Meeting Abstract

30.1  Friday, Jan. 4  Extreme synchrony, amplitude modulation and phase reversals in the semilunar reproductive cycle of the intertidal false limpet Siphonaria gigas on a rocky shore in Panama CHRISTY, JOHN H; Smithsonian Tropical Research Institute christyj@si.edu

Many intertidal organisms produce gametes or larvae once or twice each lunar month when tidal conditions most favor survival of these vulnerable early life stages. On shores with semidiurnal tides, the changing phase relationship between the lunar synodic (29.53 days) and anomalistic (27.55 days) cycles modulates the amplitude between successive spring and neap tides. Approximately every 7 months the amplitude difference changes from one half-lunar phase to the other (e.g., switches from new to full moon, or first to last quarter, and then reverses 7 months later). I continuously monitored the semilunar cycle of egg production by the false limpet Siphonaria gigas for 4.5 years and found that this simultaneous hermaphrodite tracks this complex tidal pattern. Individuals attached ribbons of eggs in jelly whorls to the rock over a two-day period twice each lunar month with most eggs deposited 1 day before the lowest neap tides. Eggs hatched to veliger larvae in 4 – 6 days. The intensity of reproduction varied inversely with the heights of the neap tides. Consequently eggs were covered by the tide for the least amount of time before they hatched. When the difference in heights between successive neap tides was large, the limpets produced eggs only on the neap set with lower high tides. Every 7 months when the neap tide height difference shifted between the first and last quarter moons the limpets too shifted their timing, but not immediately, leading to two or more out-of-phase egg deposition cycles. Extreme synchrony and precise timing of egg deposition to correspond with the lowest tides in the month may protect eggs best from predation by fish.