Panel 1
Paolo Tomassetti, Tommaso Petochi
The indicator provides an estimate of the input and removal of nitrogen and phosphorus, respectively produced by farmed fish and cultivated mussels, in the coastal marine environment where aquaculture activities take place.
The balance between nutrient inputs from farmed fish and nutrient removal by molluscs allows the estimation, at the regional scale, of the net quantitative contribution of aquaculture to trophic processes along the Italian coastline.
At the national level, compared with the 2021–2022 biennium, 2023 shows a reduction in nitrogen and phosphorus inputs, but also a decrease in the removal of these nutrients due to a decline in the production of both marine fish and farmed mussels.
At the regional level, in Veneto, Emilia-Romagna, Abruzzo, Molise and Marche, nitrogen and phosphorus removal by mussels exceeds nutrient inputs from fish farming, owing to the presence of numerous mussel farming facilities and the absence of intensive fish farming activities.
Intensive aquaculture of fish species in transitional waters and coastal marine areas results in the release of nitrogen- and phosphorus-based compounds.
Nutrient inputs to the environment occur through the discharge of wastes such as uneaten feed, metabolic excretion products and faeces. These wastes may be organic, in solid and/or dissolved form, or inorganic, and consist largely of carbon, nitrogen and phosphorus.
When the release of these compounds exceeds the environmental carrying capacity, i.e. the natural assimilative capacity of the receiving ecosystem, alterations may occur, particularly in the water column and sediments.
Such effects are usually localized and limited in magnitude; however, under certain environmental and farming conditions, eutrophication processes, reductions in dissolved oxygen and local-scale biodiversity alterations may develop.
Nitrogen and phosphorus removal is carried out by extensive farming of bivalve molluscs, which use nutrients present in the water column as a trophic resource, thereby reducing their concentrations.
The indicator provides an estimate of nitrogen and phosphorus inputs or removal, respectively attributable to fish and mussels, in the coastal environment where aquaculture activities are carried out.
The indicator is useful for carrying capacity assessments within processes aimed at identifying Allocated Zones for Aquaculture (AZA).
To provide an estimate of the contribution of marine aquaculture to organic enrichment in coastal waters.
The balance between nutrient inputs from farmed fish and nutrient removal by bivalve molluscs allows estimation of the net quantitative contribution of aquaculture to trophic processes along the Italian coastline.
At the European level, legislation does not define common objectives and leaves Member States responsible for establishing rules aimed at limiting the environmental impact of aquaculture activities.
In Italy, Legislative Decree No. 152/2006 on environmental regulations specifies the requirements for waters designated for mollusc farming (Article 87) and establishes nitrogen and phosphorus limits (Article 101, discharge regulations) where effluents from fish farming facilities with stocking densities greater than 1 kg/m² or water flow rates equal to or lower than 50 L/s are discharged into sensitive areas (Tables 1 and 2 of Annex 5, Part III).
With regard to aquaculture facilities in freshwater, transitional or marine environments, Article 111 of Legislative Decree 152/2006 provides for a specific Ministerial Decree under the responsibility of the Ministry for the Environment and Energy Security (MASE). This decree, developed in coordination with the Ministries responsible for agriculture, infrastructure and transport, and productive activities, and following agreement with the State–Regions Conference, is intended to define criteria for limiting the environmental impacts of aquaculture activities.
A draft Ministerial Decree has been prepared by an interministerial working group established by MASE; however, to date it has not yet been adopted, and no specific environmental legislation is available for the monitoring and control of aquaculture-related environmental impacts.
Legislative Decree No. 190 of 13 October 2010, implementing the Marine Strategy Framework Directive (2008/56/EC), identifies nitrogen and phosphorus inputs from aquaculture as pressure and impact elements and therefore requires their quantitative assessment.
Accordingly, during the implementation of the directive, monitoring activities carried out by ISPRA–SNPA are foreseen to assess organic enrichment generated by aquaculture facilities (Descriptor 5 “Eutrophication”; Operational Plan of Activities 2021–2022–2023, Ministerial Decree of 2 February 2021).
However, since monitoring is conducted on a semi-annual basis and, in some cases, in farming areas also exposed to other sources of organic enrichment (e.g. ports, river mouths), it does not allow the identification of a clear causal relationship between fish farming activities and measured nitrogen and phosphorus concentrations at sampling stations.
Therefore, the data produced by this indicator are also used for reporting purposes for the three subregions (Adriatic, Ionian, Western Mediterranean) under Descriptor 5 of the Marine Strategy.
In addition, in 2024 Regulation (EU) 2024/1244 entered into force, concerning the reporting of environmental data from industrial installations and the establishment of an industrial emissions portal. The Regulation, applicable from 1 January 2028, also requires annual reporting of pollutant emissions, including nitrogen and phosphorus, for “feed-based aquaculture” facilities with an annual production capacity exceeding 500 tonnes (Annex I; Annex II).
Panel 2
COM (2019) 640 final. The European Green Deal.
COM (2020) 381 final. A “From producer to consumer” strategy for a fair, healthy and environmentally friendly food system.
COM (2021) 236 final. Strategic orientations for a more sustainable and competitive EU aquaculture for 2021 – 2030
COM (2025) 281 final. The European Ocean Pact.
Resolution 31 July 2023. Presidency of the Council of Ministers. Interministerial Committee for Maritime Policies. Approval of the Sea Plan for the three-year period 2023-2025.
FAO. 2024. The State of World Fisheries and Aquaculture. 2024. Blue transformation in action. Rome.
Islam, M. S., 2005, Nitrogen and phosphorus budget in coastal and marine cage aquaculture and impacts of effluent loading on ecosystem: review and analysis towards model development. Marine Pollution Bulletin 50, 48-61.
ISPRA, various years, Environmental data yearbook
Lupatsch, I., Kissil, G. W., 1998, Predicting aquaculture waste from gilthead seabream (Sparus aurata) culture using a nutritional approach. Aquatic Living Resources 11: 265-268.
Marino G., Petochi T., Cardia F. (2020). "Assignment of Marine Zones for Aquaculture (AZA). Technical Guide", 214 p., ISPRA Technical Documents 2020. https://www. isprambiente. gov. it/it/pubblicazioni/documenti-tecnici/associazione-di-zone-marine-perlacquacoltura-aza-guida-tecnica
MIPAAF (2021). National Strategic Plan for Aquaculture Italy 2021-2027. Pp. 164.
Palmerini R., Bianchi C. N., 1994, Biomass measurements and weight-to-weight conversion factors: a comparison of methods applied to the mussel Mytilus galloprovincialis . Mar. Biol., 120: 273-277.
Porrello S., Brigolin D., Marino G., Pastres R., Scardi M., 2013A, Nitrogen and phosphorus load from aquaculture activities. Methodological note as Supporting Documents for the Italian implementation of Directive 2008/56CE.
Porrello S., Brigolin D., Tomassetti P., Scardi M., Pastres R., 2013B, Estimation of nitrogen and phosphorus fluxes from Mariculture: application of models to a case study (Adriatic Sea). Biol. Mar. Medit., 20(1): 110-111.
EMFF Operational Program 2021-2027. https://www. politicheagricole. it/flex/cm/pages/ServeBLOB. php/L/IT/IDPagina/8752
Regional Plan on Aquaculture Management in the Framework of Article 15 of the Land Based Sources and Activities Protocol (Decision IG.26/7 – 2023)
Smaal A. C., Vonck A. P. M. A., 1997, Seasonal variation in C, N and P budgets and tissue composition of the mussel Mytilus edulis. Mar. Ecol. Prog. Ser., 153: 167-179.
Environmental assessment pursuant to Art. 8 of the Legislative Decree. 190/2010. MSFD Summary Report. D5- Eutrophication. October 10, 2024
The estimates provided by the indicator refer to the three main species farmed in Italian coastal marine areas: gilthead seabream (Sparus aurata), European seabass (Dicentrarchus labrax) and Mediterranean mussel (Mytilus galloprovincialis).
The two fish species account for 93% of national marine finfish production, while mussels contribute 72% of mollusc aquaculture production in coastal marine waters.
At present, reliable models for estimating nitrogen and phosphorus release or removal by other farmed species (e.g. oysters and clams) are not available; however, these species are less relevant in terms of production volumes.
From a regulatory perspective, no legally established reference values exist for nitrogen and phosphorus inputs from aquaculture. Such values should be developed based on multiple criteria, including species, farming system, production volumes, environmental characteristics of farming sites and area-specific carrying capacity, also with a view to identifying Allowable Zones of Effect (AZE) on a site-specific basis.
In 2023, the Regional Plan on Aquaculture Management for the Mediterranean was finalized within the UNEP/MAP framework. The plan identifies guiding elements for controlling and reducing pollution caused by marine aquaculture facilities and предусматри site-specific environmental monitoring programmes.
Among the parameters considered, in addition to nitrogen and phosphorus released into the water column and sediments, biological indices of benthic fauna are included, as their alteration may indicate chronic effects resulting from nutrient accumulation in sediments derived from aquaculture sources.
Specific monitoring protocols for assessing nutrient impacts from aquaculture activities in the water column and sediments are currently being developed by the SNPA Thematic Network RR-TEM 26-2 on Sustainable Aquaculture.
Marine Strategy monitoring programmes will also need to include more targeted environmental surveys to assess the contribution of aquaculture to “Eutrophication” (Descriptor 5). Previous Marine Strategy monitoring programmes and protocols did not allow for a comprehensive assessment of nutrient enrichment from aquaculture sources in coastal marine environments.
Data quality assessment
MASAF (Ministry of Agriculture, Food Sovereignty and Forestry)
CREA (Council for Research and Experimentation in Agriculture)
EUROSTAT (Statistical Office of the European Communities)
The production data are those recorded by MASAF pursuant to Regulation (EC) no. 762/2008 for the years 2021, 2022 and 2023 and published in aggregate form by Eurostat https://ec. europa. eu/eurostat/data/database .
Coastal regions
2021, 2022, 2023
Indicator assessment
Mathematical models based on the physiology of farmed organisms were used to estimate nitrogen and phosphorus inputs and removal, specifically the proportion of nutrients supplied as feed or present in the water column that are either incorporated into biomass or released into the environment.
Such models are currently available for the two most important marine fish species in Italy in terms of production volume, namely gilthead seabream and European seabass. For these species, estimates of organic and inorganic compound releases were obtained using the models proposed by Lupatsch et al. (1998) and Islam (2005).
These models consist of equations relating nitrogen and phosphorus release per tonne of fresh weight produced to the average feed conversion ratio (FCR), defined as the ratio between feed supplied and biomass gain, through simple linear regressions based on previous studies.
Given the central role of FCR, species-specific values were adopted, including an average value as well as minimum and maximum estimated values for each species. This approach allowed the construction of an independent confidence interval for the regression line and thus an estimation range for each FCR value.
For nutrient removal by farmed molluscs, estimates refer exclusively to mussels (Mytilus edulis), using relationships described by Palmerini and Bianchi (1994) and Smaal and Vonck (1997). These estimates consist of equations that calculate the average nitrogen and phosphorus content per unit of farmed biomass.
Required parameters include conversion from wet weight (WW) to ash-free dry weight (AFDW), subsequent conversion from AFDW to dry flesh weight (DFW), and finally conversion from DFW to nitrogen and phosphorus quantities. Model description and application are reported in Porrello et al. (2013A–B).
The indicator is developed at the regional scale, but the methodology can also be applied locally and in all coastal marine areas where fish and mollusc farming coexist.
Nitrogen and phosphorus inputs from fish farming are considered as total inputs from euryhaline fish, obtained by summing seabream and seabass estimates, without distinguishing farming systems (land-based tanks or offshore cages).
The analyses refer to the 14 Italian coastal regions hosting marine aquaculture facilities.
In 2023, estimated nitrogen and phosphorus inputs from fish farming amounted to 1,186.1 and 204.15 tonnes per year, respectively, while nitrogen and phosphorus removal by farmed mussels amounted to 365.1 and 25.15 tonnes per year.
The resulting net balance was therefore 820.8 tonnes of nitrogen and 179 tonnes of phosphorus per year, with mussels removing approximately 31% of nitrogen and 12% of phosphorus.
In 2021, national estimates showed nitrogen and phosphorus inputs from fish farming of 1,279.1 and 220.1 tonnes per year, respectively, while removal by farmed mussels amounted to 395.5 tonnes of nitrogen and 27.2 tonnes of phosphorus per year.
The resulting annual net balance was 883.6 tonnes of nitrogen and 192.9 tonnes of phosphorus, with mussels removing approximately 31% of nitrogen and 12% of phosphorus.
In 2022, inputs increased to 1,333.7 tonnes of nitrogen and 229.3 tonnes of phosphorus per year, while mussel removal decreased to 385.8 tonnes of nitrogen and 26.6 tonnes of phosphorus per year.
The net balance therefore increased to 947.9 tonnes of nitrogen and 202.8 tonnes of phosphorus per year, with mussels removing 29% of nitrogen and 11% of phosphorus.
Compared to 2021, 2022 recorded an increase in nutrient inputs from fish farming of approximately 54.6 tonnes of nitrogen and 9.2 tonnes of phosphorus, while nutrient removal by mussels declined by 9.7 tonnes of nitrogen and 0.7 tonnes of phosphorus.
This pattern reflects a slight increase in seabass and seabream production alongside a reduction in mussel production.
Data for 2023 indicate a decrease relative to 2022 in nitrogen and phosphorus inputs from fish farming, by approximately 147.6 and 25.2 tonnes respectively. Mussel-driven nutrient removal further declined in 2023, by 20.5 tonnes of nitrogen and 1.4 tonnes of phosphorus.
This trend is attributable to a contraction in both fish and mussel production observed in 2023 compared to the previous biennium.
Overall, the national net nutrient balance from marine aquaculture increased in 2022 by approximately 64.3 tonnes of nitrogen and 9.9 tonnes of phosphorus compared to 2021, but decreased in 2023 by 127 tonnes of nitrogen and 23.8 tonnes of phosphorus compared to 2022.
The importance of developing and promoting sustainable aquaculture systems capable of providing ecosystem services, such as bivalve mollusc farming, is emphasized.
Data
Table 1: Nitrogen and phosphorus quantities from aquaculture facilities in the marine environment (2021–2023)
ISPRA processing based on MASAF–CREA and EUROSTAT data
Figure 1: Nitrogen balance from aquaculture facilities in the marine environment (2023)
ISPRA processing based on MASAF–CREA and EUROSTAT data
Figure 2: Phosphorus balance from aquaculture facilities in the marine environment (2023)
ISPRA processing based on MASAF–CREA and EUROSTAT data
Table 1 reports nitrogen and phosphorus inputs from seabass and seabream farming and nutrient removal by mussels for the years 2021, 2022 and 2023.
Fish farming data were calculated by aggregating both offshore cage farming and land-based coastal systems, and for both seabass and seabream.
Mussel data refer to the most widespread farming practice in Italy, namely suspended longline systems in the water column.
Tuscany, where no mussel farms were present until 2023, shows the highest nitrogen and phosphorus inputs from aquaculture facilities, while Emilia-Romagna exhibits the highest nutrient removal in coastal waters. This reflects mussel production volumes, which in Emilia-Romagna account for 25% of national aquaculture production.
After Tuscany, the lowest nutrient removal was recorded in Calabria, where only two mussel farms were operating in 2023.
In Marche, Abruzzo, Molise and Basilicata, no fish farming facilities are present.
For all three years, in Veneto and Emilia-Romagna, nitrogen and phosphorus removal exceeded inputs because mussel production volumes and the number of facilities are higher and no intensive fish farming is present.
In Tuscany, Lazio, Sardinia, Friuli-Venezia Giulia, Apulia, Liguria and Campania, the overall net balance indicates higher nitrogen and phosphorus inputs due to greater farmed fish production.