The annual cycle of sexual reproduction in the sea anemone Metridium senile

Abstract

The seasonal timing of sexual reproduction of Metridium senile, a sea anemone occurring intertidally and subtidally on the coast from central California to Alaska, was studied at Bodega Bay, Sonoma County, California. Individuals reproduce asexually by the regeneration of fragments torn from the pedal disc and populations consist of clones of various size and extent. Histological examination of specimens collected monthly from December 1976 to November 1979 demonstrated an annual cycle of sexual reproduction. In females, oocyte size and relative gonad size increased steadily from fall to late summer and peaked in August of each year. In males, recording the most advanced stage of spermatogenesis in each individual revealed a distinct annual cycle of gonadal maturation in 1977, but the seasonal pattern was obscured in 1978 and 1979 by the early appearance and prolonged persistence of sperm. Gonadal maturation was asynchronous among three populations studied (one harbor float and two intertidal), but the spawning of males and females in all three populations occurred between the September and October collections in each year.