitat of animals ( see Fig. 9 in Saigusa, 1988). Neumann's hypothesis cannot explain why the phase of the daily emergence rhythm coincides with the time of low tide in each larval habitat. Moreover, as indicated by this study, the phase of the daily emergence cycle was largely shifted through the year, with respect to the 24-h day-night cycle. Such a large phase-shift could be explained in terms of the tidal rhythm. In crab larval release acti
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