Valorisation of invasive North Sea macroalgae as functional feed additives to improve disease resilience in Pacific white shrimp (Litopenaeus vannamei)

Ulva australisSargassum muticumSeaweed phytochemicalsAquaculture nutritionLitopenaeus vannameiAHPNDGut microbiomeGrowth performanceInvasive macroalgae such as Ulva australis and Sargassum muticum are increasingly abundant along European coastlines and represent a potentially valuable source of bioactive compounds for sustainable aquaculture. This study evaluated the potential of invasive North Sea macroalgae as functional feed additives to enhance disease resilience in Pacific white shrimp (Litopenaeus vannamei) challenged with Vibrio parahaemolyticus. Extracts from two U. australis populations (The Netherlands and France) and one S. muticum population were prepared using 70% ethanol and characterized through proximate composition analysis, total phenolic content (TPC), and HPLC. Antibacterial activity against V. parahaemolyticus was assessed using minimum inhibitory concentration (MIC) assays. Shrimp post-larvae (PL10; 42 ± 0.6 mg) were fed diets containing 1% or 3% seaweed extract for 28 days, after which growth performance, survival, resistance to V. parahaemolyticus, and gut microbiome composition were evaluated.Gallic acid and quercetin were detected in all seaweed extracts. Total phenolic content was highest in U. australis from the Netherlands (269 ± 7.86 µg GAE g⁻¹), followed by S. muticum (89 ± 8.65 µg GAE g⁻¹) and U. australis from France (69 ± 6.50 µg GAE g⁻¹). Antibacterial activity was likewise observed for all seaweed extracts, with MIC values of 12.5 mg mL⁻¹ for U. australis and 25 mg mL⁻¹ for S. muticum. Shrimp fed seaweed-supplemented diets exhibited significantly higher survival rates following the V. parahaemolyticus challenge compared to the control group (p < 0.05). The strongest protective effect was observed in the 3% U. australis (The Netherlands) treatment group, where survival increased from 60.00 ± 12.02% in the control to 74.44 ± 8.39% in the seaweed-supplemented group. In contrast, weight gain, specific growth rate, and feed conversion ratio were generally superior in the control group. Gut microbiome composition showed treatment-related shifts in bacterial abundance, although overall microbial diversity remained unchanged.These results indicate that invasive North Sea macroalgae can be valorised as functional aquafeed ingredients that enhance resistance against V. parahaemolyticus infection in L. vannamei. Although growth benefits were not observed, the improved post-challenge survival highlights the potential of these seaweed extracts as functional feed additives contributing to more resilient and sustainable shrimp aquaculture.