Browsing by Author "Robertson-Andersson, Deborah"
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- ItemOpen AccessBiological and economical feasibility studies of using seaweeds Ulva lactuca (Chlorophyta) in recirculation systems in abalone farming(2006) Robertson-Andersson, Deborah; Bolton, John J; Troell, Max; Probyn, T; Smit, A JThe 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).
- ItemOpen AccessA comparison of suspended particle size and sediment loading produced by artificial and seaweed diets in integrated flow-through and re-circulating aquaculture systems on a commercial South African abalone farm(2005) Potgieter, Michelle; Bolton, John J; Troell, Max; Robertson-Andersson, DeborahThe future of abalone farming in Soulh Africa may provide benefits by the integration of abalone-seaweed re-circulation systems. This is a new system design of abalone fed on a kelp diet integrating seaweed culture facilitated by a re-circulation system. This kind of culture has the potential to increase abalone growth through increased water temperature, minimizing pumping costs while also incorporating production of on-farm seaweed resources. This has, however, the potential disadvantage to increase the suspended particulale concentration in the tank environment, with subsequent negative effects on abalone health. This study ties in with an existing Swedish-South African joint project. The results of this study will be used as inputs when trying to model a complete commercial recirculated abalone farm. Divided into two experiments this study records suspended particulate matter, particle size range and water nutrient concentrations (phosphate, ammonium and nitrite).
- ItemOpen AccessThe cultivation of Ulva lactuca (chlorophyta) in an integrated aquaculture system, for the production of abalone feed and the bioremediation of aquaculture effluent(2003) Robertson-Andersson, Deborah; Bolton, J; Anderson, R J; Probyn, TSignificant 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.
- ItemOpen AccessThe echinoid Parechinus angulosus and its association with other invertebrates(2000) Robertson-Andersson, Deborah; Branch, George MEchinoids 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.
- ItemOpen AccessSetting optimal diet ratios of kelp (Ecklonia maxima (Osbeck) Papenfuss) and formulated feed, and tests of a recirculating system using Ulva (Chlorophyta) as a biofilter, in South African abalone (Haliotis midae) cultivation(2010) Sankar, Kishan; Bolton, John J; Robertson-Andersson, DeborahLand-based abalone aquaculture in South Africa, based on the local species Haliotis midae, started in the early 1990's and has grown rapidly in the last decade. This has led to numerous studies into various aspects of farming H midae. There are two aims of this study, (i) to test the relative benefits of different ratios of kelp and the formulated feed Abfeed(R) K26 (feed component), (ii) to test the suitability of farming H midae with 50 % and 75 % recirculation rates (recirculation component) in an integrated system using the green seaweed Ulva as a biofilter. Aims for both components were to investigate the performance of the systems in terms of health of abalone, growth rates of abalone, sediment loadings and water quality. Both components were conducted on Irvin & Johnson Ltd Cape Abalone farm in Gansbaai, 140 km east of Cape Town.
- ItemOpen AccessA study of the distribution of algae in the Two Oceans Aquarium, Kelp Tank, Cape Town(2000) Robertson-Andersson, Deborah; Bolton, John J; Anderson, Robert JFive years have passed since the Two Oceans Aquarium, Cape Town, opened its doors for the first time in November 1995. Since then, a seaweed community has established itself in the Kelp tank. The seaweeds were brought in as either epiphytes on mature macro algae or as epiphytes on boulders that were placed on the floor of the tank. Thus, the community in the tank can be assumed to have established itself naturally. This study looked at the extent of the species diversity, zonation patterns in the tank (with particular reference to wall orientation), depth substrate type, plane (i.e. vertical or horizontal surfaces) and species distribution with depth. This was done by placing quadrats in transects down each wall and noting the percentage cover of each species. Quadrat depth, substrate type, wall orientation, and plane were noted. The percentage cover values as well as the environmental data were entered into CANOCO, an ordination programme for windows. Ordination showed that the tank was essentially a homogeneous environment with no difference in species distribution with regard to wall orientation, depth, substrate type, or plane. It was noted that self-seeded Ecklonia maxima were very unhealthy, small, deformed and had many epiphytes, with the exception of three plants that were growing under the plunger. From this it was concluded that water motion, and not light or nutrients, was limiting in the tank. Schimmelmannia elegans was found growing in the kelp tank. It had never been described as growing in South Africa previously. One theory was that the increased daylight length in the tank, caused by the fact that lights over the tank were often left on for extended periods, triggered a photoperiodic reproductive cue from the crustose phase (which was assumed to be growing unrecorded on the Cape Peninsular) for the sporophyte to grow. However, daylight length in the Kelp tank and Tristan da Cunha (where it was first recorded as growing) were the same so that theory was discarded. Another theory was that the algae was introduced into the tank in some way. This, however requires further investigation. Environmental conditions in the tank were investigated using aquarium records. Light intensity and duration, water temperature, pH, salinity, dissolved oxygen concentration were all found to be optimal for photosynthesis and growth to occur. Water motion was seen as the only limiting factor for photosynthesis and growth as it also has an effect on nutrient uptake. Grazer intensity was also examined. It was found that grazing by fish was stable; however, grazing by invertebrates and particularly mesa-herbivores could be increased, by adding more of them into the tank. It was found that with light being left on for functions there was no real seasonal change in light duration and this may be a problem for seaweeds that experience seasonal growth as they are missing seasonal cues. A management option of having a strictly controlled 11 hours of daylight during a winter month was proposed as a solution. This study is a good reference point for future work to be done on seaweed succession in the Kelp tank.