South et al., 2022), particularly in suspended rope cultures (Lachance et al., 2008), where high densities and secondary settlement can cause detachment of smaller individuals (Lauzon-Guay et al., 2005 P. Adverse environmental conditions (e.g., strong storms Rasilla et al., 2018), especially offshore, can lead to substantial mussel losses (up to 54%, P. galloprovincialis in offshore systems is hampered by the current dependence on wild-collected juveniles (“spat”) on ropes or through harvesting from the shore (Azpeitia, Ortiz-Zarragoitia, et al., 2017 Fernández-Reiriz et al., 2016), making the production susceptible to annual fluctuations in spat supply because of unpredictable environmental conditions (Kamermans & Capelle, 2019 Skelton et al., 2021). Sustainable mussel farming is driving an increased interest in offshore aquaculture, which can support a faster and healthier growth of farmed species (Barillé et al., 2020 Kirchhoff et al., 2011), and is considered to reduce nutrient loadings into coastal environments (e.g., Bristow et al., 2008 Vezzulli et al., 2008). Spain is the largest producer of bivalves in Europe (287,000 t in 2018 Food and Agriculture Organization, 2020), with 94% of production devoted to cultures of the Mediterranean mussel Mytilus galloprovincialis (271,000 t year −1 Wijsman et al., 2019). Positive environmental impacts, good nutritional value, and significant health benefits have fuelled an expansion of bivalve aquaculture industry, which reached a yield of ~17 MT in 2018 (~35 billion USD Food and Agriculture Organization, 2020). Bivalves (clams, scallops, oysters, mussels) offer numerous benefits to human health, with a lower environmental footprint compared with other meats and many crop plants, providing a higher protein content than beef, and supplying a rich source of essential fatty acids and micronutrients (Willer & Aldridge, 2019a). ![]() To meet the drive toward greater sustainability, the marine aquaculture sector is expanding toward lower trophic level cultures such as macroalgae and bivalve mollusks (Bostock et al., 2010 Buck et al., 2017 Gentry et al., 2019 Willer & Aldridge, 2020b). By sourcing encapsulated algae from aquaculture side streams, microencapsulated feeds can further promote circular economies. galloprovincialis spat production can significantly reduce nursery costs compared with commercial feeds or cultured microalgae. Supplementing microencapsulated feeds with the commercial microalgal diet did not significantly improve growth performances (9.3 ± 2.3 μm day −1 ΔCI: 4.7 ± 1.4%) relative to mussels fed microcapsules alone. Spat fed microcapsules grew at comparable rates, and body condition rose at higher levels (shell growth rates: 8.5 ± 3.7 μm day −1 ΔCI: 6.1 ± 1.1%) relative to those fed commercial microalgae (8.5 ± 5.7 μm day −1 ΔCI: 3.3 ± 0.8%). Unsupplemented spat showed no growth and little change in body condition (CI). Spat (6.8 ± 1.1 mm) were supplied with different diets for 6 weeks: commercial microalgal diet (A), microencapsulated feeds containing a 1:1 blend of the macroalga Undaria pinnatifida and the microalga Schizochytrium (BioBullets BB), or commercial microalgae and BioBullets combined (ABB). The aim of this study was to assess the impact of dietary alternatives to commercial algal feeds (Shellfish Diet 1800) on the survival and growth of Mytilus galloprovincialis spat, widely farmed in Europe. Nursery culture of bivalves is, however, dependent on nutritious, cost-efficient, and more reliable diets for spat. Inland culture of mussel spat can play an important role in supporting extensive mussel farming. ![]() Global expansion of bivalve aquaculture can drive sustainable protein production.
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