Distribution and number change of the Littorinid (Gastropoda) on intertidal hard bed in the Jiulong Estuary, Fujian Province

Among four species of Littorinid,Littorina scabra,L.brevicula,Nodiliitorina millegrana and N.pyramidalis pyramidalis,on the hard intertidal zone in the Jiulong Estuary,Fujian,L.scabra has the most extensive distribution both vertically and horizontally,and the highest anual average density.The uppermost limit of vertical distribution of N.pyramidalis pyramidalis is higher than the other three Littorinid.Desiccation is a main factor affecting the uppermost limit of vertical distribution of the Littorinid.The increasing wave action will raise the uppermost limit vertical distribution of Littorinid.With seasonal changes,the densities of the Littorinid also change in different tidal zonations.Difference in salinity is the main factor affecting the horizontal distribution of the Littorinid in the estuary.