Search

The rapid and aggressive colonization of the invasive macroalgae Rugulopteryx okamurae on the southern coast of Spain has caused an unprecedented environmental, health and economic impact. At present, the scientific community has focused on the valorisation of R. okamurae waste, as tonnes of collected biomass from this species end up in landfills. In this sense, the aim of this study was to assess, for the first time, the viability of the R. okamurae digestate as biofertilizer to growth the Mediterranean forage species Avena strigosa (black oat). Two anaerobic digestates, derived from the anaerobic digestion of the thermally pre-treated (120 °C; 45 min) and the zeolite-assisted mechanically pre-treated invasive macroalgae, were used in this study. Both digestates were compared with a commercial inorganic nutritive solution. The effect of different fertilizers and water availability on forage height, aerial, root and seed biomass, as well as photosynthetic activity and macro- and micronutrient forage content were studied. The control treatment showed the lowest height at the end of the experiment (0.38 m) and the digestate from the thermally pre-treated macroalgae treatment had the highest one (0.59 m). Final fresh and dry aerial biomass was separately significantly dependent on both fertilizer type and water stress. Final root and seed biomass were not significantly different among the treatments studied. The lowest photosynthetic activity was obtained from the control treatment (3.61 µmol m⁻² s⁻¹), while the highest was reached by the digestate where R. okamurae was thermally pre-treated (4.96 µmol m⁻² s⁻¹). The results of this study show that both digestates tested can be used effectively as organic fertilizer in the cultivation of black oats, obtaining production efficiency values similar (digestate from mechanically pre-treated macroalgae) or higher (digestate from thermally pre-treated macroalgae) than inorganic fertilizer.

The brown marine alga Rugulopteryx okamurae (R. okamurae) has quickly spread through the Mediterranean coasts since it was firstly spotted in the area in 2015. This alien species has already colonized a great part of the Mediterranean western coasts and displaced the local biota, disrupting the natural and autochthonous marine ecosystem. Moreover, the related ‘green’ tides also provoke environmental problems ashore that need to be addressed. Comprehending the potential of this unwanted biomass could be of vital importance to lessen its ecological impact. In this study, the ashore R. okamurae was assessed for its potential as raw material for the extraction of reducing sugars and polyphenolic compounds with antioxidant capacities. The extraction process was evaluated and optimized using the response to surface methodology (RSM) combined with a modified Box-Behnken design. Initially, 2 key operational factors were identified as the most influential parameters (i.e. drying temperature and milling time). However, the type of solvent and the use of zeolite were included in the design as factors that potentially could have a significant impact on the process. The analyzed responses were the extraction yields for total phenolic compounds (TPC) and reducing sugars (RS). For the extraction of TPC the optimized methodology was based on the use of ethanol as solvent, a drying temperature of 60 °C and a zeolite-assisted milling time of 60 s, reaching a maximum yield of 15.33 ggallic acid kg−1. For the extraction of RS the optimized methodology was based on the use of water as solvent, a drying temperature of 100 °C and a zeolite-absence milling time of 50s, reaching a maximum yield of 10.42 gglucose kg−1.