The Habitat Harshness Hypothesis (HHH) predicts that populations inhabiting the intertidal area of a dissipative beach should produce more gametes and have a longer reproductive cycle than those inhabiting an intermediate or reflective beach. This hypothesis was proposed for the exposed morphodynamic continuum between the reflective and dissipative states; however, no attempt has been made thus far to verify whether the HHH is valid for tidal flats. In this study, we analysed the reproductive cycle of Anomalocardia brasiliana in an intermediate beach and in a tidal flat and compared the results to determine whether the reproductive cycles of A.brasiliana were in agreement with the predictions of the HHH and to examine the possibility of extending this hypothesis to tidal flats. A continuous spawning season and synchrony between sexes were observed at both sites, although the reproductive effort was higher in the intermediate beach. 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