The cultivation of Ulva lactuca (chlorophyta) in an integrated aquaculture system, for the production of abalone feed and the bioremediation of aquaculture effluent

Significant effort has been put into the development of cost-effective abalone cultivation systems in South Africa, but the limited availability of suitable seaweed for abalone food is an obstacle to future development. The aim of this study was to investigate whether land-based integrated aquaculture (tank cultivation) and seaweed culture using Ulva lactuca in aquaculture effluent was feasible. This study was carried out at two abalone farms: Danger Point (I & J) (140 km east of Cape Town) and Jacobsbaai (JSP) (120 km north of Cape Town, South Africa). Both farms want to supplement the abalone feed with Ulva and investigate its potential for recirculation. Ulva is one of the simplest seaweeds to cultivate as it grows vegetatively. It would have a further benefit in its capacity to absorb nutrients and thus improve water quality of the aquaculture effluent. Results show that abalone effluent medium alone is insufficient for seaweed cultivation. Turbot effluent media has far more nutrients for seaweed but turbidity due to incomplete turbot feed pellet assimilation could be a problem. The most effective cultivation media on both farms is a fertilized effluent growth medium. This study established that water exchange rates are important in assuring an optimum nutrient supply for the seaweed. At high water exchange rates (20 Volume Exchanges (VE).d ·1), Specific Growth Rate (SGR) in turbot and seawater treatments were not significantly different despite a significant difference in water nutrient concentration. Maximum nutrient removal occurs at both 12 and 20 volume exchanges per day, using a stocking density of 3 kgm·2 on both farms. Approximately 70 % of the ammonium is removed during the day and 60 % at night at JSP in both turbot and abalone treatments, while at I & J in the abalone treatments, 90 % and 80 % of the ammonium is removed during the day and night respectively. The diel fluctuation in dissolved oxygen is above critical levels (6 mg.I) for abalone respiration at night, thus indicating that direct recirculation is possible. The seaweeds grown at a high water exchange rate at JSP were all phosphate limited except in winter, when background phosphate concentrations increased. Thus, fertilizers like Maxiphos can benefit the alga, especially if the phosphate ratio were to be increased in summer. Maintaining a pH below 9 is important in maintaining seaweed health and should become an integral part of the farm management protocol. Myrionema strangulans is an epiphyte newly recorded for South Africa during this project and has potentially devastating effects for culture of Ulva. Pulse fertilization of culture tanks combined with seasonal shading (late September to early February) using 20 % shade cloth controls epiphytic and fouling algal growth, particularly Myrionema. Shading also improves thallus condition, increases tissue nitrogen and decreases pH. Shading with a 50 % shade cloth however, has a significant reduction on uptake of ammonium and phosphate by the seaweed as well as decreasing the SGR and resulting in a species dominace switch from Ulva lactuca to Ulva capensis. There is a decrease in SGR when scaling up tank sizes, but this decrease can be optimized by cultivating the alga in pulse fertilized effluent water. Growing Ulva in effluent media increases its tissue nitrogen and thus protein content, increasing it above levels found in nature (average protein content in turbot= 49.8 %) and improving it as a source of protein for cultured abalone. A consistent relationship between tissue nitrogen and thallus colour was determined and can be used by mariculture farmers to assess the nutrient quality of Ulva as a food source for abalone which has important benefits for Ulva aquaculture. On the I & J farm the chosen stocking density (2 kg.m"2) produced maximum SGR and yields. At JSP the chosen stocking density {2 kg.m"2) was too high and a stocking density of 1 kg.m·2 would have optimized SGR. Seasonal effects on stocking density were not investigated. Addition of Kelpak ® concentration (commercial kelp extract) of 1: 2 500 pulse fed once a week, increases SGR. This study has shown that Kelpak® in addition to fertilizer may have commercial potential in the seaweed mariculture industry. These results confirm that Ulva is exceptionally suitable for intensive culture in different types of nutrient loaded water, and that its cultivation on an abalone farm could have significant economic benefits. For example, a 50 ton abalone farm feeding protein enriched Ulva could decrease the production time from 5 years to 3.6 year which equates to a savings of between R 800 000 - R1 300 000

Biological and economical feasibility studies of using seaweeds Ulva lactuca (Chlorophyta) in recirculation systems in abalone farming

Includes bibliographical references (p. 282-311).The aim of this study was to investigate whether a land-based recirculating seaweed-abalone integrated aquaculture system using Ulva lactuca was feasible as well as to test the differences between a commercial gravel bed recirculation system to an existing flow through system. These studies were carried out at two abalone farms: Danger Point (I & J) (140 km east of Cape Town) and at Jacobs Bay (JSP) (120 km north of Cape Town. South Africa). In both studies no significant difference in terms of water quality, abalone growth rates and abalone health were found. It was found that a seaweed /abalone recirculating system at the designed water exchange rates (25 %) was nitrogen limited and that the system as designed could be run at 75 % recirculation rate and remove a significant proportion of the dissolved nutrients (ammonium, phosphorus, nitrate and nitrite)

The cultivation of Ulva lactuca (chlorophyta) in an integrated aquaculture system, for the production of abalone feed and the bioremediation of aquaculture effluent

Includes bibliographical references (leaves 234-254).Significant effort has been put into the development of cost-effective abalone cultivation systems in South Africa, but the limited availability of suitable seaweed for abalone food is an obstacle to future development. The aim of this study was to investigate whether land-based integrated aquaculture (tank cultivation) and seaweed culture using Ulva lactuca in aquaculture effluent was feasible. This study was carried out at two abalone farms: Danger Point (I & J) (140 km east of Cape Town) and Jacobsbaai (JSP) (120 km north of Cape Town, South Africa). Both farms want to supplement the abalone feed with Ulva and investigate its potential for recirculation. Ulva is one of the simplest seaweeds to cultivate as it grows vegetatively. It would have a further benefit in its capacity to absorb nutrients and thus improve water quality of the aquaculture effluent. Results show that abalone effluent medium alone is insufficient for seaweed cultivation. Turbot effluent media has far more nutrients for seaweed but turbidity due to incomplete turbot feed pellet assimilation could be a problem. The most effective cultivation media on both farms is a fertilized effluent growth medium. This study established that water exchange rates are important in assuring an optimum nutrient supply for the seaweed. At high water exchange rates (20 Volume Exchanges (VE).d - Specific Growth Rate (SGR) in turbot and seawater treatments were not significantly different despite a significant difference in water nutrient concentration. Maximum nutrient removal occurs at both 12 and 20 volume exchanges per day, using a stocking denSity of 3 kgm-2 on both farms. Approximately 70 % of the ammonium is removed during the day and 60 % at night at JSP in both turbot and abalone treatments, while at I & J in the abalone treatments, 90 % and 80 % of the ammonium is removed during the day and night respectively. The diel fluctuation in dissolved oxygen is above critical levels (6 mg.l) for abalone respiration at night, thus indicating that direct recirculation is possible

The echinoid Parechinus angulosus and its association with other invertebrates

Echinoids are recognized as important components of temperate kelp forests because of the impact that they have by grazing. The provision of shelter by some echinoid species for both juvenile conspecifics and for other species of echinoids has been widely documented. The behaviour is thought to be important in the survival of these species. The role of echinoids as protective "nurseries" for several types of marine animals has also been suggested. Adult echinoids are supported 1 - 2 cm above the substrate by the oral spines, this leaves a gap under the echinoid where other organisms can shelter. This paper examines firstly what types of organisms associate with the echinoid Parechinus angulosus and the degree to which they display tight relationships vs. chance associations. Secondly, it explores how much selectivity of the echinoids was involved when compared to other physical shelters and open substrate. This was done by comparing differences in the species associated with level, flat rocks covered with crustose corallines; the holdfasts of Ecklonia maxima; sand, and under echinoids. The study was done at four sites in False Bay, Cape Peninsula, South Africa. Samples were collected on each habitat type by placing a bottle over the substrate and scraping the sample into the bottle. The organisms in each sample were identified under a microscope and counted. The available habitat at each site was survey by divers swimming 6 am transects and noting the cover of a particular habitat falling under the tape measure. The total number of species and organisms for each site were compared using one-way and two-way ANOVA's on untransformed data. The availability of different habitat types at each site was compared, using one-way fixed-effects ANOVA. Results showed that there was no significant difference between habitat availability at the different sites. Results of the two-way ANOVA's comparing site and habitat for individual species showed that the amphipod Paramoera capensis only occurred in significant numbers at one echinoid site. The fact that 65 % of this species had a colour variation that matched the echinoid, implied that the amphipod gains protection from predators by being associated with subtidal echinoids. This relationship is not obligate as this amphipod was found in other habitats. The echinoid Parechinus angulosus appears to have a dual habitat preference with juveniles less than 1 O mm in diameter sheltering beneath adult conspecifics and juveniles greater than 1 o mm in diameter sheltering in kelp holdfasts. The amphipod Hyale grandicomis occurred in significant numbers associated with echinoids and had a habitat preference for echinoids, suggesting that it has an important relationship with subtidal echinoids. The amphipod is a known grazer of macroalgae and thus it is possible that the amphipod gets access to a food resource in the form of drift kelp, which is trapped by the echinoid. If this is the case then the amphipod would also be gaining protection from predators by being associated with the echinoid as the amount of time it is exposed while foraging is minimal

Effects of wild and farm-grown macroalgae on the growth of juvenile South African abalone Haliotis midae Linnaeus

The effect of various macroalgal diets on the growth of grow-out (> 20 mm shell length) South African abalone Haliotis midae was investigated on a commercial abalone farm. The experiment consisted of four treatments: fresh kelp blades (Ecklonia maxima [Osbeck] Papenfuss) (~ 10 % protein); farmed, protein-enriched Ulva lactuca Linnaeus (~26 % protein) grown in aquaculture effluent; wild U. lactuca (~ 20 % protein); and a combination (mixed) diet of kelp blades + farmed U. lactuca. Abalone grew best on the combination diet (0.423 ± 0.02% weight dayˉ¹ SGR [specific growth rate]; 59.593 ± 0.02 µm dayˉ¹ DISL [daily increment in shell length]; 1.093 final CF [condition factor]) followed by the kelp only diet (0.367 ± 0.02 % weight dayˉ¹ SGR; 53.148 ± 0.02 µm dayˉ¹ DISL; 1.047 final CF), then the farmed, protein-enriched U. lactuca only diet (0.290 ± 0.02% weight dayˉ¹ SGR; 42.988 ± 0.03 µm dayˉ¹ DISL; 1.013 final CF) that in turn outperformed the wild U. lactuca only diet (-0.079 ± 0.01 % weight dayˉ¹ SGR; 3.745 ± 0.02 µm dayˉ¹ DISL; 0.812 final CF). The results suggest that protein alone could not have accounted for the differences produced by the varieties of U. lactuca and that the gross energy content is probably important.Web of Scienc

Rapid assessment of tissue nitrogen in cultivated Gracilaria gracilis (Rhodophyta) and Ulva lactuca (Chlorophyta)

Tissue nitrogen content and thallus colour were quantified using a rapid assessment method based on the Pantone® matt uncoated formula guide for raft-cultivated Gracilaria gracilis Steentoft Irvine et Farnham at Saldanha Bay and tank-cultivated Ulva lactuca Linnaeus at Jacobsbaai in 2001 – 2002. A relationship between thallus colour and tissue nitrogen, as well as a transition between green-yellows and yellow-browns that occurs between 0.8 – 1.3 mg N per g tissue (Pantone® colours 460U – 455U) for Gracilaria were found, with the green-yellow colour indicating nitrogen-starved material and the yellow-browns indicating nitrogen-replete material. For Ulva a transition between green and yellow-green occurred at a tissue nitrogen content of between 1.5 – 1.7 mg N per g tissue (Pantone® colours 585U and 583U). This relationship can be used by seaweed farmers for cultivation management as a quick guide to determine nutritional status of the seaweeds, and as an indication of protein content when the seaweeds are used as feeds.Web of Scienc

Comparing community structure on shells of the abalone Haliotis midae and adjacent rock: implications for biodiversity

This paper concerns the effects on biodiversity of depletion 24 of the South African abalone Haliotis midae, which is a long-lived species with a large corrugated shell that provides a habitat for diverse benthic organisms. We compared community structure on H. midae shells with that on adjacent rock at three sites (Cape Point and Danger Point sites A and B), and at two different times of the year at one of these sites. Shells of H. midae consistently supported communities that were distinctly different from those on rock. In particular, three species of non-geniculate (encrusting) corallines, Titanoderma polycephalum, Mesophyllum engelhartii and Spongites discoideus were all found either exclusively or predominantly on shells, whereas another non-geniculate coralline, Heydrichia woelkerlingii, occurred almost exclusively on adjacent rock. The primary rocky substratum, however, supported a higher number of species than abalone shells. Possible reasons for the differences between the two substrata include the relative age, microtopography and hardness of the substrata; the abundance of grazers on them; and the relative age of different zones of the abalone shell, which support communities at different stages of succession. Diversity on shells was lowest in zones that were either very young or very old, in keeping with the intermediate disturbance hypothesis. The distinctiveness of shell epibiota will increase diversity despite having a lower diversity than that of adjacent rock. Decimation of H. midae by overfishing therefore has implications biodiversity conservation.Web of Scienc

South African seaweed aquaculture: A sustainable development example for other African coastal countries

The green seaweed Ulva is one of South Africa's most important aquaculture products, constituting an important feed source particularly for abalone (Haliotis midae L.), and utilized as a bioremediation tool and other benefits such as biomass for biofuel production and for integrated aquaculture. Besides Ulva spp, Gracilaria spp. are also cultivated. Wild seaweed harvest in South Africa totals 7,602 mt, compared to 2,015 mt of cultivated Ulva. To mitigate for the reliance on wild harvesting, the South African seaweed aquaculture industry has grown rapidly over the past few decades. On-land integrated culture units, with paddle-wheel raceways, are now widely viewed as the preferred method of production for the industry. The success of seaweed aquaculture in South Africa is due to a number of natural and human (industrial) factors. The development of the seaweed aquaculture industry has paralleled the growth of the abalone industry, and has been successful largely because of bilateral technology transfer and innovation between commercial abalone farms and research institutions. In South Africa seaweeds have been used commercially as feedstock for phycocolloid production, for the production of abalone feed, and the production of Kelpak and Afrikelp, which are plant-growth stimulants used in the agricultural sector. Additionally, Ulva is being investigated for large-scale biogas production. The South African seaweed industry provides a template that could be used by other coastal African nations to further their undeveloped aquaculture potential

Abalone farming in South Africa: an overview with perspectives on kelp resources, abalone feed, potential for on-farm seaweed production and socio-economic importance

The South African abalone cultivation industry has developed rapidly and is now the largest producer outside Asia. With a rapid decline in wild abalone fisheries, farming now dominates the abalone export market in South Africa. Kelp (Ecklonia maxima) constitutes the major feed for farmed abalone in South Africa, but this resource is now approaching limits of sustainable harvesting in kelp Concession Areas where abalone farms are concentrated. This paper gives an overview of the development of the South African abalone industry and analyses how abalone farming, natural kelp beds and seaweed harvesting are interlinked. It discusses options and constraints for expanding the abalone industry, focussing especially on abalone feed development to meet this growing demand. Kelp will continue to play an important role as feed and kelp areas previously not utilised may become cost-effective to harvest. There are many benefits from on-farm seaweed production and it will probably be a part of future expansion of the abalone industry. Abalone waste discharges are not at present regarded as a major concern and farming brings important employment opportunities to lower income groups in remote coastal communities and has positive spill-over effects on the seaweed industry and abalone processing industry.Web of Scienc