Production Characteristics and Optimization of Mitigation Mussel Culture

Abstract

Bivalve environmental services have become a focal point for their inherent role in the management of eutrophication, while active cultivation has become increasingly acknowledged as a mechanism for integrated nutrient reduction. In recent years, cultivation practices designed specifically for nutrient extraction have emerged; "mitigation culture." While modeling efforts have been able to describe expanded potential of these services, only a single commercial pilot scale, realworld demonstration, has been documented. Over two production seasons (2017-2018), the optimization of nutrient extractive potential of mussels (Mytilus edulis) at full commercial-scale was evaluated by first testing multiple density configurations of conventional longline-spat collector setups and potential harvest times, then by comparing different cultivation technologies at three farms. Potential biomass volumes of 770-1700 t with longlines and 2100-2600 t on nets was demonstrated in fullscale production (18.8 ha), yielding 0.6-1.27 t N ha −1 and 0.04-0.1 t P ha −1 , and 1.63-2.0 t N ha −1 and 0.1-0.12 t P ha −1 respectively. In general, 1 t of harvested mitigation mussels will yield 13.7 kg N and 0.9 kg P. Winter harvests exhibited higher yields (103-124%) than early spring harvests on optimized configurations, favoring an abbreviated production season. Production potential was similar between sites, despite differing environmental conditions, indicating eutrophic waters are suitable for expanded mitigation production. This study presents for the first-time production data of mitigation mussels utilizing different configurations and technologies to maximize yield and nutrient extraction potential.

Site selection of mussel mitigation cultures in relation to efficient nutrient compensation of fish farming

“…The uncertainty test with different X k values showed that the modeled mean values of mussel harvest and nutrient removal potentially could vary by −20 to +31% within a mussel farm. This estimate is comparable to field data, where the standard deviation for mussel farm N removal was ±20−33% of the mean value between all sites and seasons (Taylor et al 2019). The farm biomass was estimated from the individual mussel biomass multiplied by the population density per m 3 of the farm based on a previous study in the Limfjorden (Nielsen et al 2016).…”

“…The initial shell length was 0.62 cm, and 1 cohort of mussels was followed over time (Nielsen et al 2016). Harvest was assumed to take place on 1 December to avoid damage from ice cover and storms during winter (Taylor et al 2019). A dynamic energy budget (DEB) model was used to describe the growth of individual mussels within the cohort in response to temperature, salinity and food concentrations (Maar et al 2015).…”

“…The farm biomass was estimated from the individual mussel biomass multiplied by the population density per m 3 of the farm based on a previous study in the Limfjorden (Nielsen et al 2016). A more recent study in the Limfjorden showed that mussel abundance in the farm could be increased by a factor of 2 in order to achieve a higher harvest (Taylor et al 2019). Hence, the nutrient removal estimated by the farms in the present study is a conservative estimate, as the density of mussels potentially could be increased by increasing the number of loops, extending the loops further with depth or using another farm system, e.g.…”

Nitrogen and Phosphorous Content in Blue Mussels (Mytilus spp.) Across the Baltic Sea

“…Low spring nitrogen contents in cultivated blue mussels are consistent with primary gamete release (Pieters et al, 1980;Okumus and Stirling, 1998;Fernández et al, 2015). Taylor et al (2019) recommended late autumn through winter harvests in order to maximize nutrient extraction efficiency. This will additionally avoid potential loss of nutrient content overlapping with gamete release, and permit new spat collection in the late spring/early summer.…”

“…The persistence and magnitude of eutrophication in the Baltic Sea requires cost-effective measures to reduce nutrients and to achieve a good ecological status (GES) based on the Water Framework Directive (WFD, European Parliament, 2000) and the Marine Strategy Framework Directive (MSFD, European Parliament, 2008). Extensive mussel aquaculture on longlines or tube-net systems (e.g., Smart Farm) is highly discussed as such a measure in the greater Baltic Sea (Lindahl and Kollberg, 2008;Stadmark and Conley, 2011;Petersen et al, 2012Petersen et al, , 2014Petersen et al, , 2019Nielsen et al, 2016;Hedberg et al, 2018;Gren, 2019;Taylor et al, 2019;Kotta et al, 2020). The amount of nutrients that can hereby be removed depends on several parameters, such as nutrient content of the mussels, growth rates, harvesting time, and farm set up (Capillo et al, 2018;Taylor et al, 2019).…”