A chemical cue induces settlement of Sydney rock oysters, Saccostrea commercialis in the laboratory and in the field

The physical and chemical nature of a substratum's surface, including the presence of dissolved compounds or a bacterial film, may induce the settlement of invertebrate larvae. Based on previous observations of (1) enhanced recruitment of Sydney rock oysters (Saccostrea commercialis) on concrete surfaces and (2) high alkalinity at the surface of concrete due to the leaching of calcium hydroxide (Ca(OH)(2)) from the cement, experiments were designed to test the hypothesis that a surface containing Ca(OH)(2) enhances settlement of oysters. The effect of a biofilm on settlement of Sydney rock oysters was also tested. The results obtained from the field experiment differed slightly from those obtained in the laboratory. In both the laboratory and the field, Ca(OH)(2) had a positive effect on settlement. No significant effect of a biofilm on settlement on concrete substrata was observed in either experiment a positive effect of a biofilm on substrata made with sand only or on sandstone was seen in both the laboratory and the field. For the substrata made with Ca(OH)(2) and sand, however, the effect of a biofilm was positive in the field but negative in the lab. Although the results from the lab and field experiments were similar, the discrepancy was crucial in accepting or rejecting one of the hypotheses under test. The results of the study demonstrated that (1) the effects of a biofilm on settlement vary with the substratum and (2) these oysters on respond to a chemical cue (Ca(OH)(2)) in the field. The ecological implications of the ability of larvae to select a habitat in response to chemical cues are discussed.