Growth and survival of juvenile greenlip abalone (Haliotis laevigata) feeding on germlings of the macroalgae Ulva sp

Germlings of the green alga Ulva sp. were developed as a diet for juvenile Haliotis laevigata (>= 3.5 mm shell length) and compared with a current commercial diet consisting of Ulvella lens plus the diatom species Navicula cf. jeffreyi. The utilization of macroalgae germlings (juvenile gametophyte and sporophyte) allowed 3-dimensional growth and subsequently provided greater feed biomass in comparison with the current 2-dimensional commercial feed for the later nursery phase consisting of 5-10 mm (shell length) juvenile abalone. The juvenile abalone showed active feeding on both the Ulva germling diet and the current commercial diet. The Ulvella lens/Navicula cf. jeffreyi diet resulted in abalone of significantly larger shell length at the end of the 14-wk feeding trial. However, the Ulva germling diet recorded significantly larger abalone for the first 4-5 wk, whereas the commercial diet produced significantly larger abalone from week 6 to the end of the trial. The growth rate on both diets exceeded 100 mu m.day(-1) and the specific growth rates were maintained above 1%.day(-1) for the duration of the feeding trial with neither measure portraying significant differences between diets. There was no significant difference in juvenile abalone mortality feeding on the two diets. The Ulva germling consumption exhibited a spike (500 germling blades. abalone(-1).day(-1)) in consumption at week three then, once reduced, a gradual increase occurred until the end of the trial. Ulvella lens consumption demonstrated a similar pattern to Ulva germlings consumption and was significantly, positively correlated. Consumption rates for the two green algae both correlated with juvenile abalone growth. The diatom (Navicida cf. jeffreyi) consumption was affected by plate rotation (light intensity and grazing pressure) rather than juvenile abalone.