Optimising Integrated Multitrophic Aquaculture (IMTA) on a South African abalone farm
- Authors: Falade, Abiodun Emmanuel
- Date: 2024-10-11
- Subjects: Aquaculture , Integrated multi-trophic aquaculture , Seaweed , Abalone culture South Africa , Abalones , Ingestion , Nutrient cycles
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466712 , vital:76772 , DOI https://doi.org/10.21504/10962/466712
- Description: The efficiency of fed nutrient utilisation in integrated multitrophic aquaculture (IMTA) system was evaluated on a South African abalone farm. On many commercial abalone farms in South Africa, Haliotis midae are fed a combination of pelleted feed and live macroalgae cultured downstream in abalone effluent. This production technique reduces the discharge of dissolved nutrients into the environment and improves farm productivity as unquantified proportion of the waste metabolites is captured as macroalgal biomass. However, the solid waste from abalone culture tanks remains unutilised and discharged to the coastal environments. Thus, there is scope to improve the dissolved nutrients removal efficiency of the macroalgae and to reduce the discharge of particulate nutrients using detritus waste extractive organisms. The present study aimed at the production and environmental performance of a shore-based abalone/macroalgae IMTA improving farm in South Africa by improving the nutrient utilisation efficiency of farmed abalone and seaweed and testing the waste solids removal potential of a sea cucumber species. Monoculture systems, where abalone and seaweed were cultured separately, both in fresh seawater (salinity: 35 g/L), were compared with an integrated culture system where the seaweed (Ulva lacinulata) was cultured downstream in the wastewater flowing from abalone tanks that were up-channel. Based on the findings from quantifying the performance of these production systems, methods to improve the nutrient utilisation and production efficiencies of the production systems were explored. These assessed methods included (1) the removal of abalone biodeposits by detritus extractive sea cucumber production, (2) evaluating the potential of farmed macroalgae as supplement in formulated diet, and (3) replacing mineral fertilisers with eco-friendly live microbial fertilisers for seaweed farming. Furthermore, the overall environmental performance of the two farm systems was quantified using a life cycle analysis methodology. Monitoring of the nutrient flows through the monoculture and IMTA systems revealed that the highest inputs of nutrients (nitrogen and phosphorus) into the abalone and seaweed culture tanks of the two production systems were abalone feed pellet (70-81%) and mineral fertilisers respectively (63-93%). About 48-51% of the nitrogen supplied from the feed was utilised by abalone in the IMTA and monoculture systems, while the remaining portion was lost as organic waste nitrogen on the production tank floor (20-30%) and as dissolved nitrogen in post-abalone tank effluent (30-36%). In the seaweed tanks receiving abalone effluent (IMTA), 69% of the dissolved nitrogen input was absorbed by cultured Ulva while 25% of the nitrogen was lost to the post-seaweed effluent which returned to the environment. However, in the monoculture system, 52% of the nitrogen from supplemented inorganic fertiliser was absorbed by cultured Ulva while ca. 46% of the nutrient was lost to coastal waters through the post-seaweed effluent. Moreover, while the feed accounted for ca. 74-78% input of the phosphorus in abalone of the two production systems, not more than 19% and 13% of this phosphorus was utilised by H. midae in the IMTA and monoculture systems respectively, while the largest portions were lost as organic waste in the sediment (34-45%) and dissolved waste phosphorus in the effluent (33-54%). In the seaweed tanks, a small portion (11-15%) of supplied phosphorus was removed by farmed Ulva while 77-89% was lost in the post-seaweed effluent discharged to coastal environment. The substitution of 50% mineral fertilisers with live microbial fertilisers during seaweed production significantly reduced the discharge of dissolved nitrogen and phosphorus from macroalgae raceways to coastal environment by 55 and 45% respectively, without impacting their growth, yield and nutrient compositions. A life cycle analysis of the measured energy and nutrients utilisation efficiency of these production systems was compiled, and the impacts of the inputs and outputs from each production system on the environment was assessed. The electrical energy input to abalone and seaweed tanks constituted the highest contribution to all assessed environmental impact categories for the two production systems, followed by the contributions from the nutrients supplied to farmed abalone (formulated diet) and seaweed (mineral fertilisers). The impact of these inputs on the environment was most evident on marine aquatic ecotoxicity being 2.11E+03 kg 1.4-DB eq and 4.43E+03 kg 1.4-DB eq for IMTA and monoculture systems respectively. The measured impact of seaweed aquaculture on the environment was reduced by 50-52% when Ulva was cultured in abalone effluent (IMTA) compared to culture in fresh seawater (monoculture). However, the input of chemical fertilisers in the two systems of cultivation resulted in similar eutrophication potentials (8.09 - 8.41E-02 kg PO4--- eq). To reduce the solid waste discharge from abalone tanks, and create an additional high-value crop, an endemic sea cucumber species (Neostichopus grammatus) was introduced on the floor of the abalone culture tanks in a pilot abalone/detritivore/macroalgae IMTA system. The sea cucumber utilised the biodeposits in abalone tanks as food which reduced organic solid discharge to the environment by 11%. However, the sea cucumbers displayed poor nutrient utilisation, a negative growth rate (- 0.59% day-1) and 49% weight loss by the end of the trial that was probably due to sub-optimal habitat conditions (lack of a sand substrate). The potential of including farmed Ulva (IMTA and monoculture) meal in pelleted feed for H. midae was evaluated as a means of improving farming efficiency and reducing the levels of fishmeal and soya in the pellet. In an initial trial, Ulva was included at 12% dry weight in commercial diet and fed to farmed H. midae for 244 d. The 12% inclusion of IMTA and monoculture Ulva resulted in poor feed conversion and nutrient utilisation by H. midae. In a follow-up trial which tested graded inclusion levels of Ulva meal (0.75, 1.50, 3.00, 6.00 and 12.00%), the growth rate and feed utilisation of H. midae was enhanced at a 0.75-6.00% inclusion level of the seaweed in the diet, while at a 6.00-12.00% inclusion level growth rates and feed conversion efficiencies decreased. Therefore, it is recommended that for sub-adult South African abalone, up to 6.00% IMTA Ulva meal can be included in the diet formulation without impacting their growth performance and nutrient utilisation efficiency negatively. This present study contributes to the understanding of the nutrient utilisation dynamics on integrated abalone farms in South Africa. The evidence from the different trials suggests the IMTA techniques tested could be adopted to improve the production performance and reduce the impact of abalone farming on the environment. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Falade, Abiodun Emmanuel
- Date: 2024-10-11
- Subjects: Aquaculture , Integrated multi-trophic aquaculture , Seaweed , Abalone culture South Africa , Abalones , Ingestion , Nutrient cycles
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466712 , vital:76772 , DOI https://doi.org/10.21504/10962/466712
- Description: The efficiency of fed nutrient utilisation in integrated multitrophic aquaculture (IMTA) system was evaluated on a South African abalone farm. On many commercial abalone farms in South Africa, Haliotis midae are fed a combination of pelleted feed and live macroalgae cultured downstream in abalone effluent. This production technique reduces the discharge of dissolved nutrients into the environment and improves farm productivity as unquantified proportion of the waste metabolites is captured as macroalgal biomass. However, the solid waste from abalone culture tanks remains unutilised and discharged to the coastal environments. Thus, there is scope to improve the dissolved nutrients removal efficiency of the macroalgae and to reduce the discharge of particulate nutrients using detritus waste extractive organisms. The present study aimed at the production and environmental performance of a shore-based abalone/macroalgae IMTA improving farm in South Africa by improving the nutrient utilisation efficiency of farmed abalone and seaweed and testing the waste solids removal potential of a sea cucumber species. Monoculture systems, where abalone and seaweed were cultured separately, both in fresh seawater (salinity: 35 g/L), were compared with an integrated culture system where the seaweed (Ulva lacinulata) was cultured downstream in the wastewater flowing from abalone tanks that were up-channel. Based on the findings from quantifying the performance of these production systems, methods to improve the nutrient utilisation and production efficiencies of the production systems were explored. These assessed methods included (1) the removal of abalone biodeposits by detritus extractive sea cucumber production, (2) evaluating the potential of farmed macroalgae as supplement in formulated diet, and (3) replacing mineral fertilisers with eco-friendly live microbial fertilisers for seaweed farming. Furthermore, the overall environmental performance of the two farm systems was quantified using a life cycle analysis methodology. Monitoring of the nutrient flows through the monoculture and IMTA systems revealed that the highest inputs of nutrients (nitrogen and phosphorus) into the abalone and seaweed culture tanks of the two production systems were abalone feed pellet (70-81%) and mineral fertilisers respectively (63-93%). About 48-51% of the nitrogen supplied from the feed was utilised by abalone in the IMTA and monoculture systems, while the remaining portion was lost as organic waste nitrogen on the production tank floor (20-30%) and as dissolved nitrogen in post-abalone tank effluent (30-36%). In the seaweed tanks receiving abalone effluent (IMTA), 69% of the dissolved nitrogen input was absorbed by cultured Ulva while 25% of the nitrogen was lost to the post-seaweed effluent which returned to the environment. However, in the monoculture system, 52% of the nitrogen from supplemented inorganic fertiliser was absorbed by cultured Ulva while ca. 46% of the nutrient was lost to coastal waters through the post-seaweed effluent. Moreover, while the feed accounted for ca. 74-78% input of the phosphorus in abalone of the two production systems, not more than 19% and 13% of this phosphorus was utilised by H. midae in the IMTA and monoculture systems respectively, while the largest portions were lost as organic waste in the sediment (34-45%) and dissolved waste phosphorus in the effluent (33-54%). In the seaweed tanks, a small portion (11-15%) of supplied phosphorus was removed by farmed Ulva while 77-89% was lost in the post-seaweed effluent discharged to coastal environment. The substitution of 50% mineral fertilisers with live microbial fertilisers during seaweed production significantly reduced the discharge of dissolved nitrogen and phosphorus from macroalgae raceways to coastal environment by 55 and 45% respectively, without impacting their growth, yield and nutrient compositions. A life cycle analysis of the measured energy and nutrients utilisation efficiency of these production systems was compiled, and the impacts of the inputs and outputs from each production system on the environment was assessed. The electrical energy input to abalone and seaweed tanks constituted the highest contribution to all assessed environmental impact categories for the two production systems, followed by the contributions from the nutrients supplied to farmed abalone (formulated diet) and seaweed (mineral fertilisers). The impact of these inputs on the environment was most evident on marine aquatic ecotoxicity being 2.11E+03 kg 1.4-DB eq and 4.43E+03 kg 1.4-DB eq for IMTA and monoculture systems respectively. The measured impact of seaweed aquaculture on the environment was reduced by 50-52% when Ulva was cultured in abalone effluent (IMTA) compared to culture in fresh seawater (monoculture). However, the input of chemical fertilisers in the two systems of cultivation resulted in similar eutrophication potentials (8.09 - 8.41E-02 kg PO4--- eq). To reduce the solid waste discharge from abalone tanks, and create an additional high-value crop, an endemic sea cucumber species (Neostichopus grammatus) was introduced on the floor of the abalone culture tanks in a pilot abalone/detritivore/macroalgae IMTA system. The sea cucumber utilised the biodeposits in abalone tanks as food which reduced organic solid discharge to the environment by 11%. However, the sea cucumbers displayed poor nutrient utilisation, a negative growth rate (- 0.59% day-1) and 49% weight loss by the end of the trial that was probably due to sub-optimal habitat conditions (lack of a sand substrate). The potential of including farmed Ulva (IMTA and monoculture) meal in pelleted feed for H. midae was evaluated as a means of improving farming efficiency and reducing the levels of fishmeal and soya in the pellet. In an initial trial, Ulva was included at 12% dry weight in commercial diet and fed to farmed H. midae for 244 d. The 12% inclusion of IMTA and monoculture Ulva resulted in poor feed conversion and nutrient utilisation by H. midae. In a follow-up trial which tested graded inclusion levels of Ulva meal (0.75, 1.50, 3.00, 6.00 and 12.00%), the growth rate and feed utilisation of H. midae was enhanced at a 0.75-6.00% inclusion level of the seaweed in the diet, while at a 6.00-12.00% inclusion level growth rates and feed conversion efficiencies decreased. Therefore, it is recommended that for sub-adult South African abalone, up to 6.00% IMTA Ulva meal can be included in the diet formulation without impacting their growth performance and nutrient utilisation efficiency negatively. This present study contributes to the understanding of the nutrient utilisation dynamics on integrated abalone farms in South Africa. The evidence from the different trials suggests the IMTA techniques tested could be adopted to improve the production performance and reduce the impact of abalone farming on the environment. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2024
- Full Text:
- Date Issued: 2024-10-11
Biological longitudinal aspects of the Kabompo River, a significant tributary of the upper Zambezi sub-catchment, North-west Province, Zambia
- Janse van Rensburg, Lomarie Cathleen
- Authors: Janse van Rensburg, Lomarie Cathleen
- Date: 2023-03-29
- Subjects: Nutrient cycles , Stable isotopes , Redeye Labeo , Synodontis , Zambezi River Watershed Ecology , Aquatic ecology
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422292 , vital:71928
- Description: The landscape of the Upper Zambezi Catchment in the remote North-Western Province of Zambia retains many natural features, but current and future anthropogenic activities threaten its integrity. Lack of information relating to the basic ecological functioning of the region hampers conservation efforts. Flooding from the adjacent woody-savanna and open grasslands in the Upper-Zambezi Catchment in the wet season drives crucial processes in the aquatic ecosystems such as the Kabompo River. This thesis describes aquatic food webs and describes the nutrient cycling in this river. A general introduction was based on the seasonality, river morphology, and biodiversity of the Kabompo River. There is no aquatic food web information available on this river. To address this knowledge gap, sampling of the principal food web components– vegetation, invertebrates, and fish – were collected in the dry season from August to September 2019 across six sites in the Kabompo River. Stable isotope analyses provided proxies for the food web structure at each site, and were the basis of longitudinal comparisons. The analyses suggest that the Kabompo River food webs follow the trophic ordination and nutrient cycling characteristic of the revised-Riverine Productivity Model. Food webs and community assemblages remain structurally similar between sites and provide some evidence of bottom-up productivity-driven trophic dynamics. To predict the possible landscape-scale processing of nutrient changes present for the aquatic ecosystems of the Kabompo River, a longitudinal comparison between a herbivore, Labeo cylindricus, and omnivore, Synodontis spp., fish species and their resources (primary producers and invertebrates) was done and showed archetypal fish food web trophic separation (2 ‰ to3 ‰) between species which remains consistent for the headwater sites. The nutrient values change at the convergence between the Kabompo Bridge and the Mwinilunga branches and show a decrease in the trophic separation of the sites below. This change becomes apparent from the last site, Watopa, where the trophic separation re-establishes (2 ‰ to 3 ‰) between the species. The trend suggests primarily autochthonous production in the headwater reaches, changing to allochthonous and autochthonous nutrient incorporation after the convergence of the two main branches. Permanent wetlands surrounding the convergence zones may be conducive to more primary producer activity and increased nutrient turnover. Permanent wetlands are a common feature of the Upper Zambezi Catchment tributaries, with the most notable lentic system the Barotse Flood Plains in the south, which shares reach-adjacent characteristics with the Kabompo River. Trends from the 2015 dry season identified for the Barotse Flood Plains support the findings of this thesis, where the δ13C values recorded reach depletion of -45 ‰. Management in the Upper Zambezi Basin and the Kabompo River comprises biannual assessments of water quality and quantity by the Zambezi River Authority, but not of the ecosystem process. This thesis may provide information to address the ecological (food webs and nutrient cycling) dynamics of the Basin rivers. As the first baseline information on the river's biology and ecology, it may present a comparative basis for future assessments under conservation management strategies. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Date Issued: 2023-03-29
- Authors: Janse van Rensburg, Lomarie Cathleen
- Date: 2023-03-29
- Subjects: Nutrient cycles , Stable isotopes , Redeye Labeo , Synodontis , Zambezi River Watershed Ecology , Aquatic ecology
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422292 , vital:71928
- Description: The landscape of the Upper Zambezi Catchment in the remote North-Western Province of Zambia retains many natural features, but current and future anthropogenic activities threaten its integrity. Lack of information relating to the basic ecological functioning of the region hampers conservation efforts. Flooding from the adjacent woody-savanna and open grasslands in the Upper-Zambezi Catchment in the wet season drives crucial processes in the aquatic ecosystems such as the Kabompo River. This thesis describes aquatic food webs and describes the nutrient cycling in this river. A general introduction was based on the seasonality, river morphology, and biodiversity of the Kabompo River. There is no aquatic food web information available on this river. To address this knowledge gap, sampling of the principal food web components– vegetation, invertebrates, and fish – were collected in the dry season from August to September 2019 across six sites in the Kabompo River. Stable isotope analyses provided proxies for the food web structure at each site, and were the basis of longitudinal comparisons. The analyses suggest that the Kabompo River food webs follow the trophic ordination and nutrient cycling characteristic of the revised-Riverine Productivity Model. Food webs and community assemblages remain structurally similar between sites and provide some evidence of bottom-up productivity-driven trophic dynamics. To predict the possible landscape-scale processing of nutrient changes present for the aquatic ecosystems of the Kabompo River, a longitudinal comparison between a herbivore, Labeo cylindricus, and omnivore, Synodontis spp., fish species and their resources (primary producers and invertebrates) was done and showed archetypal fish food web trophic separation (2 ‰ to3 ‰) between species which remains consistent for the headwater sites. The nutrient values change at the convergence between the Kabompo Bridge and the Mwinilunga branches and show a decrease in the trophic separation of the sites below. This change becomes apparent from the last site, Watopa, where the trophic separation re-establishes (2 ‰ to 3 ‰) between the species. The trend suggests primarily autochthonous production in the headwater reaches, changing to allochthonous and autochthonous nutrient incorporation after the convergence of the two main branches. Permanent wetlands surrounding the convergence zones may be conducive to more primary producer activity and increased nutrient turnover. Permanent wetlands are a common feature of the Upper Zambezi Catchment tributaries, with the most notable lentic system the Barotse Flood Plains in the south, which shares reach-adjacent characteristics with the Kabompo River. Trends from the 2015 dry season identified for the Barotse Flood Plains support the findings of this thesis, where the δ13C values recorded reach depletion of -45 ‰. Management in the Upper Zambezi Basin and the Kabompo River comprises biannual assessments of water quality and quantity by the Zambezi River Authority, but not of the ecosystem process. This thesis may provide information to address the ecological (food webs and nutrient cycling) dynamics of the Basin rivers. As the first baseline information on the river's biology and ecology, it may present a comparative basis for future assessments under conservation management strategies. , Thesis (MSc) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Date Issued: 2023-03-29
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