Integrated seaweed cultivation on an abalone farm in South Africa

Abstract

Land-based abalone aquaculture in South Africa, based on the local species Haliotis midae, started in the early 1990s and has grown rapidly in the last decade, with 13 commercial farms now producing over 850 t per annum. Over 6,000 t per annum of kelp Ecklonia maxima are now harvested for this purpose, and some kelp beds are reaching maximum sustainable limits. Research into seaweed aquaculture as feed (Ulva and some Gracilaria) for abalone started in the late 1990s on the southeast coast (where there are no kelp beds) using abalone waste water. A growing body of evidence suggests that a mixed diet of kelp plus other seaweeds can give growth rates at least as good as compound feed, and can improve abalone quality and reduce parasite loads. A pilot scale Ulva lactuca and abalone integrated recirculation unit using 25% recirculation was designed and built on the south west coast of South Africa using one 12,000-L abalone tank containing 13,200 15± 2.5 g abalone, connected to two 3,000-L seaweed tanks containing an initial starting biomass of 10 kg of seaweed, replicated 3 times. In an 18-month period, there were no significant differences in abalone health or growth rates, sediment build up and composition, mobile macro fauna densities and species between the recirculation or the flowthrough units. Transfer of oxygen generated by the seaweeds to the abalone tanks was poor, resulting in the recirculated abalone tanks having lower (33%) dissolved oxygen concentrations than a comparable flow-through abalone unit. Seaweed nutrient content and specific growth rates in the units were comparable to seaweeds cultivated in fertilized effluent (SGR=3.2±3.4%.day −1 ; Yield=0.2±0.19 kg.m 2 . day −1 ). Indications were that at this low recirculation ratio the seaweeds in the units were nutrient limited and that there were no negative effects to the abalone being cultivated in such a recirculation unit at this recirculation ratio.

Effects of wild and farm-grown macroalgae on the growth of juvenile South African abaloneHaliotis midaeLinnaeus

“…Wild macroalgae on the other hand, are known to have a comparatively low protein content ranging from 4 -20 % (Mercer et al 1993, Fleming et al 1996, Fleurence et al 1999, Tahil and JuinioMenez 1999, Rosen et al 2000, Bautista-Teruel et al 2002, Demetropoulos and Langdon 2004a, 2004b, Dlaza et al 2008, Robertson-Andersson et al 2008) that result in relatively slow growth in abalone (Fleming 1995b, Fleming et al 1996, Rosen et al 2000, Kruatrachue et al 2004, Lee 2004, Neori et al 2004). Previous growth studies on H. midae (Cook and Claydon 1991, Owen et al 1984, Stepto and Cook 1993, Simpson and Cook 1998) that used macroalgae as feed, have used only wild, relatively low-protein macroalgae that whether fed as single-species, or in combination as mixed diets, have never been able to produce growth comparable to that obtained with feeds relatively high in crude protein (Viana et al 1993, Fleming 1995a,b, Fleming et al 1996, Bautista-Teruel and Millamena 1999, Bautista-Teruel et al 2002, Kruatachue et al 2004, Lee 2004).…”

“…With the expansion of the abalone industry in recent years, the demand for fresh kelp has steadily grown , Francis et al 2008a). In 2003, more than 7000 tons of fresh kelp fronds were harvested (Robertson-Andersson et al 2008). By 2009, however, this demand dropped to about 5500 tons (Marine and Coastal Management, South African Department of Agriculture, Forestry and Fisheries, unpublished data), this largely due to the incorporation of formulated feeds into abalone diets over the past few years (P. Britz, Department of Ichthyology and Fisheries Science, Rhodes University, pers.…”

“…Farm-grown macroalgae have been shown to have comparatively higher protein contents than their wild counterparts , 2004, Robertson-Andersson et al 2008. This is because macroalgae remove dissolved nitrogen from aquaculture effluent resulting in a considerable increase in the alga's phosphorous and protein content (RobertsonAndersson et al 2008).…”

“…on South African abalone farms is increasing, with two such farms depending almost entirely on farm-grown macroalgae to meet the bulk of their feed requirements (Bolton 2006, Troell et al 2006, Robertson-Andersson et al 2008. The latter farms culture Ulva lactuca Linnaeus alongside Haliotis midae in an integrated mariculture system where the algae serve not only as a biological filter, but also as feed for the abalone (Bolton 2006, Troell et al 2006, RobertsonAndersson et al 2008, Bolton et al 2009.…”

Seaweed and Man

“…In a Sustainable Ecological Aquaculture effort Cascadia SEAfood even integrates sablefish with two species of bivalves, kelp, and sea urchins that feed on the fouling organisms on cages, their gonads being offered to seafood gourmets (Cross 2010;Cook and Kelly 2007). In the case of an abalone farm in South Africa, the resulting seaweed crop of Ulva lactuca can partly be used for feeding the abalone (Nobre et al 2010;Robertson-Andersson et al 2008). Since it is known that Ulva synthesizes more protein (>40% dw À1 ) with higher ammonia-N in the water, it turns out to be a valuable feed allowing Haliotis to grow significantly faster than with Ulva kept in low nitrogen concentrations and containing only 12% protein (Shpigel et al 1999).…”