Weak synchrony in the timing of larval release in upwelling regimes

Abstract

Intertidal crabs in diverse habitats worldwide release larvae synchronously during noc- turnal spring high tides. This expedites seaward transport of the larvae to beyond high density areas of predatory fishes under the cover of darkness. We found that 4 species of intertidal crabs along the west coast of the USA shared this reproductive timing pattern. As in other mixed semidiurnal tidal regimes, biweekly patterns of larval release were more closely synchronized with the tidal amplitude cycle than the lunar cycle, and some crabs released larvae in daylight. However, unlike other places in the world, larval release was weakly synchronized to environmental cycles regardless of interspe- cific differences in vertical distributions on the shore. We provide evidence that weak synchrony in the timing of larval release in upwelling regimes can result from exposure to environmental variation over long incubation periods of externally brooded embryos. According to the prevailing paradigm, weaker synchrony in the timing of larval release will increase predation by planktivorous fishes in upwelling regimes. Weak synchrony in the timing of larval release should increase larval mortality in a wide array of animals that brood embryos in the intertidal zone, regardless of the selective force operating, and it could contribute to recruitment limitation in upwelling regimes.