LUNAR CONTROL OF EPITOKAL SWARMING IN THE POLYCHAETE PLATYNEREIS-BICANALICULATA (BAIRD) FROM CENTRAL CALIFORNIA

Lunar control of epitokal swarming in the polychaete Platynereis bican aliculata (Baird) was tested in laboratory experiments employing artif icial moonlight. Worms were exposed to the following daylength and lun ar conditions: A) in-phase daylengths with: i) artificial moonlight fo r 6-7 nights/month centered near ambient full moon, ii) centered near ambient new moon, and iii) constant ''moonlight'', and B) in-phase day lengths with: i) artificial moonlight for 14 nights/month during the p eriod of ambient full moon, ii) centered near ambient new moon, and ii i) constant ''moonlight.'' Worms exposed to artificial moonlight for 6 -7 nights in phase with full moon swarmed only on ''moonless'' nights. Those exposed to ''moonlight'' out of phase with full moon showed fie ld entrainment (swarming during the period of ambient new moon) for th e first month, then swarming mainly on ''moonless'' nights. The patter n of swarming of worms held under continuous ''moonlight'' suggests a possible circa-semi-lunar rhythm. Exposure to 14 nights (during ambien t full moon and new moon) of ''moonlight'' resulted in entrainment for the first 2 months, followed by a 1-month period of ''adjustment'' or ''clock re-setting'' to the imposed pattern of artificial moonlight, thereafter, a pattern of swarming mainly on ''moonless'' nights. These results suggest that individuals of P. bicanaliculata have an endogen ous rhythm entrained by moonlight which is manifested in a circa-lunar swarming rhythm, and the gradual decline in illumination from full mo on to last quarter moon is probably the cue that synchronizes swarming at the population level. This is the first experimental evidence of l unar-synchronized reproductive rhythm in a marine invertebrate from th e west coast of North America.