Analysis of coastal and offshore aquaculture: application of the FARM model to multiple systems and shellfish species

The Farm Aquaculture Resource Management (FARM) model has been applied to several shellfish species and aquaculture types. The performance of the FARM model, developed to simulate potential harvest, key financial data, and water quality impacts at the farm-scale, was tested in five systems in the European Union: Loch Creran, Scotland (Pacific oyster), Pertuis Breton, France (blue mussel), Bay of Piran, Slovenia (Mediterranean mussel), Chioggia, Italy (Mediterranean mussel) and Ria Formosa, Portugal (Manila clam). These systems range from open coasts to estuaries, and are used for shellfish aquaculture by means of different cultivation techniques (e.g. oyster bottom culture in Loch Creran and mussel longlines and poles in Pertuis Breton). The drivers for the FARM model were supplied by measured data, outputs of system-scale models or a combination of both. The results (given in total fresh weight) generally show good agreement with reported annual production (shown in brackets) at each farm: simulated production of 134 tons of Pacific oyster in Loch Creran (150 tons, −10%), 2691 tons of blue mussel in Pertuis Breton (2304 tons, +17%), 314 tons of Mediterranean mussel in the Bay of Piran (200 tons, +57%), 545 tons of Mediterranean mussel in Chioggia (660 tons, −17%) and 119 tons of Manila clam in Ria Formosa (104 tons, +15%). The nitrogen mass balance for each farm was also determined with the FARM model. The net removal of nitrogen (N) by the farms was estimated to correspond to 1206 population equivalents per year (PEQ y−1) in Loch Creran, 93503 PEQ y−1 in Pertuis Breton, 9196 PEQ y−1 in the Bay of Piran, 97916 PEQ y−1 in Chioggia and 8613 PEQ y−1 in Ria Formosa. The aggregate income due to both the shellfish sale and substitution value of landbased fertilizer reduction or nutrient treatmentwas estimated to be about 700 k€ y−1 in Loch Creran, 30,706 k€ y−1 in Pertuis Breton, 3000 k€ y−1 in the Bay of Piran, 30,000 k€ y−1 in Chioggia, and 5000 k€ y−1in Ria Formosa. Outputs of FARM may be used to analyse the farm production potential and profit maximization according to seeding densities and/or spatial distribution. Results of a marginal analysis for all the study sites were determined. As an example, profit maximization in Loch Creranwas obtained with 97 tons of seed, resulting in a total production of 440 tons (profit of 2100 k€ for a culture period of about 2 years). FARM additionally integrates the well-known ASSETS model, for assessment of farm-related eutrophication impacts. The assessment results for the five study sites show that water quality is either maintained or improved in all farms under standard conditions of culture practice. FARM results may be used by farmers to analyse farm production potential and by managers for environmental assessment of farm-relatedwater quality impacts,whether positive or negative. It is a useful tool for all stakeholders for the valuation of nitrogen credits, which may be traded as part of an integrated catchment management plan. The FARM results were scaled up to determine a net value of 11–17 billion € y−1 of ecosystem goods and services, provided by shellfish culture towards reducing eutrophication in the coastal waters of the European Union. These numbers highlight the role that extractive organic aquaculture plays in integrated coastal zone and nutrient emissions management.