The effect of light and darkness on hatching in the pomacentrid Abudefduf saxatilis |
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Authors: | Florence A McAlary William N McFarland |
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Institution: | (1) Wrigley Marine Science Center, Hancock Institute of Marine Studies, University of Southern California, P.O. Box 398, Avalon, CA, 90704, U.S.A. |
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Abstract: | Synopsis Reports that pomacentrid embryos hatch after dusk are confirmed by photic manipulation of sergeant major eggs. Embryos placed
in the dark for 20 minutes or longer prior to their normal hatching after sunset hatched, whereas controls held in light did
not hatch. Percent of hatched embryos correlated with increasing exposure to darkness up to one hour after which no further
improvement in hatching was observed. Embryos maintained in continuous light during their normal twilight hatching period
did not hatch. Also, embryos exposed to 60 minutes of darkness, if interrupted by one minute of light every 10 minutes did
not hatch. The percent hatch in dark treatments varied significantly between nests and, in some treatments, correlated negatively
with the size of the egg clumps (number of eggs per clump) tested. To initiate hatching in the presence of light required
intensities of 0.03 lux or less. These low intensities are not reached until about 20 minutes after sunset on the reef where
the embryos occur. We conclude that hatching for some embryos occurs about 30 minutes after sunset but for most is not completed
until at least one hour after sunset. Hatching therefore takes place at a time long after potential diurnal fish predators
have refuged in the reef structure. |
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Keywords: | Fish hatching Twilight effect Demersal eggs Antipredator adaptation Hatching mechanism |
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