The effect of temperature on the embryonic and larval development of blacklip (Haliotis rubra) and greenlip (H. laevigata) abalone

Embryonic and larval development of Haliotis rubra and H. laevigata was observed at water temperatures of 12-2°C from fertilisation to completion of the velum. The timing of first and second cell division, prototrochal cilia formation and completion of the velum was plotted against water temperature to determine the biological zero point (BZP) (i.e., the theoretical minimum temperature below which larval development is arrested) for each species. The BZP estimate for larval development of H. rubra was 7.8°C and of H. laevigata was 7.2°C. A simultaneous experiment, in which larvae were cultured at ca. 16°C and sampled at 4 h intervals determined the effective accumulative temperature (EAT; the cumulative difference between the culture temperature and the BZP, calculated hourly) for prominent developmental stages in both species. The EAT for hatchout, torsion, eyespot formation and metamorphic competence (i.e., formation of the fourth tubule on the cephalic tentacle) for blacklip abalone was 160, 380, 590 and 1280 EAT°C-h, respectively. Corresponding figures for greenlip abalone were 180, 420, 640 and 1340 EAT°C-h, respectively. The EAT for dispersal (i.e., the difference between the EAT for metamorphic competence and that for hatchout) was 1120 and 1160 EAT°C-h for blacklip and greenlip abalone, respectively. Such information enables the prediction of the dispersal window for each species at a given temperature.