An attempt to extend the Habitat Harshness Hypothesis to tidal flats: A case study of Anomalocardia brasiliana (Bivalvia: Veneridae) reproductive biology

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. The results of this first attempt did not support the extension of the HHH to tidal flats. It is possible that hypotheses that take into account only physical variables may not be the most adequate for describing environments with such a high species richness and high abundance as tidal flats. Nevertheless, other studies are necessary to confidently expand or refute the HHH with regard to tidal flats, and this topic should be considered as a priority in future investigations in sandy beach ecology.