Abstract
We examined the diel settlement fluctuations of the subtidal barnacles Megabalanus rosa and Balanus trigonus during summer at Sakihama in Okkirai Bay, Iwate Prefecture, Japan. PVC plates were suspended vertically close to a pier wall just below low tide level and inspected every six hours. The number of settled barnacles of both species were counted together. Greater settlement occurred on the illuminated sides of the panels than on the shaded sides. The settlement rate during the 04:00-10:00 interval was highest, that in the 10:00-16:00 interval followed, and those in the 16:00-22:00 and 22:00-04:00 intervals were the lowest. On clear days, the settlement rate during the 04:00-10:00 interval was significantly higher (p<0.01) than during the 10:00-16:00 interval, but the settlement rates on cloudy or rainy days were not significantly different between the two intervals. These results indicate that a great change in illumination is more of a settlement stimulus for dark-adapted larvae than for light-adapted larvae. Effects of other environmental factors on diel and day-to-day fluctuations in settlement are discussed.
