. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 446 F. I. TSUJI AND E. HILL 200-. 17 21 25 29 33 37 41 Minutes after Sunset 45 49 53 FIGURE \. Plot of the number of Odontosyllis appearing after sunset on 9 August 1982. Solid line represents the normal probability curve calculated from the observed data points. Arrow indicates the mean minutes after sunset (time of peak abundance of the worms) and standard deviation. to sunset) showed a tendency to occur progressively earlier during July, to reach a minimum in early August, and to occur progressively later thereafter, with
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 446 F. I. TSUJI AND E. HILL 200-. 17 21 25 29 33 37 41 Minutes after Sunset 45 49 53 FIGURE \. Plot of the number of Odontosyllis appearing after sunset on 9 August 1982. Solid line represents the normal probability curve calculated from the observed data points. Arrow indicates the mean minutes after sunset (time of peak abundance of the worms) and standard deviation. to sunset) showed a tendency to occur progressively earlier during July, to reach a minimum in early August, and to occur progressively later thereafter, with a total seasonal range of about 30 min (Fig. 2). The days were becoming shorter (, sunset occurred earlier) throughout this interval. The length of twilight (~24 to 28 min), the time the full moon was in the sky (~ to hour), and weather conditions— even strong wind and overcast sky—had no apparent effect on the daily or fortnightly timing of spawning swarms. The first sighting of Odontosyllis was made on 13 May (last quarter moon, 15 May) when 26 worms were counted. On 15 May, many more worms were seen, but not counted. Subsequently, worms were observed on 27 May (not counted; first quarter moon, 29 May) and on 16 June (30 counted; last quarter moon, 14 June). Thereafter, regular counts were taken. Figure 3 shows a plot of number of Odon- tosyllis observed, high and low water predictions for the tide, surface water tem- perature, and phases of the moon against dates of observation. The observations representing each fortnightly peak show a reasonably good fit with a calculated normal probability curve. The results show that swarming by Odontosyllis follows a semi-lunar cyclic pattern, with peak spawning coinciding approximately with the time of minimum variation in tidal amplitude, as well as with the first and last quarter phases of the moon. The cumulative difference between the days of peak swarming and the corresponding days of the quarter moon over the int
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
