A Sustainable Approach to Managing Invasive Macroalgae: Assessment of the Nutritional Profile and the Potential for Enteric Methane Mitigation of Rugulopteryx okamurae

The expansion of the invasive Asian macroalgae Rugulopteryx okamurae along the coasts of the Azores represents a significant challenge for local marine biodiversity. A promising approach to managing the biomass produced by this alien alga is to valorize it in the context of the blue economy. This study characterizes and evaluates the potential of R. okamurae biomass for incorporation into cattle feed, with a focus on mitigating enteric methane production. The nutritional value of R. okamurae, its digestibility, and its potential as a mitigating agent for enteric methane production were analyzed in vitro. The results indicate that the inclusion of 5% R. okamurae in the diet significantly (p < 0.05) reduced accumulated methane production by 98% after 24 h of incubation. The addition of 1% algae over the same period resulted in a 38% reduction in methane production. However, a significant decrease (p < 0.05) in gas production of 57.02% and 73.5% was also observed in relation to control, with the inclusion of 1% and 5%, respectively, during 96 h. Nutritionally, R. okamurae was found to have a crude protein content of 18.68% and fiber (NDF) of 55.71% of DM. It is also worth highlighting the high content of ash (31.86%) that was identified in these brown macroalgae. In conclusion, the fresh biomass of R. okamurae could serve as a functional ingredient in cattle feed to mitigate enteric methane production, provided it is used in low percentages. However, it is important to emphasize that high concentrations in the first 12 h did not produce methane, which is also not recommended for enteric fermentation. However, before including it in animal feed, in vivo tests are needed to assess its toxicity.