The gametogenic cycle of Scrobicularia plana (da Costa, 1778) (Mollusc: Bivalve) in Guadalquivir estuary (Cádiz, SW Spain)

Abstract The gametogenic cycle of Scrobicularia plana (da Costa, 1778) (Mollusca: Bivalvia) was studied in the Guadalquivir estuary between June 1999 and May 2000. The gonadal development was determined by means of histological methods and variations in dry weight. It is a gonochoric species. The sex ratio obtained was 1:1 ( χ 2 =0.62; P >0.05). The gametogenic cycle commenced in February and ended in October. Spawning occurred between March and September with two maximum peaks in May (97%) and July (87%). The period of sexual repose was from October to January, during which time the sex could not be determined in 64% of the population. S. plana presented a clear seasonality in its gametogenic cycle, with spawning coinciding with the highest levels of temperature, and the period of repose with the lowest levels.