Assessing the mechanical properties of biobased versus fossil-based ropes and their impact on the productivity and quality of mussel (<i> Mytilus</i> galloprovincialis ) in longline aquaculture: Toward decarbonization

Abstract

The expansion of offshore mussel aquaculture is intertwined with the rising demand for mussel grow -out ropes. Currently, these ropes are manufactured using fossil -fuel based or fossil -based plastics. In response to concerns about plastic pollution and sustainable aquaculture practices, biobased materials have emerged as more sustainable alternatives. Yet, the importance of the choice of raw materials, as well as the methods used in their production and sourcing, is key in determining the performance of materials in sea conditions within the context of aquaculture. This study evaluated the functionality of biobased ropes in terms of productivity and durability, comparing them to fossil -based counterparts during a one-year mussel culture in offshore conditions. Across oneyear culture, noteworthy mussel losses were observed in the fossil -based (65\%) ropes compared to the biobased B1 (53\%) and B2 (18\%) prototype ropes, B2 and B1 ropes yielding 85\% and 23\% more mussel (kg/ m rope) than the fossil -based ropes. Moreover, the higher correlations of shell length and body weight over time suggesting that biobased ropes may be more suitable substrates for mussel growth compared to fossil -based ropes. The structural distinction between the round and more uniform fine multifilaments in biobased ropes, as opposed to the clustered structure of flat fibres in fossil -based ropes, may have contributed to a more effective surface area for the initial attachment and growth of seeded mussels, avoiding subsequent losses. The use of biobased ropes contributed positively to the interplay between substrate structure, biofouling, and mussel attachment, which may be used for guiding further designs of aquaculture biobased gears. Despite seasonal variations, the final condition, proximate and fatty acid composition of mussel indicated their marketability and high nutritional quality. Higher shell length and mussel yields observed, indicating a potential for mussels cultivated on biobased ropes, especially in B2, to reach a higher market value. Regarding durability, linear density of biobased ropes remained unaltered after one-year offshore mussel culture. The biobased B2 rope prototype showed the highest ratio between the retention of mechanical properties (Load at Break and elongation) and the total mussel weight held for one year. The findings of this study validate the biobased B2 prototype as the most promising alternative to fossil -based ropes. It significantly boosted production yields of high -quality mussels while maintaining rope durability throughout one year in offshore culture. These results hold promise for reducing the reliance on fossilbased plastic ropes in mussel aquaculture, thereby contributing to decarbonization efforts.