Growth and survival of juvenile greenlip abalone feeding on germlings of the macroalgae ulva sp

ABSTRACT Germlings of the verdant alga Ulva sp. were disentangleed as a diet for juvenile Haliotis laevigata ([greater than or equal to]3.5 mm shell length) and compared with a generally received commercial diet consisting of Ulvella len plus the diatom species Navicula cf jeffreyi. The utilization of macroalgae germlings (juvenile gametophyte and sporophyte) allowed 3-dimensional expansion and subsequently provided greater fe biomass in comparison with the popular 2-dimensional commercial feed for the later nursery phase consisting of 5-10 mm (shell length) juvenile abalone. The juvenile abalone showed active feeding upon both the Ulva germling diet and the popular commercial diet. The Ulvella lens/Navicula cf jeffreyi diet comeed in abalone of significantly larger shell extent 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 produc significantly larger abalone from week 6 to the extreme point of the trial. The extension rate on both diets go beyonded 100 [micro]m.[day.sup.-1] and the specific development rates were maintained above 1%.[day.sup.-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 upon the two diets. The Ulva germling consumption exhibited a spike (500 germling blades.[abalone.sup.-1].[day.sup.-1]) in consumption at week three then, one time reduced, a gradual increase occurr until the extremity of the trial. Ulvella len consumption demonstrated a similar pattern to Ulva germlings consumption and was significantly, positively correlated. Consumption rates for the sum of two units green algae both correlated with juvenile abalone growing The diatom (Navicula cf. jeffreyi) consumption was affected through plate rotation (light intensity and grazing pressure) rather than juvenile abalone.

lock opener WORDS: juvenile abalone, Haliotis laevigata, Ulva, germlings, Ulvella len diatoms, dietary value

INTRODUCTION

To agriculture quality abalone to commercial harvest size within an economical time frame, popular culture protocols and in particular, juvenile nutrition ne to be improved. To advance this area of production, of recent origin juvenile diets must be explored that provide sufficient biomass and provide greater nutritional benefits.

The main diet of postlarval and early juvenile abalone (up to -5 mm) in the natural environment consists of epiphytic and epilithic diatoms, crustose coralline algae, sod algae and bacteria, whereas larger juveniles destroy macroalgae (Dunstan et al. 2002 Kawamura et al. 1995 Kawamura 1996 Kawamura & Takami 1995 McShane et al. 1994 Takami et al. 1998) one time abalone reach the transition phase from a diatom-based diet to a macroalgae diet, diatoms of the like kind as Cylindrotheca closterium (Ehrenberg) alone are no longer sufficient to maintain adequate increase rates in an aquaculture a whole (Takami et al. 2003). At this stage additional algal regimen is required to sustain maximum development rates and reduce the variability of increase and survival rates. Maintenance of an adequate victuals supply to the 5-10 mm juveniles is seen as a major limiting factor in the intensification of abalone nurseries (Krsinich et al. 2000)

popularly in Australian commercial abalone nurseries, postlarvae are supplied with diatoms (eg Navicula cf jeffreyi) and as they exhibit into juveniles they are provided with the crustose virid alga Ulvella lens crouch (Daume & Ryan 2004 Daume et al. 2004) U len has been shown to induce higher adjustment rates of abalone larvae compared with monospecific benthic diatom films (Daume et al. 2000 Krsinich et al. 2000) by means of itself U. lens only supports moderate growing rates but, when combined with an easily digestible diatom like as N. jeffreyi, the diet can sustain high expansion rates (Daume & Ryan 2004 Kawamura et al. 1998) Takami et al. (1997) also ground that rapid abalone growth is alone achievable on crustose coralline algae (Lithophyllum yessoense) if diatoms are at hand Once abalone exceed about 5 mm in longitudinal dimensions the combined diet of U len and N jeffreyi is unable to adequately support the high abalone biomass by plate (Daume & Ryan 2004)

A potential alternative commercial fe for juvenile abalone (5-10 mm) may be macroalgae sporelings. The majority of juvenile abalone dietary studies have been leadershiped with mature macroalgae; however, they may have different nutritional and structural properties to juvenile macroalgae of the same species (Van Alstyne et al. 1999) The juvenile macroalgae (germlings) can potentially provide a greater biomass for plate because of their 3-dimensional morphology compared with the 2-dimensional encrusting algae and have been shown to support moderate to rapid increase of 90-130 [micro]m.[day.sup.-1] (Maesako et al. (1984) as cited in Kawamura et al. (1998))

The 3-dimensional growing reduces the surface area required and gives the fe the potential to combat the juvenile abalone's ability to squander 5% to 30% of their material substance weight in algae each day (Corazani & Illanes 1998 Hahn 1989) Ulva bas been used in numerous studies, one as well as the other individually or as part of mixed/rotation diets on the contrary is considered a relatively poor nutrition source (Simpson & prepare for the table 1998). Shpigel et al. (1999) bas shown that specific development rates of 0.6 to 1%.[day.sup.-1] can be attained for juveniles 8-15 mm in shell extent and that some abalone species expand better on Ulva cultured in high ammonia-N enriched seawater, underlying the importance of the feed's nutritional value.