Zooplankton abundance in subtropical waters: Is there a lunar cycle?

Based on historical data of abundance, we report evidence of changes in zoo plankton abundance in the 0-200 m layer related to the moon cycle confirmin g that this phenomenon is produced in the marine environment, similarly to the one described for freshwater ecosystems. A clear decrease in the abunda nce of copepodites plus copepods was observed from the second to the fourth quarter of the moon when the seasonal variability was suppressed. During t he full moon phase the large zooplankton and micronekton of the deep scatte ring layers (DSL) would not reach the upper mixed layer in order to avoid p redation because of the relatively high level of illumination. Thus epipela gic zooplankton abundance increases as the effect of a lower predatory pres sure. Conversely, during the new moon phase the diel migrants reach the sur face waters and epiplankton abundance considerably decreases. Recent oceani c sediment trap data in subtropical waters indicate that the particle flux increases at about 30 days period. Thus, the effect of diet vertical migran ts could promote not only the variability in their resources and the intens ity of the active flux, but could also drive the variability in the gravita tional flux.