. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. July 24 24 July 25 l2 24 July 26 24 B. 20 July 30 24 04 08 12 16 July 31 2O TIME 24 O4 08 Aug I 20 24 FIGURE 1. Rhythm in swimming speeds (ordinate) over time (abscissa) for larvae col- lected on July 24 (A) and July 30, 1979 (B). Mean speeds and standard error of 45 deter- minations are shown. L is time of low tide, and H shows high tide. intensities was measured. Each group of larvae was tested at two different intensities. Larvae were then maintained in the environmental chamber until about 45 min before the next high tid
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. July 24 24 July 25 l2 24 July 26 24 B. 20 July 30 24 04 08 12 16 July 31 2O TIME 24 O4 08 Aug I 20 24 FIGURE 1. Rhythm in swimming speeds (ordinate) over time (abscissa) for larvae col- lected on July 24 (A) and July 30, 1979 (B). Mean speeds and standard error of 45 deter- minations are shown. L is time of low tide, and H shows high tide. intensities was measured. Each group of larvae was tested at two different intensities. Larvae were then maintained in the environmental chamber until about 45 min before the next high tide, when photoresponsiveness was again tested. Tidal times were established by adjusting the NO A A tide table times for Fivers Island, North Carolina, to a predicted time at the collecting site in the Newport River estuary (+ hr). The second experimental series involved determining the rhythm in phototaxis. Larvae were collected on two occasions (August 6 and 15, 1979). Tidal times advanced about 8 hr between the two runs. Larvae were sorted into three groups of about 30 individuals each and placed under constant conditions. At 2-hr inter- vals, phototaxis by larvae in each bowl was tested using the described procedure. After phototactic responsiveness was tested, the larvae were placed in new water from the collection site and fed A. salina nauplii. RESULTS Rhythm in swimming speeds The larvae have a clear endogenous tidal rhythm in swimming speeds (Fig. 1). In both trials (Fig. 1A, B) using the Fisher periodogram test (Fuller, 1976) the frequency nearest the tidal cycle is significant (P < ). The speeds increase to a maximum within 3 hr after low tide, and then decrease to a minimum about 2 hr after high tide. This pattern is seen on both test dates and is related to tidal times. This is indicated by the fact that both the time of tides and of rhythmic swimming advance by 4 hr from trial 1 (Fig. 1A) to trial 2 (Fig. IB). Speeds vary between similar maximum and minim
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
