Abstract
Mussel farming, compared to marine finfish aquaculture, represents an environmentally friendly alternative for a high quality protein source and can at the same time be a measure to remove excess nutrients in eutrophic areas. As such, it is considered as a promising ‘blue growth’ potential and promoted within the European Union. To expand mussel aquaculture, new regions have to be considered because there are multiple marine usages, and spatial limitations occur in coastal areas. The brackish Baltic Sea might be considered for expansion of mussel aquaculture. This study focusses on estimated production potential, economic profitability and nutrient remediation potential of mussel farming at different salinities. Four experimental mussel farms were set up along the German Baltic coast at salinities ranging from 7 to 17 psu. Collected growth data was used to calibrate and validate a Dynamic Energy Budget model and to predict the potential mussel production at twelve sites along the German coast. The estimated production and nutrient removal was used to assess economic profitability, assuming two usages of the harvest: human consumption and mussel meal production. Measured mussel specific growth rates increased with salinity from 0.05 mm d-1 in Greifswald Bay to 0.11 mm d-1 in Kiel Fjord. Within 6 months, a one-hectare farm could produce from 1 t (Darss-Zingst-Bodden-Chain) to 51 t (Flensburg) fresh mussels and remove 1.1 to 27.7 kg P and 24.7 to 612.7 kg N, respectively. Mussel farms at sites west of Rostock at salinities >10 psu could produce 5 cm mussels within 18 months, but only farms at Flensburg, Eckernförde and Kiel Fjord became profitable at a farm size of 4 ha (160,000 m³) at current market prices of 2.2 € kg-1. Regardless of the farm size, none of the farm sites could operate profitable if fresh mussels were sold for animal feeding at sales price of 0.06 € kg-1. Yearly nutrient removal costs at a small-scale farm (1 ha) ranged between 162 € (Flensburg) and 4,018 € (Darss-Zingst-Bodden-Chain) per kg nitrogen, and 3,580 € and 88,750 € per kg phosphorus, respectively.
Highlights
Mollusk aquaculture plays an important role across the globe
The present study evaluates the feasibility and profitability of implementing mussel aquaculture along the German Baltic Sea coast
Mussel farming represents an environmentally friendly alternative for a high quality protein source that at the same time can be a measure against eutrophication in the brackish Baltic Sea
Summary
Mollusk aquaculture plays an important role across the globe. Its production in Asia rose up to 16,000,000 t in 2017, while European production stagnated at 630,000 t. Monitoring sites closest to the mussel farms (Figure 1) were chosen to compare longterm environmental conditions (salinity, chl-a, and water temperature) between sites and to force the mussel growth model. Modeled data combined with former studies on mussel farm densities were used to estimate production capacity along the German Baltic Sea as well as generating an outlook of mussel farming in low saline waters. A mussel loss of 10% was applied throughout the growing period due to natural loss (self-thinning), handling (maintenance, grading, socking, and cleaning), and non-marketable sizes (for human consumption mussels) (Frechette et al, 2010; Cubillo et al, 2015; Haas et al, 2015; Nielsen et al, 2016; Taylor et al, 2019) This might change with salinity, but was not evaluated in former studies or this study. More details on the methodology to assess economic profitability can be found in the Supplementary Material (see section “Methodology to Assess Economic Profitability”)
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