Nursery culture of Haliotis rubra: the effect of cultured algae and larval density on settlement and juvenile production
2004
Daume, S. | Huchette, S. | Ryan, S. | Day, R.W.
In the present study we investigated the use of a green macroalga Ulvella lens on a commercial scale to improve the settlement and early growth of Haliotis rubra larvae. Two conditioning methods were evaluated comparing plates covered with U. lens grown over 4 and 18 days. An average settlement rate of 62% was estimated 3 days after larval release. This rate is amongst the highest recorded in commercial nurseries, suggesting that this technique of conditioning the settlement plates was efficient and reliable. Larvae showed a clear preference for older plates with a lower cover of U. lens. Larvae were released at two densities (50,000 and 100,000 larvae per 1000 l tank representing approximately 0.25 and 0.5 larvae cm -2 of substrate, respectively) to investigate if larval density influences overall settlement rate and later performance. Larval release density did not have a significant effect on settlement rate. After settlement, plates were randomised and the food density was enhanced. Half of the tanks were inoculated with the cultured diatom Navicula sp. and the other half received a mix of naturally developing diatom species, to determine the effect on growth and survival over a period of 4 months. We demonstrated that the type of substrate on which the larvae settled, light (which affects the food density but may also affect the oxygen level in the boundary layer of the biofilm) and the density of post-larvae have very marked effects on growth. Survival was strongly density-dependent after 64 days and the instant mortality rate (M) decreased from 43.7 in the first 10 days to 5.4 between 22 and 64 days after settlement. These results provide crucial technical and ecological information on the early development of H. rubra in the nursery and suggest that the use of U. lens will provide substantial improvements in nursery performance.
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