Fertilization biology of the abalone Haliotis laevigata:: laboratory and field studies

A combination of laboratory and field experiments with the commercial abalone species Haliotis laevigata showed that fertilization may be a limiting factor in some exploited populations when distances separating spawning individuals are too large. The effects of gamete age, gamete concentration, and gamete contact time in the laboratory were used to model fertilization success in situ and compared with experimental fertilization rates in the field. Highest fertilization rates in vitro (80%) were found for sperm concentrations in the range of 1 x 10(4) to 1 x 10(6).mL(-1). Fertilization rates of 48 +/- 1.7% (95% CI) were measured at separation distances of 2 m and dropped to 2.8 +/- 0.7% (95% CI) at 16 m downstream, agreeing closely with rates predicted by the model. Recruitment failures reported for South Australian populations of H. laevigata have occurred when densities fell below similar to 0.3 animals.m(-2), or mean nearest-neighbor distances between 1 and 2 m. This density corresponds well to critical nearest-neighbor distances for fertilization success. Stocks at higher densities are predicted to have higher fertilization rates (similar to 90%) such that fertilization success is not a factor limiting recruitment.