Larval settlement of the Atlantic rangia,Rangia cuneata (Bivalvia: Mactridae)

Rangia cuneata larvae were given the opportunity to settle on substrate types that differed in grain size, organic content, and bacterial abundance. Larvae settled in very fine sand (63–125 μm) and fine and medium sand (125–500 μm) more than in silt and clay (<63 μm) or on a hard substratum (empty polystyrene petri dishes). Proportionally more larvae settled onto untreated sediment from the adult habitat than onto the same sediment autoclaved, or treated with either H₂O₂ to remove organic material, or treated with antibiotics to reduce bacterial abundance. However, it appears that competent larvae do not delay settlement, even in the absence of “attractive” substrates.