Does lunar cicle affect clawed lobster egg hatching and moulting freque ncy of hatchery-reared juveniles?

Evidence that lunar cycles entrain crustacean biological rhythms is briefly reviewed. Egg laying and hatching undergo semi-lunar and monthly rhythms that appear to depend on endogenous clocks. Lunar cycles can be understood in terms of adaptation and life history. Original data are presented for Homarus gammarus (L) post larvae (n=150) hatched during March 1997 and reared artificially. Their moulting frequency was monitored from day 112 (post-hatch) to day 204 (CL=20mm±1.5 SD). Daily moults (n=253) - recorded individually during July, August and September - showed an average duration for the first and the second inter-moult interval of about 36.2 and 34 days, respectively. Daily moulting frequency distribution showed a trend characterised by peak values around the new moon weeks (n=75), and significantly lower values around the full moon weeks (n=46). Individually reared berried-lobsters hatched eggs within restricted periods in the weeks before and around new moon and full moon in the absence of any tidal cue. The pattern for communally reared female lobsters is more confusing, possibly due to inter-individual communication and natural sea temperature affecting the rhythm. However, modal and moving average values over a 24 years sampling period support the presence of a semi-lunar cycle. The cycle is maintained under laboratory conditions and in sublittoral populations that are not subjected to large tidal excursions. Therefore, the circa-lunar rhythm may represent a powerful clock that is retained for synchronising events throughout the life history of crustaceans. It results in reduced predation risks for hatchlings in dark new moon nights and favours dispersal during spring tides due to tidal currents. This may enhance mutual protection against cannibalistic habits for simultaneously moulting juveniles.