. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 290 R. B. FORWARD ET AL. N I Coastal evening n=2l Low tide. -I Sunset .1 • 4 Other Sunset ,1 times Time (h) «4 Other times FIGURE 1. Number of crabs releasing larvae (ordinate) at times (abscissa) relative to sunset in estuary A. Crabs were under constant conditions in the laboratory and releasing was monitored during a 5-h interval on successive nights (N) when spring high tides (A) or neap low tides (B) occurred during the evening on the nearest coast. On N1 in A high tide occurred at about the time of sunset while low tid
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 290 R. B. FORWARD ET AL. N I Coastal evening n=2l Low tide. -I Sunset .1 • 4 Other Sunset ,1 times Time (h) «4 Other times FIGURE 1. Number of crabs releasing larvae (ordinate) at times (abscissa) relative to sunset in estuary A. Crabs were under constant conditions in the laboratory and releasing was monitored during a 5-h interval on successive nights (N) when spring high tides (A) or neap low tides (B) occurred during the evening on the nearest coast. On N1 in A high tide occurred at about the time of sunset while low tide occurred at this time in B. The sample size (n) on each night is shown and "other times" indicates the number of releases at times other than the sampling time. For example the releases shown on N2 for "other times" indicate those that occurred between the end of the first and beginning of the second sampling interval. The second release of a crab is indicated by an open histogram. to laboratory conditions. The slopes of the regression lines for releasing at both evening high and low tides were significantly different from zero (/-test; P < ). When the two regressions were compared by an analysis of covariance, neither the slopes nor the intercepts were significantly different (F-test). These findings suggest release time is not related to coastal tides, and the data in Figures 1 and 2 were therefore combined for the following analysis. Larval release predominantly occurred within a specific time interval on con- secutive days in constant conditions, which suggests the crabs have an endogenous rhythm. The period of the rhythm of individual crabs can be estimated from the time between consecutive larval releases. Nineteen percent of the crabs released on two consecutive nights. The mean time between releases was 24 h (SE = 15 min; n = 25), when rounded off to the nearest 15-min interval. In addition the period length of the population rhythm can b
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
