A series of trials was conducted to investigate the optimal temperature and light conditions for the culture of 3 benthic diatoms (Cocconeis sublittoralis, Achnanthes longipes and Navicula cf. jeffreyi), their biochemical composition as well as their suitability as a feed source for juvenile greenlip abalone (Haliotis laevigata) (4.07 ± 0.08 mm shell length) in commercial scale nursery culture over 24 wk. C. sublittoralis can grow well in a range of light intensities (830–1,217 lux) and is thus suited for the changing light conditions in a commercial abalone nursery. Achnanthes longipes grows well under high light conditions (1,412–4,400 lux) at low (18°C) and high (25°C) temperatures indicating that this species is more suited to culture in unshaded tanks and higher in the water column, on plates closer to the water surface. Cocconeis sublittoralis and Navicula cf. jeffreyi were cultured together to investigate competitive interactions between the two species. Throughout the experiment Navicula cf. jeffreyi was significantly higher in cell density when grown separately compared with the combined culture with C. sublittoralis. However when considering cell volume C. sublittoralis is substantially larger with a cell volume of 20,183 μm3 compared with 367 μm3 for N. cf. jeffreyi. Thus the cell density of N. cf. jeffreyi must be around 4 times higher than C. sublittoralis to achieve similar biomass, which was only the case at the start of the experiment. Hence N. cf. jeffreyi is a pioneer species (early colonizer) whereas C. sublittoralis is likely to eventually out compete N. cf. jeffreyi. Cocconeis sublittoralis is a suitable diatom species for commercial abalone nurseries, particularly when larger photophobic juveniles ( 5 mm shell length) are cultured and shading is often necessary. The percentage of protein was significantly higher in N. cf. jeffreyi in comparison with the other two species whereas A. longipes contained significantly higher percentage lipid. At a commercial scale juvenile abalone were successfully maintained on diatom diets for at least 18 wk (to ca. 8 mm in SL) after which growth slowed. All diatom species declined in density after week 18 coinciding with a drop in temperature from 20.38 ± 0.09°C at the beginning of the experiment to 16.23 ± 0.11°C. Juveniles feeding on N. cf. jeffreyi and A. longipes reached only 9.99 ± 3.52 and 9.49 ± 3.21 mm, respectively, in nursery tanks after 24 wk. The biomass of these later two species was lowest overall because of the small cell volume of N. cf. jeffreyi and low cell density of A. longipes. Shell length reached 10.71 ± 3.58 and 10.42 ± 3.71 mm in the C. sublittoralis and mixed diatom treatments, respectively. Speci
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Vol. 26 • No. 3