Further observations on lunar periodicity.

Abstract

SUMMARY. The prawns Anchistioides antiguenais, Penaeopsis goodei, and Penaeopsis smithi come to the surface at regular intervals through the year about an hour after sunset. The intervals coincide with the time of the new moon, but the numbers reach a maximum on the second night of the lunar month and again on the twenty-sixth night. Penaeopsis has a seasonal fluctuation, the numbers being greatest in the summer (June, July, and August), while Anchistioides is less frequent in July and August and again from December to March. The summer reduction is due to the dying out of a generation in July; the winter scarcity to seasonal conditions. Some data are given suggesting a growth periodicity in Anchistioides, the moults among captive adults occurring more frequently from the eighteenth to the twenty-second day, and again on the twenty-eighth day than at other times during the lunar month. The factors controlling periodicity are again reviewed, and the effect of light selected as the most likely one, inhibiting the activity of the prawns, but being occasionally subject to interference by non-regular conditions such as the opacity of the water. Observations on Penaeus brasiliensis, Periclimenes americanus, and Leander affinis show that these prawns are subject to similar control. Preliminary work on periodicity in the plankton by standard tow-netting is described.