Gonad development in seeded Haliotis laevigata: Growth environmentdetermines initial reproductive investment

摘要

Cultured Haliotis laevigata (Donovan), 18 mo old, were tagged and seeded at either high or low densities on boulder reefs (4-6 m depth) at Cape Jervis, South Australia in September 2001. Surveys every 3 mo quantified growth history and a sample was sacrificed in September 2002, prior to the expected spawning season of H. laevigata from this area, to measure gonad development. This provided a unique opportunity to investigate the onset of reproductive investment in known age H. laevigata in the field. Forty-five percent of sampled abalone had developed gonad tissue by September 2002. Larger individuals were more likely to have initiated gametogenesis and tended to have larger gonads. Gonad development was most closely related to abalone weight in September 2002 and was also strongly correlated with length and early growth rate. A significant proportion of abalone migrated from cryptic positions within boulder habitats into more exposed adult habitat at the outer edge of reefs between April and June. Abalone that had emerged to adult habitat were significantly more likely to be mature than cryptic individuals. The overall proportion of abalone with developing gonads differed significantly between densities. This seems to be an indirect effect, arising because abalone at low density grew faster than those at high density. The onset of sexual maturation in H. laevigata was thus partly dependent on density and site characteristics, which probably reflect the relative availability and quality of food. The results suggest that onset of sexual maturity in H. laevigata can advance under conditions of fast growth. As sampled gonads contained ripe gametes and maturity appears to be related to growth rate, fast growing abalone may reproduce greater than or equal to 1 y before smaller juveniles in the same cohort.