Assessing alternative grazing-tolerant algae for nursery culture of abalone, Haliotis iris

Feeding during the nursery stage of abalone aquaculture, from larval settlement to 10 mm in shell length (SL), is a major challenge in the intensification of abalone aquaculture. Commercial abalone nurseries typically settle larvae onto vertical plastic plates coated with algae that act as a settlement cue and an important post-settlement food source. It becomes increasingly difficult to maintain an adequate algal food supply as the abalones grow and for this purpose many nurseries use the alga, Ulvella lens, as it is a very effective settlement cue as well as offering a resilient food source for the developing abalones. However, juvenile abalones can deplete a film of diatoms on the plates before they are capable of ingesting U. lens, and once abalone reach similar to 5 mm SL the high grazing pressure may exceed even what U. lens can support, requiring nurseries to provide additional cultured algae or prematurely wean the juveniles onto manufactured diets. Three prospective microfilamentous algal species isolated from the tanks of a commercial abalone facility, were selected as potentially suitable nursery algae as they demonstrated resistance to intensive juvenile grazing pressure, displayed rapid vegetative growth, and could be triggered to mass sporulate as a means of rapidly coating nursery tanks. The current study involved two experiments and assessed the suitability of each species as a live algal feed for juvenile abalones compared to U. lens. These experiments measured: (1) ingestibility and grazing resistance of each alga against juvenile abalone 1-8 mm SL, and (2) the ability of each species to recover once grazers had been removed. Two algae (Ulvophyceae sp. 1 and 3) demonstrated the desirable properties of being easily grazed by abalones of a smaller size (average SL 2.33 mm and 2.20 mm respectively) than U. lens (2.89 mm) yet provide an algal film that is likely to be resilient and durable under grazing pressure. These algae also displayed significantly greater rates of recovery following grazing than U. lens (p<0.01), an important attribute for restoring algal films in nursery systems between grazing events or between batches of juvenile abalones. The results of this study indicate that these novel algae have a combination of desirable characteristics for use in commercial abalone nurseries. Further experiments in commercial scale nursery systems should be pursued to assess the food value and performance of these species as a feed for juvenile abalones. (C) 2011 Elsevier B.V. All rights reserved.