POSTSETTLEMENT DISPERSAL AND DYNAMIC REPOPULATION Of ESTUARINE HAbITATS bY ADULT mercenaria mercenaria, ST. CATHERINES ISLAND

Jennings and Hunt (2009: 76) note that “postlarval or juvenile dispersal is important because for many species this is a last chance to migrate to their adult location (Hiddink and Wolff, 2002) as mobility often decreases with increasing size.”2 Postsettlement passive transport and recruitment of nonsessile bivalves under rigorous hydrodynamic conditions is not a new observation, although it was little explored back in 1991 when Emerson and Grant described it for populations of mya arenaria and when we initiated study of selected mercenaria mercenaria populations on St. Catherines Island. Since the early 1990s, postsettlement dispersal has been documented in several other bivalve species, including macoma balthica, Gemma gemma, corbicula japonica, austrovenus stuchburyi, and macomona liliana (Gunther, 1991; Norkko et al., 2001; Hunt and Mullineaux, 2002; Petuha, Lundquist, and Pilditch, 2006; bowen and Hunt, 2009, among others). These studies have documented postsettlement transport of juvenile bivalves (see discussion by Jennings and Hunt, 2009), either the result of resuspension in the water column or bedload transport (e.g., the dispersal of small juveniles of the New Zealand tellinid macomona liliana over distances of several kilometers on a single spring tide and the bedload transport of larger juveniles over tens of meters on a single tide; Petuha, Lundquist, and Pilditch, 2006). Hunt, fugate, and Chant (2009) noted that even bedload transport of juvenile bivalves could achieve, over time, cumulative net displacements of kilometers. Many studies have also noted that postsettlement dispersal of some bivalve species can also be influenced by morphology and behavior, such as the depth of burrowing, the employment of byssal threads (beukema and de Vlas, 1989), and the use of mucoid drogue lines (Prezant and Chalermat, 1984). Significant postsettlement dispersal of sedentary adult bivalves has seldom been reported, although as early as 1955 Dow and Wallace described storm-induced large-scale passive redistribution of intertidal populations of m. mercenaria in coastal Maine.