Research using culture-dependent methods demonstrated that Achromobacter, Aeromonas, Altermonas, Pseudomonas,Flavobacterium/Cytophaga, Micrococcus, and Vibrio were bac- terial genera commonly isolated from bivalves (Colwell & Liston 1960, Vasconcelos & Lee 1972, Pillai 1980, Kueh & Chan 1985, Olafsen et al. 1993, Pujalte et al. 1999). Findings also indicated that bacterial concentrations in bivalves are higher by an order of magnitude than those in seawater, and dominance of culturable bacteria is classically linked to sea- sonality and water temperature (Motes et al. 1998, Cavallo et al. 2009, Zurel et al. 2011). More recent culture-independent work has shown that although these genera are commonly present, they do not necessarily represent most of the com- munity (Romero et al. 2002, Winters et al. 2010, Wegner et al. 2013, Trabal et al. 2014, Li & Wang 2017, Pierce & Ward in review).