# Circularity Assessment in Aquaculture: The Case of Integrated Multi-Trophic Aquaculture (IMTA) Systems

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## Abstract

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**Key Contribution:**Specific methodology is developed to evaluate multi-trophic aquaculture (IMTA) systems from a circularity perspective. The benefits of IMTA compared to monoculture are quantified in terms of the bioremediation of nutrients and the efficient use of resources.

## 1. Introduction

## 2. Materials and Methods

#### 2.1. IMTA Laboratories

#### 2.1.1. Irish IMTA Lab

#### 2.1.2. Brazilian IMTA Lab

^{3}of FW of shrimp, 13.4 kg/m

^{3}of FW of tilapia, and 2 kg/m

^{3}of FW of seaweed.

#### 2.1.3. South African IMTA Lab

^{3}D-ended Ulva paddle raceway and multiple abalone raceway tanks (each 8.5 m

^{3}) arranged in six rows, with each row housing seven abalone raceway tanks. The effluent water from the abalone tanks in each cluster flows into the adjacent Ulva paddle raceway, where it is bioremediated (removal of N and P) by the Ulva [45] and mixed with 50% fresh seawater in the sump before being returned to the abalone raceway tanks. The continuous circulation of seawater through these tanks and Ulva paddle raceways ensures a steady supply of cool and aerated water for the growing abalone. Experiments in the SA IMTA lab were carried out to monitor the physical and chemical parameters of the abalone–Ulva IMTA system with increasing (50, 75, and 100%) recirculation rates [27].

#### 2.2. Circularity Assessment Methodology

#### 2.2.1. Nutrient Management Metrics

- Bioremediation in the Irish IMTA lab

- Bioremediation in the Brazilian IMTA lab and SA IMTA lab (abalone)

- Bioremediation in the SA IMTA lab urchin trial

#### 2.2.2. Resource Use Efficiency

## 3. Results

#### 3.1. Irish IMTA Lab

#### 3.1.1. Nutrient Management

#### 3.1.2. Resource Use Efficiency

^{−1}kWh/kg of biomass harvested, whereas the energy within the fuel consumed under IMTA conditions was slightly lower (2.52 × 10

^{−1}kWh/kg of biomass harvested), as derived from a previous LCA study [53].

#### 3.2. Brazilian IMTA Lab

#### 3.2.1. Nutrient Management

#### 3.2.2. Resource Use Efficiency

#### 3.3. South African IMTA Lab (Abalone System)

#### 3.3.1. Nutrient Management

#### 3.3.2. Resource Use Efficiency

#### 3.4. South African IMTA Lab (Urchin System)

#### 3.4.1. Nutrient Management

#### 3.4.2. Resource Use Efficiency

#### 3.5. Circularity Performance of IMTA Labs

## 4. Discussion

_{2}sequestration by mollusk shells was excluded from this study, as that is still controversial [59].

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Irish IMTA lab design: the low-trophic grid with oysters, seaweeds, and urchins lies adjacent to the salmon pens within the licensed aquaculture site.

Case Study | Monoculture | IMTA | |
---|---|---|---|

Irish IMTA lab | Salmon marine cages | Salmon marine cages with seaweed longlines and urchin and oysters in baskets | |

Brazilian IMTA lab | White shrimp in ponds | White shrimp with tilapia and seaweed in closed BFT | |

South African IMTA lab | Semi-closed abalone system | Semi-closed abalone and seaweed system | |

Semi-closed urchin system | Semi-closed urchin and seaweed system |

FMA Composition | % |
---|---|

Crude protein | 47.4 |

Lipids | 16.3 |

Linoleic acid | 2.1 |

Phospholipids | 3.5 |

Cholesterol | 0.3 |

HUFA | 1.7 |

Fiber | 0.9 |

Ash | 16.2 |

Calcium | 5.7 |

Total phosphorus | 3.0 |

Total lysine | 3.9 |

Total cysteine | 0.9 |

Total methionine | 1.4 |

Pillar | Indicator Name | Indicator Formula | |
---|---|---|---|

Nutrient management | Bioremediation | $\frac{\mathrm{C},\mathrm{N},\mathrm{P}\mathrm{e}\mathrm{m}\mathrm{i}\mathrm{t}\mathrm{t}\mathrm{e}\mathrm{d}\mathrm{b}\mathrm{y}\mathrm{f}\mathrm{e}\mathrm{d}\mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{s}}{\mathrm{C},\mathrm{N},\mathrm{P}\mathrm{t}\mathrm{a}\mathrm{k}\mathrm{e}\mathrm{n}\mathrm{u}\mathrm{p}\mathrm{b}\mathrm{y}\mathrm{e}\mathrm{x}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{v}\mathrm{e}\mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{s}}$ | (1) |

Resource use efficiency | Feed | FCR $\u230a\frac{\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}\mathrm{f}\mathrm{e}\mathrm{e}\mathrm{d}}{\mathrm{b}\mathrm{i}\mathrm{o}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{w}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t}\mathrm{g}\mathrm{a}\mathrm{i}\mathrm{n}}\u230b$ | (2) |

$\frac{\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{n}\mathrm{g}\mathrm{r}\mathrm{e}\mathrm{d}\mathrm{i}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{s}\left(\mathrm{g}\right)\mathrm{f}\mathrm{r}\mathrm{o}\mathrm{m}\mathrm{v}\mathrm{a}\mathrm{l}\mathrm{o}\mathrm{r}\mathrm{i}\mathrm{z}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{r}\mathrm{o}\mathrm{u}\mathrm{t}\mathrm{e}\mathrm{s}}{\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{o}\mathrm{f}\mathrm{f}\mathrm{e}\mathrm{e}\mathrm{d}\mathrm{d}\mathrm{e}\mathrm{l}\mathrm{i}\mathrm{v}\mathrm{e}\mathrm{r}\mathrm{e}\mathrm{d}}\times $100 | (3) | ||

Water | $\frac{\mathrm{W}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{r}\mathrm{e}\mathrm{c}\mathrm{i}\mathrm{r}\mathrm{c}\mathrm{u}\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{d}\left({\mathrm{m}}^{3}\right)}{\mathrm{W}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{n}\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{m}\left({\mathrm{m}}^{3}\right)}\times 100$ | (4) | |

Energy | $\frac{\mathrm{k}\mathrm{W}\mathrm{h}\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{u}\mathrm{m}\mathrm{e}\mathrm{d}}{\mathrm{b}\mathrm{i}\mathrm{o}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{h}\mathrm{a}\mathrm{r}\mathrm{v}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{d}}$ | (5) | |

Infrastructure | $\frac{\mathrm{k}\mathrm{g}\mathrm{i}\mathrm{n}\mathrm{f}\mathrm{r}\mathrm{a}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{u}\mathrm{c}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{e}\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{s}}{\mathrm{b}\mathrm{i}\mathrm{o}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{h}\mathrm{a}\mathrm{r}\mathrm{v}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{d}}$ | (6) |

Emitted | Absorbed | ||||
---|---|---|---|---|---|

Nutrients (kg) | Salmon ^{(1)} | Alaria | Saccharina | Oyster | Urchin |

Dissolved N | 7.18 × 10^{−2} | 1.40 × 10^{−4 (2)} | 8.05 × 10^{−5 (2)} | - | - |

Dissolved P | 1.82 × 10^{−2} | 1.97 × 10^{−4 (2)} | 1.97 × 10^{−4 (2)} | - | - |

Dissolved C | 1.14 × 10^{−2} | 1.77 × 10^{−3 (3)} | 1.28 × 10^{−3 (3)} | - | - |

Particulate N | 5.57 × 10^{−3} | - | - | 1.12 × 10^{−6 (2)} | 1.89 × 10^{−5 (4)} |

Particulate P | 1.03 × 10^{−1} | - | - | 2.99 × 10^{−6 (2)} | 1.89 × 10^{−6 (4)} |

Particulate C | 1.82 × 10^{−2} | - | - | 6.40 × 10^{−5 (4)} | 1.08 × 10^{−4 (4)} |

Shrimp Tank | Tilapia Tank | Ulva Tank | ||||
---|---|---|---|---|---|---|

Parameter | Inlet (mg/L) | Outlet (mg/L) | Inlet (mg/L) | Outlet (mg/L) | Inlet (mg/L) | Outlet (mg/L) |

Ammonia | 0.80 | 1.00 | 1.00 | 1.50 | 1.50 | 0.80 |

Nitrate | 13.00 | 15.00 | 15.00 | 16.00 | 16.00 | 13.00 |

Nitrite | 0.80 | 1.00 | 1.00 | 1.30 | 1.30 | 0.80 |

Phosphate | 1.00 | 4.00 | 4.00 | 4.10 | 4.10 | 1.00 |

TSS | 380.00 | 450.00 | 450.00 | 400.00 | 400.00 | 380.00 |

Abalone Tank | Ulva Tank | |||
---|---|---|---|---|

Parameter | Inlet (mg/L) | Outlet (mg/L) | Inlet (mg/L) | Outlet (mg/L) |

Ammonia | 0.29 | 0.41 | 0.41 | 0.29 |

Nitrate | 1.16 | 1.34 | 1.34 | 1.16 |

Nitrite | 0.20 | 0.23 | 0.23 | 0.20 |

Phosphate | 0.52 | 0.58 | 0.58 | 0.52 |

Production Systems | Feeding Regime | Feed Description | Ingredient (Description and Origin) | FCR |
---|---|---|---|---|

Abalone monoculture and Abalone–Ulva | Feed 1 | Formulated feed from specialized aquatic feed (SAF) | Not available | 1.4 |

Feed 2 | Wild-harvested kelp (Ecklonia maxima) | Wild-harvested | 12.5 | |

Abalone–Ulva | Feed 3 | IMTA-grown Ulva lacinulata | Grown in IMTA | 5 |

Production System | Feeding Regime | Feed Description | Ingredient (Description and Origin) | % (Dry Weight) | FCR |
---|---|---|---|---|---|

Urchin monoculture | Feed 1 | Formulated feed supplemented with 20% dried Ulva lacinulata | Wheat bran | 0.321 | 0.4 |

Maize (extruded) | 0.321 | ||||

Fish meal | 0.153 | ||||

Soybean | 0.153 | ||||

Di-Calcium phosphate | 0.0184 | ||||

Lecithin (de-oiled) | 0.0138 | ||||

Vitamin and mineral premix | 0.011 | ||||

Fish oil | 0.00963 | ||||

Urchin-Ulva | Feed 1 | Fresh Ulva lacinulata for the first 4 months of the production cycle | Not applicable | 1.3 | |

Feed 2 | Formulated feed supplemented with 20% dried Ulva lacinulata for the final 3 months of the production cycle | Wheat bran | 0.321 | 0.4 | |

Maize (extruded) | 0.321 | ||||

Fish meal | 0.153 | ||||

Soybean | 0.153 | ||||

Di-Calcium phosphate | 0.0184 | ||||

Lecithin (de-oiled) | 0.0138 | ||||

Vitamin and mineral premix | 0.011 | ||||

Fish oil | 0.00963 |

Indicator Name | Circularity Performance When: |
---|---|

Bioremediation | ${\left(\mathrm{B}\mathrm{I}\mathrm{O}\mathrm{R}\mathrm{E}\mathrm{M}\mathrm{E}\mathrm{D}\mathrm{I}\mathrm{A}\mathrm{T}\mathrm{I}\mathrm{O}\mathrm{N}\mathrm{C},\mathrm{N},\mathrm{P}\right)}_{\mathrm{I}\mathrm{M}\mathrm{T}\mathrm{A}}-{\left(\mathrm{B}\mathrm{I}\mathrm{O}\mathrm{R}\mathrm{E}\mathrm{M}\mathrm{E}\mathrm{D}\mathrm{I}\mathrm{A}\mathrm{T}\mathrm{I}\mathrm{O}\mathrm{N}\mathrm{C},\mathrm{N},\mathrm{P}\right)}_{\mathrm{M}\mathrm{o}\mathrm{n}\mathrm{o}\mathrm{c}\mathrm{u}\mathrm{l}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{e}}0$ |

Feed | $\u230a\frac{{\mathrm{F}\mathrm{C}\mathrm{R}}_{\mathrm{m}\mathrm{o}\mathrm{n}\mathrm{o}\mathrm{c}\mathrm{u}\mathrm{l}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{e}}-{\mathrm{F}\mathrm{C}\mathrm{R}}_{\mathrm{I}\mathrm{M}\mathrm{T}\mathrm{A}}}{{\mathrm{F}\mathrm{C}\mathrm{R}}_{\mathrm{m}\mathrm{o}\mathrm{n}\mathrm{o}\mathrm{c}\mathrm{u}\mathrm{l}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{e}}}\u230b>0$ |

${\mathrm{L}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{a}\mathrm{r}\mathrm{i}\mathrm{t}\mathrm{y}}_{\mathrm{M}\mathrm{o}\mathrm{n}\mathrm{o}\mathrm{c}\mathrm{u}\mathrm{l}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{e}}-{\mathrm{L}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{a}\mathrm{r}\mathrm{i}\mathrm{t}\mathrm{y}}_{\mathrm{I}\mathrm{M}\mathrm{T}\mathrm{A}}0$ | |

Water | ${\mathrm{W}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{r}\mathrm{e}\mathrm{c}\mathrm{i}\mathrm{r}\mathrm{c}\mathrm{u}\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}_{\mathrm{I}\mathrm{M}\mathrm{T}\mathrm{A}}-{\mathrm{W}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{r}\mathrm{e}\mathrm{c}\mathrm{i}\mathrm{r}\mathrm{c}\mathrm{u}\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}_{\mathrm{M}\mathrm{o}\mathrm{n}\mathrm{o}\mathrm{c}\mathrm{u}\mathrm{l}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{e}}0$ |

Energy | ${\left(\frac{\mathrm{k}\mathrm{W}\mathrm{h}\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{u}\mathrm{m}\mathrm{e}\mathrm{d}}{\mathrm{b}\mathrm{i}\mathrm{o}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{h}\mathrm{a}\mathrm{r}\mathrm{v}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{d}}\right)}_{\mathrm{M}\mathrm{o}\mathrm{n}\mathrm{o}\mathrm{c}.}-{\left(\frac{\mathrm{k}\mathrm{W}\mathrm{h}\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{u}\mathrm{m}\mathrm{e}\mathrm{d}}{\mathrm{b}\mathrm{i}\mathrm{o}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{h}\mathrm{a}\mathrm{r}\mathrm{v}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{d}}\right)}_{\mathrm{I}\mathrm{M}\mathrm{T}\mathrm{A}}0$ |

Infrastructure | ${\left(\frac{\mathrm{k}\mathrm{g}\mathrm{i}\mathrm{n}\mathrm{f}\mathrm{r}\mathrm{a}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{u}\mathrm{c}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{e}\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{s}}{\mathrm{b}\mathrm{i}\mathrm{o}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{h}\mathrm{a}\mathrm{r}\mathrm{v}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{d}}\right)}_{\mathrm{M}\mathrm{o}\mathrm{n}\mathrm{o}\mathrm{c}.}-{\left(\frac{\mathrm{k}\mathrm{g}\mathrm{i}\mathrm{n}\mathrm{f}\mathrm{r}\mathrm{a}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{u}\mathrm{c}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{e}\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{s}}{\mathrm{b}\mathrm{i}\mathrm{o}\mathrm{m}\mathrm{a}\mathrm{s}\mathrm{s}\mathrm{h}\mathrm{a}\mathrm{r}\mathrm{v}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{d}}\right)}_{\mathrm{I}\mathrm{M}\mathrm{T}\mathrm{A}}0$ |

Pillar | Indicator | Result |
---|---|---|

Use of resources | Energy | 0.38% |

Nutrient management | N bioremediation | 7.71% |

P bioremediation | 12.08% | |

C bioremediation | 2.63% |

Pillar | Indicator | Result |
---|---|---|

Use of resources | Feed–FCR | 37% |

Feed–Linearity | 50% | |

Water | 99.68% | |

Infrastructure | 63.30% | |

Nutrient management | N bioremediation | 22.34% |

P bioremediation | 75.61% |

Pillar | Indicator | Result |
---|---|---|

Use of resources | Feed–FCR | 34.90% |

Feed–Linearity | 28.58% | |

Water | 50.00% | |

Energy | 34.30% | |

Nutrient management | N bioremediation | 18.17% |

P bioremediation | 6.01% |

Pillar | Indicator | Result |
---|---|---|

Use of resources | Feed–Linearity | 57.13% |

Water | 90.00% | |

Energy | 71.57% | |

Infrastructure | 66.67% | |

Nutrient management | N bioremediation | 80.00% |

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© 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Checa, D.; Macey, B.M.; Bolton, J.J.; Brink-Hull, M.; O’Donohoe, P.; Cardozo, A.; Poersch, L.H.; Sánchez, I.
Circularity Assessment in Aquaculture: The Case of Integrated Multi-Trophic Aquaculture (IMTA) Systems. *Fishes* **2024**, *9*, 165.
https://doi.org/10.3390/fishes9050165

**AMA Style**

Checa D, Macey BM, Bolton JJ, Brink-Hull M, O’Donohoe P, Cardozo A, Poersch LH, Sánchez I.
Circularity Assessment in Aquaculture: The Case of Integrated Multi-Trophic Aquaculture (IMTA) Systems. *Fishes*. 2024; 9(5):165.
https://doi.org/10.3390/fishes9050165

**Chicago/Turabian Style**

Checa, Daniel, Brett M. Macey, John J. Bolton, Marissa Brink-Hull, Pauline O’Donohoe, Alessandro Cardozo, Luis Henrique Poersch, and Inmaculada Sánchez.
2024. "Circularity Assessment in Aquaculture: The Case of Integrated Multi-Trophic Aquaculture (IMTA) Systems" *Fishes* 9, no. 5: 165.
https://doi.org/10.3390/fishes9050165