LARVAL SETTLEMENT OF THE ATLANTIC RANGIA, RANGIA-CUNEATA (BIVALVIA, MACTRIDAE)

Rangia cuneata larvae were given the opportunity to settle on substrat e types that differed in grain size, organic content, and bacterial ab undance. Larvae settled in very fine sand (63-125 mum) and fine and me dium sand (125-500 mum) more than in silt and clay (< 63 mum) or on a hard substratum (empty polystyrene petri dishes). Proportionally more larvae settled onto untreated sediment from the adult habitat than ont o the same sediment autoclaved, or treated with either H2O2 to remove organic material, or treated with antibiotics to reduce bacterial abun dance. However, it appears that competent larvae do not delay settleme nt, even in the absence of ''attractive'' substrates.