Introduction
T he links between human footprint and ecosystem is becoming clearer , leading to the development of management tools that incorporate both scientific and socioeconomic information into decision making processes . The valuation of ecosystem services provided by human activities such as aquaculture becomes more prominently present in legislative context and may have the power to change public’s , often negative perception of aquaculture . Nevertheless, there is still a significant knowledge gap in systematically quantifying these ecosystem services . Dynamic Energy Budget (DEB) models offer the possibility to quantify nutrient emissions or eutrophication mitigation (N and P) of aquaculture production in dynamic environments, and coupled to spatial biogeochemical datasets, DEB models can provide information regarding spatial variability of these ecosystem services.
Bivalves removing suspended solids from the water that are excreted by finfish, is a classical example of IMTA (reference !) where nutrients are recycled to the benefit of the water quality. Quantification of the nutrient fluxes in IMTA setups remains a challenge. Thanks to a DEB extension that allows for quantification of product formation, such as shells, it is now also possible to quantify carbon cycles through farms.
Methods
Dynamic Energy Budget models provide a generic framework to estimate mass and energy balances. They can be applied to all living organisms and all ecological scales from cells to ecosystems. Applying DEB models to aquaculture relevant species enables quantification of several relevant variables including growth, reproduction, and physiological processes such as feeding, ingestion, assimilation, respiration and (pseudo-)faeces production.
N utrient fluxes through finfish and mussel farms in the whole Baltic Sea region were quantified using a DEB modelling framework (Kotta et al. 2023). DEB models for the rainbow trout and the Baltic mussel were parameterised and validated using in situ observation of the metabolic performance (e.g., respiration, growth, and reproduction) over a salinity gradient. Standardised fish and mussel farms where introduced and spatial distribution of nutrient uptake and nutrient emissions of these farms were evaluated.
Results
Finfish farms (standardized to 265 tons of wet weight production) on average emit 6500 kg N and 520 kg P to the water column during a production cycle. Mussel farms (standardized to 24 tons of wet weight production) remove on average 210 kg N and 25 kg P from the water column. Spatial variability of nutrient emission and incorporation of both finfish and mussel farms (Figure 1) is large in the Baltic. Nevertheless, simulations demonstrated that despite suboptimal mussel growth conditions, mussel farming has the potential to fully compensate for the discharge of nutrients from finfish farms and may thus represent a solution to sustainable finfish farming in the Baltic Sea region. Besides eutrophication mitigation, simulating filtration, incorporation and biocalcification enabled complete estimation of carbon budgets of shellfish farms.
Conclusion
DEB is a generic framework that enables quantification of ecosystem services related to nutrient and carbon fluxes in dynamic environment such as the Baltic Sea . It has the power to become an important tool in nutrient or carbon budgeting for single activities and can be used to quantify nutrient fluxes through IMTA setups.
References
Kotta, J., Stechele, B., Barboza, F. R., Kaasik, A., & Lavaud, R. (2023). Towards environmentally friendly finfish farming: A potential for mussel farms to compensate fish farm effluents. Journal of Applied Ecology.