Is annual reproduction in deep-sea echinoderms a response to variability in their environment?

The deep-sea environment has traditionally been considered as one of the least variable on the surface of the Earth^1-3. However, recent evidence^4-6 suggests that there may be a seasonal fluctuation in the physicochemical environment, and there is further evidence^7-11 that annual reproductive periodicities may occur among populations of deep-sea invertebrates. We report here evidence for annual periodicities and considerable between-species synchrony in the reproductive cycles of five deep-sea echinoderms, spawning occurring in late winter and early spring. These species also show a similar mode of early development that suggests adaptation to a seasonally varying food supply.